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#1
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INDMAR Engine (Corvette LT1) Overheating - advice please
Hello
New to the group, hoping to find someone with some knowledge to help me fix an issue i am having with my boats motor. Apologies for the long post, but for those who like a problem, i am sure you will enjoy! Details as follows: INDMAR LT1 V8 Corvette motor - 1997 make, 500 running hours. SYMPTOMS: - Once the engine has been operating for at least 20 minutes, when brought up to cruising speed from a standing start (such as pulling up a skier) when the engine is under load, the engine temp rises rapidly from 150F (normal operating temp) to ~200F when the management takes over and shuts down the motor. - The temp can be brought back to normal (equally as rapidly - nearly instantaneously! which i know is not good for anything) by a quick "blip" of the throttle, which appears to restart the cooling. - The problem does not happen at any speed if the engine is not put under excessive load, ie, i can run it at WOT with no problem so long as i take it there slowly. WHAT IT IS NOT! I have been over the cooling system and checked / replaced the following parts, none of these have fixed the problem. - Raw water impeller,replaced (was due anyway), not the problem, good water flow - Raw water thermostat, replaced also ran without, not the problem - Cooling circuit, does not appear to have any blockages - Engine side thermostat, replaced, not the problem, Ran without, NOT OVERHEATING but runs too cold, as expected (~110F), and the EFI management stays in cold start calibration - Water pump, replaced, was squeaking, thought it could be sucking air through the bearing (cam driven not belt), did not fix the problem although the engine doesn't squeak anymore! (have to take the good with the bad!) WHAT I THINK THE PROBLEM MAY BE I think i may have done a head gasket. But i am open to other suggestions from anyone who may have a bit more knowledge on the engines. I figure water is pouring into the exhaust (or exhaust into the water) when the engine is under load, creating a hot air pocket under the engine side thermostat which is preventing it from opening and causing the problem. Potentially it is only when under load that this seal is "blowing out", which is why i can run all day so long as i take her to speed slowly. There are no other leaks, could the cooling circuit be sucking air from anywhere else? CAN YOU HELP?? (PLEASE!) Before heading down the track of tearing the engine apart, i am hoping that i could get some comment on my "diagnosis" and any other potential problems i may have missed. Also keen for some advice on the following: - Is there any way to confirm this (given that it is an intermittent) prior to pulling the engine apart? Especially with relation to which cylinder bank has the problem. - Although i do know the common sense answer to this question, am i likely to do the engine any harm running without a thermostat (other than running a bit rich on cool start calibration) to keep the engine cool and not putting it under load. For various reasons, ideally i need to get a few hours out of the engine before i can get this maintenance done. Apologies for the long post. This problem has stumped at least half a dozen marine mechs over here (Australia) and i am keen for resolution. Cheers Michael S |
#2
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INDMAR Engine (Corvette LT1) Overheating - advice please
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#3
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INDMAR Engine (Corvette LT1) Overheating - advice please
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#4
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INDMAR Engine (Corvette LT1) Overheating - advice please
On Jan 18, 4:28*pm, wrote:
Hello New to the group, hoping to find someone with some knowledge to help me fix an issue i am having with my boats motor. Apologies for the long post, but for those who like a problem, i am sure you will enjoy! Details as follows: INDMAR LT1 V8 Corvette motor - 1997 make, 500 running hours. SYMPTOMS: - Once the engine has been operating for at least 20 minutes, when brought up to cruising speed from a standing start (such as pulling up a skier) when the engine is under load, the engine temp rises rapidly from 150F (normal operating temp) to ~200F when the management takes over and shuts down the motor. - The temp can be brought back to normal (equally as rapidly - nearly instantaneously! which i know is not good for anything) *by a quick "blip" of the throttle, which appears to restart the cooling. - The problem does not happen at any speed if the engine is not put under excessive load, ie, i can run it at WOT with no problem so long as i take it there slowly. WHAT IT IS NOT! I have been over the cooling system and checked / replaced the following parts, none of these have fixed the problem. - Raw water impeller,replaced (was due anyway), not the problem, good water flow - Raw water thermostat, replaced also ran without, not the problem - Cooling circuit, does not appear to have any blockages - Engine side thermostat, replaced, not the problem, Ran without, NOT OVERHEATING but runs too cold, as expected (~110F), and the EFI management stays in cold start calibration - Water pump, replaced, was squeaking, thought it could be sucking air through the bearing (cam driven not belt), did not fix the problem although the engine doesn't squeak anymore! (have to take the good with the bad!) WHAT I THINK THE PROBLEM