|
OK...not the thermostat, now what? HELP!
Recap: Recently, boat started overheating for approx. 2 to 4 minutes
after startup. Temp goes to 220+F then it suddenly drops back to 150F and stays there, then all is fine until I get to my destination. The obvious culprit (I thought) was a faulty, sticky thermostat. I figured the thermostat simply does not open when it is supposed to (at approx. 160F) but eventually it does and the water cooling happens. Bought a new thermostat and replaced: no luck. Removed the thermostat entirely, closed the housing and started the boat: needle creeped up to 200+! Went home and tested both (old and new) thermostat in hot water: both appear to open at around 160F. So, it appears the problem is NOT the thermostat. I also disconnected the hose from the transom to the thermostat housing (the one drawing the water from the ocean). Started the boat for a few seconds and got a good flow so apparently no clogged intake either. I am assuming that water was pushed through by the impeller so that would mean the impeller is also doing its job (although I have actually not looked in there and impeller was replaced 2 months ago).. Now what? I am not sure what else to check. The alternator belt seems tight so I am also assuming the water pump is running at the correct speed (but I don't really know). In the manual, they list the typical symptoms of overheating (loose belt, clogged intakes, bad hoses, defective thermostat, worn or damaged stern drive water pump). Pretty much the stuff discussed above but also a couple that I have no clue what they are talking about: a) Excessively advanced or retarded ignition timing (????) b) Leakage of air or exhaust into the suction side of the stern water pump (????) I am not very mechanically inclined so I get lost quickly in the jargon. Anyone can offer suggestions, advices, comments, recommendations? I am getting desperate! Problem is I have a cabin that is boat-access only so no boat = stay home instead of enjoying a gorgeous weekend at the cabin... :( Andre |
Melandre wrote: Recap: Recently, boat started overheating for approx. 2 to 4 minutes after startup. Temp goes to 220+F then it suddenly drops back to 150F and stays there, then all is fine until I get to my destination. The obvious culprit (I thought) was a faulty, sticky thermostat. I figured the thermostat simply does not open when it is supposed to (at approx. 160F) but eventually it does and the water cooling happens. Bought a new thermostat and replaced: no luck. Removed the thermostat entirely, closed the housing and started the boat: needle creeped up to 200+! Went home and tested both (old and new) thermostat in hot water: both appear to open at around 160F. So, it appears the problem is NOT the thermostat. I also disconnected the hose from the transom to the thermostat housing (the one drawing the water from the ocean). Started the boat for a few seconds and got a good flow so apparently no clogged intake either. I am assuming that water was pushed through by the impeller so that would mean the impeller is also doing its job (although I have actually not looked in there and impeller was replaced 2 months ago).. Now what? I am not sure what else to check. The alternator belt seems tight so I am also assuming the water pump is running at the correct speed (but I don't really know). In the manual, they list the typical symptoms of overheating (loose belt, clogged intakes, bad hoses, defective thermostat, worn or damaged stern drive water pump). Pretty much the stuff discussed above but also a couple that I have no clue what they are talking about: a) Excessively advanced or retarded ignition timing (????) b) Leakage of air or exhaust into the suction side of the stern water pump (????) I am not very mechanically inclined so I get lost quickly in the jargon. Anyone can offer suggestions, advices, comments, recommendations? I am getting desperate! Problem is I have a cabin that is boat-access only so no boat = stay home instead of enjoying a gorgeous weekend at the cabin... :( Andre Aha. Depending on the accuracy of your description...... How fast does the temp climb to 220-250. Within 2 minutes or so after startup? How "suddenly" does it drop from 220 to 150? Your coolant will only cool so fast, so if it seems unnaturally quick it could be as simple as the sending unit. Since the thermostats passed the candy thermometer test, you know you have one good one and one spare. Sending unit is probably less expensive than a lot of other things you could fiddle around replacing, and if the temperature is changing by radical amounts in very short periods of time it is a reasonable suspect. |
The sender is a sensor which screws into the engine water jacket and changes
