Hi all,

Recently I asked for advice here on my 79 Yanmar 2QM15. Based on advice
here I had the head gasket replaced. A shop inspected the head, but
didn't Xray it, or whatever it is they do. The guy who replaced the head
gasket is apparently at the limit of his abilities, so my next plan is
to have it looked at by a shop. I was hoping I could get some good clues
from the diesel experts here first.

I'm not sure how long the problem I am about to describe has existed but
there may have been versions of the problem present since I bought the
boat a year ago. It has been somewhat intermittent, but seems worse
since the head gasket replacement.

The motor starts hard, but instantly with a squirt of starter fluid. It
runs with a knock at almost all RPMs, but no knock at full throttle with
a little black smoke. After about 5-10 minutes, the power drastically
decreases. It will keep running in neutral, purring like a kitten at all
RPMs, however a fair amount of black fluid pours out of the exhaust, to
float on the water, not much smoke.

Any ideas?

Stephen

In article ,
Stephen Trapani wrote:

The motor starts hard, but instantly with a squirt of starter fluid. It
runs with a knock at almost all RPMs, but no knock at full throttle with
a little black smoke. After about 5-10 minutes, the power drastically
decreases. It will keep running in neutral, purring like a kitten at all
RPMs, however a fair amount of black fluid pours out of the exhaust, to
float on the water, not much smoke.

Sounds like low compression (hard starting) and injector mis-timing.

The black fluid is simply dissolved soot, which could indicate the need
for at least resetting valve clearances when you're not pulling
significant power. Could also mean a burnt valve. Either could cause
hard starting.

Looking again, the new head gasket would require readjusting the valves,
so make sure that's been done.

Using starter fluid is dangerous.

The hard starts could also be from undersized battery or cables, or
slightly corroded connections. We have 1/0 and 2/0 cable runs of less
than 6' and can start with 11 volts. When we had smaller and longer
cables, it took at least 12v when everything was clean and tight. Years
ago, my car wouldn't start due to an extra ohm or two resistance in a
cable connector. Simply squeezing the connector in a vise fixed it for
almost 15 years (Mom's car).

The drastic power decrease after a few minutes could be a mostly-blocked
fuel filter, fuel tank pickup or vent. Change filters, clean the bowls
and see if it still happens. Then open the fuel fill. If still no joy,
pull the pickup out of the tank and see if there's a screen at the
bottom. Remove if there is. Once, I had so many dead critters in the
tank that a straight tube clogged. Siphoned the fuel out of the tank
through a Baja filter (West Marine has a good variant) to give the
filters a break. Luckily, we had less than 5 gallons onboard at the time.

I'd also suspect overheating at full power, except that the alarms
aren't going off. Any change in the reservoir level, day to day?

If those steps don't solve it, I'm afraid you're looking at a rebuild,
but don't start worrying until you've exhausted alternatives, as that's
a remarkable engine from what I've heard.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

Jere Lull wrote:

In article ,
Stephen Trapani wrote:


The motor starts hard, but instantly with a squirt of starter fluid. It
runs with a knock at almost all RPMs, but no knock at full throttle with
a little black smoke. After about 5-10 minutes, the power drastically
decreases. It will keep running in neutral, purring like a kitten at all
RPMs, however a fair amount of black fluid pours out of the exhaust, to
float on the water, not much smoke.


Sounds like low compression (hard starting) and injector mis-timing.

The black fluid is simply dissolved soot, which could indicate the need
for at least resetting valve clearances when you're not pulling
significant power. Could also mean a burnt valve. Either could cause
hard starting.

Looking again, the new head gasket would require readjusting the valves,
so make sure that's been done.

Using starter fluid is dangerous.

The hard starts could also be from undersized battery or cables,

Yes, I have a low battery bank. Old batteries and it turns over fairly
slowly. Once the engine is warm, it starts in a second or two every time.

or
slightly corroded connections. We have 1/0 and 2/0 cable runs of less
than 6' and can start with 11 volts. When we had smaller and longer
cables, it took at least 12v when everything was clean and tight. Years
ago, my car wouldn't start due to an extra ohm or two resistance in a
cable connector. Simply squeezing the connector in a vise fixed it for
almost 15 years (Mom's car).