MAY BE I think i may have done a head gasket. But i am open to other suggestions from anyone who may have a bit more knowledge on the engines. I figure water is pouring into the exhaust (or exhaust into the water) when the engine is under load, creating a hot air pocket under the engine side thermostat which is preventing it from opening and causing the problem. Potentially it is only when under load that this seal is "blowing out", which is why i can run all day so long as i take her to speed slowly. There are no other leaks, could the cooling circuit be sucking air from anywhere else? CAN YOU HELP?? (PLEASE!) Before heading down the track of tearing the engine apart, i am hoping that i could get some comment on my "diagnosis" and any other potential problems i may have missed. Also keen for some advice on the following: - Is there any way to confirm this (given that it is an intermittent) prior to pulling the engine apart? Especially with relation to which cylinder bank has the problem. - Although i do know the common sense answer to this question, am i likely to do the engine any harm running without a thermostat (other than running a bit rich on cool start calibration) to keep the engine cool and not putting it under load. For various reasons, ideally i need to get a few hours out of the engine before i can get this maintenance done. Apologies for the long post. This problem has stumped at least half a dozen marine mechs over here (Australia) and i am keen for resolution. Cheers Michael S Michael, No problem for the long post. i take it you have a mercruiser outdrive? I noticed you mentioned that you cahanged the impeller. Did you use a genuine mfj. part? The reason I say is because a friend of mine had an overheat problem with a later model 2 cycle mercury 200 hp. The impeller was getting bad. so they changed it and had the same problem, ao they took it to the local mercury doctor,a nd he did a flow on it and it was up to spec at idle. but when the engine rpm was raised to a certain RPM the heat alarm started sending off. He dropped the lower and found they had installed the impeller correctly, however they used a cheap EBay par. and even though new and liked identical, the mechanic explained to them that the aftermarket part had too soft of a rubber composite, and when a certain RPM was achieved, the vanes were literally folding back away from the impeller housing and wasn't able to pump water up to the engine. He replaced the impeller with an OE Quicksilver part, and problem cured. Just something to consider. |
#5
posted to rec.boats
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INDMAR Engine (Corvette LT1) Overheating - advice please
On Sun, 18 Jan 2009 22:46:24 -0500, Jim7492383432
wrote: wrote: Hello New to the group, hoping to find someone with some knowledge to help me fix an issue i am having with my boats motor. Apologies for the long post, but for those who like a problem, i am sure you will enjoy! Details as follows: INDMAR LT1 V8 Corvette motor - 1997 make, 500 running hours. SYMPTOMS: - Once the engine has been operating for at least 20 minutes, when brought up to cruising speed from a standing start (such as pulling up a skier) when the engine is under load, the engine temp rises rapidly from 150F (normal operating temp) to ~200F when the management takes over and shuts down the motor. - The temp can be brought back to normal (equally as rapidly - nearly instantaneously! which i know is not good for anything) by a quick "blip" of the throttle, which appears to restart the cooling. - The problem does not happen at any speed if the engine is not put under excessive load, ie, i can run it at WOT with no problem so long as i take it there slowly. WHAT IT IS NOT! I have been over the cooling system and checked / replaced the following parts, none of these have fixed the problem. - Raw water impeller,replaced (was due anyway), not the problem, good water flow - Raw water thermostat, replaced also ran without, not the problem - Cooling circuit, does not appear to have any blockages - Engine side thermostat, replaced, not the problem, Ran without, NOT OVERHEATING but runs too cold, as expected (~110F), and the EFI management stays in cold start calibration - Water pump, replaced, was squeaking, thought it could be sucking air through the bearing (cam driven not belt), did not fix the problem although the engine doesn't squeak anymore! (have to take the good with the bad!) WHAT I THINK THE PROBLEM MAY BE I think i may have done a head gasket. But i am open to other suggestions from anyone who may have a bit more knowledge on the engines. I figure water is pouring into the exhaust (or exhaust into the water) when the engine is under load, creating a hot air pocket under the engine side thermostat which is preventing it from opening and causing the problem. Potentially it is only when under load that this seal is "blowing out", which is why i can run all day so long as i take her to speed slowly. There are no other leaks, could the cooling circuit be sucking air from anywhere else? CAN YOU HELP?? (PLEASE!) Before heading down the track of tearing the engine apart, i am hoping that i could get some comment on my "diagnosis" and any other potential problems i may have missed. Also keen for some advice on the following: - Is there any way to confirm this (given that it is an intermittent) prior to pulling the engine apart? Especially with relation to which cylinder bank has the problem. - Although i do know the common sense answer to this question, am i likely to do the engine any harm running without a thermostat (other