resistance as engine heats up or cools down. Since you gauge changes very fast, maybe the sender, gauge, or wiring problem is present. At this point, it may be a good idea to have a professional marine shop check your problem out. Just let them know what was all done so far which should reduce the costs.. "Melandre" wrote in message ... It takes a couple of minutes to get passed "normal temperature". Then another minute or so to climb over 200F. Then stays hot for 1 to 3 minutes (in a few occasions a bit longer than 3 minutes), then it drops back from well over 200F to 150F in about 3 - 5 seconds. I am not sure what you mean by "sending unit" but if you suggests that perhaps only the readout on the dashboard is screwed up, I doubt it because, for these few freaky minutes, I can really tell the engine is overheating (burning oil smell, block starts smoking a bit). Or maybe you are referring to yet another part that I am not aware of... It is also a simple raw water cooling system (not a closed one with coolant). Andre On 19 Aug 2005 22:15:49 -0700, wrote: Melandre wrote: Recap: Recently, boat started overheating for approx. 2 to 4 minutes after startup. Temp goes to 220+F then it suddenly drops back to 150F and stays there, then all is fine until I get to my destination. The obvious culprit (I thought) was a faulty, sticky thermostat. I figured the thermostat simply does not open when it is supposed to (at approx. 160F) but eventually it does and the water cooling happens. Bought a new thermostat and replaced: no luck. Removed the thermostat entirely, closed the housing and started the boat: needle creeped up to 200+! Went home and tested both (old and new) thermostat in hot water: both appear to open at around 160F. So, it appears the problem is NOT the thermostat. I also disconnected the hose from the transom to the thermostat housing (the one drawing the water from the ocean). Started the boat for a few seconds and got a good flow so apparently no clogged intake either. I am assuming that water was pushed through by the impeller so that would mean the impeller is also doing its job (although I have actually not looked in there and impeller was replaced 2 months ago).. Now what? I am not sure what else to check. The alternator belt seems tight so I am also assuming the water pump is running at the correct speed (but I don't really know). In the manual, they list the typical symptoms of overheating (loose belt, clogged intakes, bad hoses, defective thermostat, worn or damaged stern drive water pump). Pretty much the stuff discussed above but also a couple that I have no clue what they are talking about: a) Excessively advanced or retarded ignition timing (????) b) Leakage of air or exhaust into the suction side of the stern water pump (????) I am not very mechanically inclined so I get lost quickly in the jargon. Anyone can offer suggestions, advices, comments, recommendations? I am getting desperate! Problem is I have a cabin that is boat-access only so no boat = stay home instead of enjoying a gorgeous weekend at the cabin... :( Andre Aha. Depending on the accuracy of your description...... How fast does the temp climb to 220-250. Within 2 minutes or so after startup? How "suddenly" does it drop from 220 to 150? Your coolant will only cool so fast, so if it seems unnaturally quick it could be as simple as the sending unit. Since the thermostats passed the candy thermometer test, you know you have one good one and one spare. Sending unit is probably less expensive than a lot of other things you could fiddle around replacing, and if the temperature is changing by radical amounts in very short periods of time it is a reasonable suspect. |
A possibility ... until the thermostat opens, cooling water from the
impeller has to go somewhere as well as cool the manifolds etc. My understanding, a spring loaded t-valve accomplishes this (V6, V8). When I first disconnected the lines for winter storage, I came across this mechanism and wondered what it was. Perhaps this mechanism is at fault (stuck open a bit ... I dunno) ... and since you're in salt water you might consider a 140 (ok, 143) degree thermostat ... my understanding at 160+ the salt will separate from the water. Go to the bottom of this page to see the t-valve (nylon I guess balls spring loaded) which easily accessible by removing the water lines http://www.perfprotech.com/home/tech...oling-tips.htm "Melandre" wrote in message ... Recap: Recently, boat started overheating for approx. 2 to 4 minutes after startup. Temp goes to 220+F then it suddenly drops back to 150F and stays there, then all is fine until I get to my destination. The obvious culprit (I thought) was a faulty, sticky thermostat. I figured the thermostat simply does not open when it is supposed to (at approx. 160F) but eventually it does and the water cooling happens. Bought a new thermostat and replaced: no luck. Removed the thermostat entirely, closed the housing and started the boat: needle creeped up to 200+! Went home and tested both (old and new) thermostat in hot water: both appear to open at around 160F. So, it appears the problem is NOT the thermostat. I also disconnected the hose from the transom to the thermostat housing (the one drawing the water from the ocean). Started the boat for a few seconds and got a good flow so apparently no clogged intake either. I am assuming that water was pushed through by the impeller so that would mean the impeller is also doing its job (although I have actually not looked in there and impeller was replaced 2 months ago).. Now what? I am not sure what else to check. The alternator belt seems tight so I am also assuming the water pump is running at the correct speed (but I don't really know). In the manual, they list the typical symptoms of overheating (loose belt, clogged intakes, bad hoses, defective thermostat, worn or damaged stern drive water pump). Pretty much the stuff discussed above but also a couple that I have no clue what they are talking about: a) Excessively advanced or retarded ignition timing (????) b) Leakage of air or exhaust into the suction side of the stern water pump (????) I am not very mechanically inclined so I get lost quickly in the jargon. Anyone can offer suggestions, advices, comments, recommendations? I am getting desperate! Problem is I have a cabin that is boat-access only so no boat = stay home instead of enjoying a gorgeous weekend at the cabin... :( Andre |