The drastic power decrease after a few minutes could be a mostly-blocked
fuel filter, fuel tank pickup or vent. Change filters, clean the bowls
and see if it still happens.

I did this all once. Maybe the Racor needs changing? I had the tank all
the way out and cleaned by two mechanic friends.

Then open the fuel fill. If still no joy,
pull the pickup out of the tank and see if there's a screen at the
bottom.

I'm going to call him and ask about the screen at the bottom.... He says
no screen at the bottom.


Remove if there is. Once, I had so many dead critters in the
tank that a straight tube clogged. Siphoned the fuel out of the tank
through a Baja filter (West Marine has a good variant) to give the
filters a break. Luckily, we had less than 5 gallons onboard at the time.

I'd also suspect overheating at full power, except that the alarms
aren't going off. Any change in the reservoir level, day to day?

Reservoir?

If those steps don't solve it, I'm afraid you're looking at a rebuild,
but don't start worrying until you've exhausted alternatives, as that's
a remarkable engine from what I've heard.

Would a diesel needing a rebuild run hard for ten minutes, then lose RPM
and pushing power?

Stephen

In article ,
Stephen Trapani wrote:

Jere Lull wrote:

The hard starts could also be from undersized battery or cables,

Yes, I have a low battery bank. Old batteries and it turns over
fairly slowly. Once the engine is warm, it starts in a second or two
every time.

Work on that in any case. I would make sure the battery was well
charged and the connections clean and tight before at least one cold
start, to eliminate (or confirm) the starting circuit as a problem.

A warm engine will usually start more easily than a cold one, and a low
battery's charge will improve quickly. Thus, an easy warm start doesn't
help diagnose the problem much.

The drastic power decrease after a few minutes could be a
mostly-blocked fuel filter, fuel tank pickup or vent. Change
filters, clean the bowls and see if it still happens.

I did this all once. Maybe the Racor needs changing? I had the tank
all the way out and cleaned by two mechanic friends.

The one time I had critter problems, it didn't clear up until I'd
changed the filter twice and brushed off my last one once or twice.
Even then, we couldn't pull full power until we'd motored a few hours at
low power. Lots of critter corpses fell to the bottom of the bowl as
we slowly bounced along.

I'd also suspect overheating at full power, except that the alarms
aren't going off. Any change in the reservoir level, day to day?

Reservoir?

Sorry, I forgot that the 2QM15 was raw-water. I was trying to
figure out whether you might be overheating without the alarm going
off. You have water coming out the exhaust from your other posts,
so I tend to assume you aren't overheating in 10 minutes. Any sign/smell
of overheating as you lose power? Any little things that might not seem
important?

If those steps don't solve it, I'm afraid you're looking at a
rebuild, but don't start worrying until you've exhausted
alternatives, as that's a remarkable engine from what I've heard.

Would a diesel needing a rebuild run hard for ten minutes, then lose
RPM and pushing power?

I don't believe so. Most of the time, they seem to get cranky about
everything.

What you're describing sounds consistent and repeatable. What happens if
you're not pulling high power? Do you have a drop-off if you motor at
200, 400, ... fewer RPMs? If you do, does it take longer?

And about that drop-off: Does the engine die, or will it continue to run
at the lower power for a long time? How high is that lower power? For
that matter, what are the RPMs at high power?

As I write, I also wonder: Is the stuffing box hot when you get the
drop-off?

I still primarily suspect fuel delivery. If it's not the filter, than
possibly something that's binding when the engine gets up to operating
temperature.

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

Stephen Trapani wrote in
:

Any ideas?