than running a bit rich on cool start calibration) to keep the engine cool and not putting it under load. For various reasons, ideally i need to get a few hours out of the engine before i can get this maintenance done. Apologies for the long post. This problem has stumped at least half a dozen marine mechs over here (Australia) and i am keen for resolution. Cheers Michael S Check suction side of water pump for air leak, obstruction, collapsing hose. Check exhaust for blockage. Gaskets wear plates and seals in water pump may need replacing. That's what I was thinking to check first. No sense assuming a head gasket and doing unnecessary work when there's cooling system stuff to check out. That "blipping" of the throttle cooling it down might be a clue pointing at a collapsed hose, or some change in boat attitude affecting the inlet stream. Can you get pressure gage on these raw water systems? --Vic |
#6
posted to rec.boats
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INDMAR Engine (Corvette LT1) Overheating - advice please
Are you certain the engine really is overheating? I'd probably also try to
figure out if I could check the efi operation. After a hard run with it overheating pull the plugs and take a look at them. Lean fuel could be causing it if it's not a cooling system problem. That would also explain why it doesn't happen when the system is stuck in cold start mode. If it is the cooling system it sounds like maybe an obstruction. The fact that you can run it at wot for extended periods also suggests something is happening when you pull up a skier or launch hard. A long wot run is just as much load as pulling up a skier. Unfortunately the hard start could be causing your temporary obstruction or detonation from a fuel management issue though. I would not expect it to be head gaskets "temporarily" failing. My experience with head gaskets is that once they fail that's it they are shot. Once a cylinder breaks thru a gasket it burns it thru. There is a steel ring around the cylinder. Behind that it's pretty much regular gasket material. The system should be able to handle air. I'm assuming it's a raw water system? You can test you air pocket theory by drilling a small hole in the thermostat thru the plate where it will always pass a little air/water. wrote in message ... Hello New to the group, hoping to find someone with some knowledge to help me fix an issue i am having with my boats motor. Apologies for the long post, but for those who like a problem, i am sure you will enjoy! Details as follows: INDMAR LT1 V8 Corvette motor - 1997 make, 500 running hours. SYMPTOMS: - Once the engine has been operating for at least 20 minutes, when brought up to cruising speed from a standing start (such as pulling up a skier) when the engine is under load, the engine temp rises rapidly from 150F (normal operating temp) to ~200F when the management takes over and shuts down the motor. - The temp can be brought back to normal (equally as rapidly - nearly instantaneously! which i know is not good for anything) by a quick "blip" of the throttle, which appears to restart the cooling. - The problem does not happen at any speed if the engine is not put under excessive load, ie, i can run it at WOT with no problem so long as i take it there slowly. WHAT IT IS NOT! I have been over the cooling system and checked / replaced the following parts, none of these have fixed the problem. - Raw water impeller,replaced (was due anyway), not the problem, good water flow - Raw water thermostat, replaced also ran without, not the problem - Cooling circuit, does not appear to have any blockages - Engine side thermostat, replaced, not the problem, Ran without, NOT OVERHEATING but runs too cold, as expected (~110F), and the EFI management stays in cold start calibration - Water pump, replaced, was squeaking, thought it could be sucking air through the bearing (cam driven not belt), did not fix the problem although the engine doesn't squeak anymore! (have to take the good with the bad!) WHAT I THINK THE PROBLEM MAY BE I think i may have done a head gasket. But i am open to other suggestions from anyone who may have a bit more knowledge on the engines. I figure water is pouring into the exhaust (or exhaust into the water) when the engine is under load, creating a hot air pocket under the engine side thermostat which is preventing it from opening and causing the problem. Potentially it is only when under load that this seal is "blowing out", which is why i can run all day so long as i take her to speed slowly. There are no other leaks, could the cooling circuit be sucking air from anywhere else? CAN YOU HELP?? (PLEASE!) Before heading down the track of tearing the engine apart, i am hoping that i could get some comment on my "diagnosis" and any other potential problems i may have missed. Also keen for some advice on the following: - Is there any way to confirm this (given that it is an intermittent) prior to pulling the engine apart? Especially with relation to which cylinder bank has the problem. - Although i do know the common sense answer to this question, am i likely to do the engine any harm running without a thermostat (other than running a bit rich on cool start calibration) to keep the engine cool and not putting it under load. For various reasons, ideally i need to get a few hours out of the engine before i can get this maintenance done. Apologies for the long post. This problem has stumped at least half a dozen marine mechs over here (Australia) and i am keen for resolution. Cheers Michael S |
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