It's also possible you have something really weird wrong with the
engine. Like a head gasket leak that allows combustion gasses to air-lock the cooling water flow. As the engine warms up, thermal expansion causes the leak to stop, and the system returns to normal. Just a thought. JR Melandre wrote: It takes a couple of minutes to get passed "normal temperature". Then another minute or so to climb over 200F. Then stays hot for 1 to 3 minutes (in a few occasions a bit longer than 3 minutes), then it drops back from well over 200F to 150F in about 3 - 5 seconds. I am not sure what you mean by "sending unit" but if you suggests that perhaps only the readout on the dashboard is screwed up, I doubt it because, for these few freaky minutes, I can really tell the engine is overheating (burning oil smell, block starts smoking a bit). Or maybe you are referring to yet another part that I am not aware of... It is also a simple raw water cooling system (not a closed one with coolant). Andre On 19 Aug 2005 22:15:49 -0700, wrote: Melandre wrote: Recap: Recently, boat started overheating for approx. 2 to 4 minutes after startup. Temp goes to 220+F then it suddenly drops back to 150F and stays there, then all is fine until I get to my destination. The obvious culprit (I thought) was a faulty, sticky thermostat. I figured the thermostat simply does not open when it is supposed to (at approx. 160F) but eventually it does and the water cooling happens. Bought a new thermostat and replaced: no luck. Removed the thermostat entirely, closed the housing and started the boat: needle creeped up to 200+! Went home and tested both (old and new) thermostat in hot water: both appear to open at around 160F. So, it appears the problem is NOT the thermostat. I also disconnected the hose from the transom to the thermostat housing (the one drawing the water from the ocean). Started the boat for a few seconds and got a good flow so apparently no clogged intake either. I am assuming that water was pushed through by the impeller so that would mean the impeller is also doing its job (although I have actually not looked in there and impeller was replaced 2 months ago).. Now what? I am not sure what else to check. The alternator belt seems tight so I am also assuming the water pump is running at the correct speed (but I don't really know). In the manual, they list the typical symptoms of overheating (loose belt, clogged intakes, bad hoses, defective thermostat, worn or damaged stern drive water pump). Pretty much the stuff discussed above but also a couple that I have no clue what they are talking about: a) Excessively advanced or retarded ignition timing (????) b) Leakage of air or exhaust into the suction side of the stern water pump (????) I am not very mechanically inclined so I get lost quickly in the jargon. Anyone can offer suggestions, advices, comments, recommendations? I am getting desperate! Problem is I have a cabin that is boat-access only so no boat = stay home instead of enjoying a gorgeous weekend at the cabin... :( Andre Aha. Depending on the accuracy of your description...... How fast does the temp climb to 220-250. Within 2 minutes or so after startup? How "suddenly" does it drop from 220 to 150? Your coolant will only cool so fast, so if it seems unnaturally quick it could be as simple as the sending unit. Since the thermostats passed the candy thermometer test, you know you have one good one and one spare. Sending unit is probably less expensive than a lot of other things you could fiddle around replacing, and if the temperature is changing by radical amounts in very short periods of time it is a reasonable suspect. -- -------------------------------------------------------------- Home Page: http://www.seanet.com/~jasonrnorth |
Melandre wrote: It takes a couple of minutes to get passed "normal temperature". Then another minute or so to climb over 200F. Then stays hot for 1 to 3 minutes (in a few occasions a bit longer than 3 minutes), then it drops back from well over 200F to 150F in about 3 - 5 seconds. We can be very certain that the cooling system isn't actually dropping in temp for over 200F to 150F in 3-5 seconds. If you're getting a report of a condition that seems virtually impossible, one of the first things to check is the data itself. You sending unit is almost certainly a screw-in unit with a wire attached to it. A new one would be very inexpensive. I am not sure what you mean by "sending unit" but if you suggests that perhaps only the readout on the dashboard is screwed up, I doubt it because, for these few freaky minutes, I can really tell the engine is overheating (burning oil smell, block starts smoking a bit). Or maybe you are referring to yet another part that I am not aware of... It is also a simple raw water cooling system (not a closed one with coolant). Andre |