Stephen



I assume it has a heat exchanger, not raw water cooling. Fill the fresh
water side with coolant. Leave the cap off the fresh water heat exchanger.
Start the engine and idle it until it warms up a little, but not hot. A
little coolant will naturally escape as it expands. Watch the level with
the cap off. See any massive bubbling, indicating there are hot gasses
escaping from the cylinders into the cooling passages in the head and
cylinder walls? This'll tell you if the head is cracked or is warped
enough to let gasses bypass the head gasket into the cooling system. Not
rocket science, but reliable. No computer is necessary...(c;

Also, note if the engine runs smoother with the pressure cap off it.
Sometimes small quantities of pressurized coolant squeeze their way into
the cylinder as it sucks in fresh air, compress and EXPLODE INTO STEAM
inside the cylinder head as the piston comes up over TDC, making a bad
knocking sound, too! Are you losing coolant for no apparent reason? This
may be why if you are.

Flush out the bilge with fresh water after midnight when the greenies
aren't watching to get the little coolant out of the bilge...(c;

No fun....

--
Larry

Larry wrote:

Stephen Trapani wrote in
:


Any ideas?

Stephen




I assume it has a heat exchanger, not raw water cooling.

It's raw water.

Fill the fresh
water side with coolant. Leave the cap off the fresh water heat exchanger.
Start the engine and idle it until it warms up a little, but not hot. A
little coolant will naturally escape as it expands. Watch the level with
the cap off. See any massive bubbling, indicating there are hot gasses
escaping from the cylinders into the cooling passages in the head and
cylinder walls? This'll tell you if the head is cracked or is warped
enough to let gasses bypass the head gasket into the cooling system. Not
rocket science, but reliable. No computer is necessary...(c;

Also, note if the engine runs smoother with the pressure cap off it.
Sometimes small quantities of pressurized coolant squeeze their way into
the cylinder as it sucks in fresh air, compress and EXPLODE INTO STEAM
inside the cylinder head as the piston comes up over TDC, making a bad
knocking sound, too! Are you losing coolant for no apparent reason? This
may be why if you are.

Flush out the bilge with fresh water after midnight when the greenies
aren't watching to get the little coolant out of the bilge...(c;

No fun....



--
Stephen

-------

For any proposition there is always some sufficiently narrow
interpretation of its terms, such that it turns out true, and
some sufficiently wide interpretation such that it turns out
false...concept stretching will refute *any* statement, and will
leave no true statement whatsoever.
-- Imre Lakatos

Stephen Trapani wrote in
:

It's raw water.



Sorry............................Yecch.

--
Larry

Larry wrote:

Stephen Trapani wrote in
:


It's raw water.




Sorry............................Yecch.


Any water passage I've seen in the engine still looks completely uncorroded.

Stephen

Try this:

Get a plastic milk jug, cut it open so you can wipe it clean with a
rag. Put fuel in it. Get some clear tubing from Lowes or Home Depot.
Run the tubing to the fuel fitting on the inlet to your fuel pump.
Fill the tubing with fuel and allow it to siphon the fuel from the milk
jug. Start your engine. If it does not lose power as it did before,
then suspect your fuel filtration.
The Yanmar mechanical fuel pumps seem to go bad all the time. I got an
electrical pump from JC Whitney that I put in series with the
mechanical one. It is wired to the starter so it always provides low
pressure to the engine. It keeps the engine primed.
It sounds like you have both engine timing and fuel problems. Valve
timing is easy to set on this engine. Injection timing is a little
harder but a COMPETENT mechanic can do it. You can do it yourself if
you can follow the directions in the service manual.

For cold starting, use the decompression levers. Relieve compression
on one or both cylinders, get it turning then put in compression, this
will get things lubed well and moving before you are trying to work
against the compression.

You might also check your fuel return line. If it is blocked, you can
have problems. When you are priming the engine, remove it from the
fitting on the injectors, blow into it (a little diesel fuel in your
moth will not hurt you) to see if it is clear.

Take the exhaust hose off the exhaust manifold and run the exhaust into
a 5 gal bucket This will fill your cabin with smoke so be careful but
the idea is to see if your muffler is clogged..

You really need to get a service manual. Try Mastry Marine in St.
Petersburg, FL for it.