I been in the auto repair industry and have yet to come by a headgasket that
would seal up when heated. But I guess there is always a first. "JR North" wrote in message ... It's also possible you have something really weird wrong with the engine. Like a head gasket leak that allows combustion gasses to air-lock the cooling water flow. As the engine warms up, thermal expansion causes the leak to stop, and the system returns to normal. Just a thought. JR Melandre wrote: It takes a couple of minutes to get passed "normal temperature". Then another minute or so to climb over 200F. Then stays hot for 1 to 3 minutes (in a few occasions a bit longer than 3 minutes), then it drops back from well over 200F to 150F in about 3 - 5 seconds. I am not sure what you mean by "sending unit" but if you suggests that perhaps only the readout on the dashboard is screwed up, I doubt it because, for these few freaky minutes, I can really tell the engine is overheating (burning oil smell, block starts smoking a bit). Or maybe you are referring to yet another part that I am not aware of... It is also a simple raw water cooling system (not a closed one with coolant). Andre On 19 Aug 2005 22:15:49 -0700, wrote: Melandre wrote: Recap: Recently, boat started overheating for approx. 2 to 4 minutes after startup. Temp goes to 220+F then it suddenly drops back to 150F and stays there, then all is fine until I get to my destination. The obvious culprit (I thought) was a faulty, sticky thermostat. I figured the thermostat simply does not open when it is supposed to (at approx. 160F) but eventually it does and the water cooling happens. Bought a new thermostat and replaced: no luck. Removed the thermostat entirely, closed the housing and started the boat: needle creeped up to 200+! Went home and tested both (old and new) thermostat in hot water: both appear to open at around 160F. So, it appears the problem is NOT the thermostat. I also disconnected the hose from the transom to the thermostat housing (the one drawing the water from the ocean). Started the boat for a few seconds and got a good flow so apparently no clogged intake either. I am assuming that water was pushed through by the impeller so that would mean the impeller is also doing its job (although I have actually not looked in there and impeller was replaced 2 months ago).. Now what? I am not sure what else to check. The alternator belt seems tight so I am also assuming the water pump is running at the correct speed (but I don't really know). In the manual, they list the typical symptoms of overheating (loose belt, clogged intakes, bad hoses, defective thermostat, worn or damaged stern drive water pump). Pretty much the stuff discussed above but also a couple that I have no clue what they are talking about: a) Excessively advanced or retarded ignition timing (????) b) Leakage of air or exhaust into the suction side of the stern water pump (????) I am not very mechanically inclined so I get lost quickly in the jargon. Anyone can offer suggestions, advices, comments, recommendations? I am getting desperate! Problem is I have a cabin that is boat-access only so no boat = stay home instead of enjoying a gorgeous weekend at the cabin... :( Andre Aha. Depending on the accuracy of your description...... How fast does the temp climb to 220-250. Within 2 minutes or so after startup? How "suddenly" does it drop from 220 to 150? Your coolant will only cool so fast, so if it seems unnaturally quick it could be as simple as the sending unit. Since the thermostats passed the candy thermometer test, you know you have one good one and one spare. Sending unit is probably less expensive than a lot of other things you could fiddle around replacing, and if the temperature is changing by radical amounts in very short periods of time it is a reasonable suspect. -- -------------------------------------------------------------- Home Page: http://www.seanet.com/~jasonrnorth |
Is it possible that you are getting an air gap in the engine ? Without
water in the cooling channels the motor will heat up fast and cool quickly one the thermostat opens and you get water flowing. Check the water outlet for bubbles when starting the engine. |
Another two possibilities. I'm not clear whether you have a sal****er
cooling system or a heat exchanger system. If you have raw water cooling one possibility is rust flakes in the passages in the head. I've seen heads and heat exchangers plugged almost solid. This likely wouldn't be the case if your temp drops back to normal. But keep it in mind if the engine is raw water cooled and hasn't been checked or cleaned for a while. The other possibility is that you have an airlock in the system. Maybe a looped water hose or something like that? Don "Melandre" wrote in message ... Recap: Recently, boat started overheating for approx. 2 to 4 minutes after startup. Temp goes to 220+F then it suddenly drops back to 150F and stays there, then all is fine until I get to my destination. The obvious culprit (I thought) was a faulty, sticky thermostat. I figured the thermostat simply does not open when it is supposed to (at approx. 160F) but eventually it does and the water cooling happens. Bought a new thermostat and replaced: no luck. Removed the thermostat entirely, closed the housing and started the boat: needle creeped up to 200+! Went home and tested both (old and new) thermostat in hot water: both appear to open at around 160F. So, it appears the problem is NOT the thermostat. I also disconnected the hose from the transom to the thermostat housing (the one drawing the water from the ocean). Started the boat for a few seconds and got a good flow so apparently no clogged intake either. I am assuming that water was pushed through by the impeller so that would mean the impeller is also doing its job (although I have actually not looked in there and impeller was replaced 2 months ago).. Now what? I am not sure what else to check. The alternator belt seems tight so I am also assuming the water pump is running at the correct speed (but I don't really know). In the manual, they list the typical symptoms of overheating (loose belt, clogged intakes, bad hoses, defective thermostat, worn or damaged stern drive water pump). Pretty much the stuff discussed above but also a couple that I have no clue what they are talking about: a) Excessively advanced or retarded ignition timing (????) b) Leakage of air or exhaust into the suction side of the stern water pump (????) I am not very mechanically inclined so I get lost quickly in the jargon. Anyone can offer suggestions, advices, comments, recommendations? I am getting desperate! Problem is I have a cabin that is boat-access only so no boat = stay home instead of enjoying a gorgeous weekend at the cabin... :( Andre |
wrote in message ups.com... Melandre wrote: It takes a couple of minutes to get passed "normal temperature". Then another minute or so to climb over 200F. Then stays hot for 1 to 3 minutes (in a few occasions a bit longer than 3 minutes), then it drops back from well over 200F to 150F in about 3 - 5 seconds. We can be very certain that the cooling system isn't actually dropping in temp for over 200F to 150F in 3-5 seconds. If you're getting a report of a condition that seems virtually impossible, one of the first things to check is the data itself. You sending unit is almost certainly a screw-in unit with a wire attached to it. A new one would be very inexpensive. In a RAW water system that has no water flow it can overheat fairly fast and the sending unit will show the increased temp, if the water suddenly starts flowing the sending unit gets very cool raw water running over it almost immediately and it cools down FAST. In fresh water /heat exchanger systems the temp of the coolant in the engine can't cool down as fast. I'd check for a kink in the hose in the outdrive. There is a service note on Merc outdrives about this problem. |
Quick update for those (and thanks to all for feedback so far!) who are
following this tread. Spent Sunday afternoon at the marina still trying to diagnose the source of the overheating problem. First I disconnected the hose coming from the transom/leg and going to the thermostat housing: I started the boat and saw a really good flow of water coming out of the hose. To me, this would indicate that the raw pickup of water on the stern drive is not plugged and the two-month old impeller appears to be pushing water through the hose as it should. Then I pretty much disconnected, sequencially, all cooling related hoses going in to and coming out from the engine block. A flow of water could be seen although I do not know if this flow was normal or lower than what it should be. The only place that I did not check is where the hose re-enters the thermostat housing and presumably find its way to the manifold/riser and then out. So if I am still thinking blockage, this may be one more place to look: is it easy to remove the riser cover? With blockage or clogging being a less likely cause, I am once again looking for other culprits. Again, restating that I am not very mechanically inclined, I am starting to think that my problem may be related to a defective water pump (not the stern drive (impeller) one but the "engine-circulating" water pump (the one that is spun by the alternator belt I believe). I see no physical evidence of a defective or clogged water pump but if that water pump was not turning properly (sliding or whatever) or if it was clogged or defective (but not 100% broken), could it explain why when I get on my way and increase RPM, the problem seems to eventually fixed itself (cooling process starts, needle drops to 150F and all is well). Perhaps, there is a point where the water pump turns "enough" to enable the cooling process to happen? Could this explain why the overheating appears to happen primarily at idle or low speed? When the boat runs at idle for the first 5 minutes (until the needle creeps to 200F+) the boat sounds good. No weird or clinging noise or whatever. As far as I can tell, oil in the engine block is clean (although I admit I am not sure I would be able to see the difference if there was water in it - unless it is very obvious). So I am thinking/praying that I may not have a major problem yet and that the problem may still reside within the (raw) cooling system itself. Any comment, advice, suggestion regarding probability of a clogged manifold/riser or the possibility of having a defective engine-circulating water pump (even though no external sign of it not working properly)? Sorry for the long post! Andre PS: yes, I recognize (and regret!) my lack of mechanical knowledge and yes, I am looking for the service of a boat mechanic to help me out. However, they unfortunately all seem pretty busy at the moment! |
On 23 Aug 2005 11:53:20 -0700, "Melandre" wrote:
Quick update for those (and thanks to all for feedback so far!) who are following this tread. Spent Sunday afternoon at the marina still trying to diagnose the source of the overheating problem. First I disconnected the hose coming from the transom/leg and going to the thermostat housing: I started the boat and saw a really good flow of water coming out of the hose. To me, this would indicate that the raw pickup of water on the stern drive is not plugged and the two-month old impeller appears to be pushing water through the hose as it should. Then I pretty much disconnected, sequencially, all cooling related hoses going in to and coming out from the engine block. A flow of water could be seen although I do not know if this flow was normal or lower than what it should be. The only place that I did not check is where the hose re-enters the thermostat housing and presumably find its way to the manifold/riser and then out. So if I am still thinking blockage, this may be one more place to look: is it easy to remove the riser cover? With blockage or clogging being a less likely cause, I am once again looking for other culprits. Again, restating that I am not very mechanically inclined, I am starting to think that my problem may be related to a defective water pump (not the stern drive (impeller) one but the "engine-circulating" water pump (the one that is spun by the alternator belt I believe). I see no physical evidence of a defective or clogged water pump but if that water pump was not turning properly (sliding or whatever) or if it was clogged or defective (but not 100% broken), could it explain why when I get on my way and increase RPM, the problem seems to eventually fixed itself (cooling process starts, needle drops to 150F and all is well). Perhaps, there is a point where the water pump turns "enough" to enable the cooling process to happen? Could this explain why the overheating appears to happen primarily at idle or low speed? When the boat runs at idle for the first 5 minutes (until the needle creeps to 200F+) the boat sounds good. No weird or clinging noise or whatever. As far as I can tell, oil in the engine block is clean (although I admit I am not sure I would be able to see the difference if there was water in it - unless it is very obvious). So I am thinking/praying that I may not have a major problem yet and that the problem may still reside within the (raw) cooling system itself. Any comment, advice, suggestion regarding probability of a clogged manifold/riser or the possibility of having a defective engine-circulating water pump (even though no external sign of it not working properly)? Sorry for the long post! Andre PS: yes, I recognize (and regret!) my lack of mechanical knowledge and yes, I am looking for the service of a boat mechanic to help me out. However, they unfortunately all seem pretty busy at the moment! Removing a riser is not that big a deal. Just have new gaskets and sealant ready when you reinstall. I'd consider replacing the bolts and nuts also and put some anti-seize on them for next time. Have you checked the tension of your belt? I'd definitely look there, and perhaps replace the belt, which could be old and slipping. I'm on my third circulation pump. The first lost a seal, and the second lost a bearing due to an overtight belt (IMHO). The mechanic who installed the circulating pump was fired shortly after doing the work, so I doubt how well he checked the belt tension. Now I know to check it myself. -- John H. On the 'PocoLoco' out of Deale, MD |
There should be a bypass port in your thermostat housing to cool the exhaust
when the thermostat is closed. This port may be blocked. JIMinFL "Melandre" wrote in message ups.com... Quick update for those (and thanks to all for feedback so far!) who are following this tread. Spent Sunday afternoon at the marina still trying to diagnose the source of the overheating problem. First I disconnected the hose coming from the transom/leg and going to the thermostat housing: I started the boat and saw a really good flow of water coming out of the hose. To me, this would indicate that the raw pickup of water on the stern drive is not plugged and the two-month old impeller appears to be pushing water through the hose as it should. Then I pretty much disconnected, sequencially, all cooling related hoses going in to and coming out from the engine block. A flow of water could be seen although I do not know if this flow was normal or lower than what it should be. The only place that I did not check is where the hose re-enters the thermostat housing and presumably find its way to the manifold/riser and then out. So if I am still thinking blockage, this may be one more place to look: is it easy to remove the riser cover? With blockage or clogging being a less likely cause, I am once again looking for other culprits. Again, restating that I am not very mechanically inclined, I am starting to think that my problem may be related to a defective water pump (not the stern drive (impeller) one but the "engine-circulating" water pump (the one that is spun by the alternator belt I believe). I see no physical evidence of a defective or clogged water pump but if that water pump was not turning properly (sliding or whatever) or if it was clogged or defective (but not 100% broken), could it explain why when I get on my way and increase RPM, the problem seems to eventually fixed itself (cooling process starts, needle drops to 150F and all is well). Perhaps, there is a point where the water pump turns "enough" to enable the cooling process to happen? Could this explain why the overheating appears to happen primarily at idle or low speed? When the boat runs at idle for the first 5 minutes (until the needle creeps to 200F+) the boat sounds good. No weird or clinging noise or whatever. As far as I can tell, oil in the engine block is clean (although I admit I am not sure I would be able to see the difference if there was water in it - unless it is very obvious). So I am thinking/praying that I may not have a major problem yet and that the problem may still reside within the (raw) cooling system itself. Any comment, advice, suggestion regarding probability of a clogged manifold/riser or the possibility of having a defective engine-circulating water pump (even though no external sign of it not working properly)? Sorry for the long post! Andre PS: yes, I recognize (and regret!) my lack of mechanical knowledge and yes, I am looking for the service of a boat mechanic to help me out. However, they unfortunately all seem pretty busy at the moment! |
"Melandre" wrote in message ups.com... Quick update for those (and thanks to all for feedback so far!) who are following this tread. Spent Sunday afternoon at the marina still trying to diagnose the source of the overheating problem. First I disconnected the hose coming from the transom/leg and going to the thermostat housing: I started the boat and saw a really good flow of water coming out of the hose. To me, this would indicate that the raw pickup of water on the stern drive is not plugged and the two-month old impeller appears to be pushing water through the hose as it should. Then I pretty much disconnected, sequencially, all cooling related hoses going in to and coming out from the engine block. A flow of water could be seen although I do not know if this flow was normal or lower than what it should be. The only place that I did not check is where the hose re-enters the thermostat housing and presumably find its way to the manifold/riser and then out. So if I am still thinking blockage, this may be one more place to look: is it easy to remove the riser cover? With blockage or clogging being a less likely cause, I am once again looking for other culprits. Again, restating that I am not very mechanically inclined, I am starting to think that my problem may be related to a defective water pump (not the stern drive (impeller) one but the "engine-circulating" water pump (the one that is spun by the alternator belt I believe). I see no physical evidence of a defective or clogged water pump but if that water pump was not turning properly (sliding or whatever) or if it was clogged or defective (but not 100% broken), could it explain why when I get on my way and increase RPM, the problem seems to eventually fixed itself (cooling process starts, needle drops to 150F and all is well). Perhaps, there is a point where the water pump turns "enough" to enable the cooling process to happen? Could this explain why the overheating appears to happen primarily at idle or low speed? When the boat runs at idle for the first 5 minutes (until the needle creeps to 200F+) the boat sounds good. No weird or clinging noise or whatever. As far as I can tell, oil in the engine block is clean (although I admit I am not sure I would be able to see the difference if there was water in it - unless it is very obvious). So I am thinking/praying that I may not have a major problem yet and that the problem may still reside within the (raw) cooling system itself. Any comment, advice, suggestion regarding probability of a clogged manifold/riser or the possibility of having a defective engine-circulating water pump (even though no external sign of it not working properly)? Sorry for the long post! Andre PS: yes, I recognize (and regret!) my lack of mechanical knowledge and yes, I am looking for the service of a boat mechanic to help me out. However, they unfortunately all seem pretty busy at the moment! I've found a quick and dirty method of finding where the problem is in a raw water cooling system. Provided that the impeller is good, squeeze the hose and see if it's tighter/stiffer when the impeller/engine is running. If it gets stiffer then there is blockage downflow from that point. |
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