Gas in Oil (Atomic 4)

[jeanathon]

Help me trouble shoot this specifically for the Atomic 4. The clues.
I went to help a friend move his boat from a boatyard.

1. It had been moved to another slip.
2. Key was in the on position.
3. There were some new oil soak up pads on the galley counter, and a soiled one in the bilge. (which caused us to check the oil.)
4. The oil on the dipstick was very thin, black, and within the high low marks. (which caused us to pump out the old oil and replace.
5. The oil we pumped out had the viscosity of water and was black. (no milk. It seemed to be mostly gasoline although I did not ignite it to confirm that.)
6. After refilling the engine with oil it started pissing out of the back of the transmission at the shaft, and was still not straight oil.
What happened? I have some thoughts, but want to see what you all come up with. Atomic 4 experience preferred.

[rslifkin]

Is it an electric or mechanical fuel pump? If it's electric and runs at key on with no oil pressure interlock it may have overwhelmed the carb float and needle valve. That would have flooded any cylinder with an open intake valve with gas, allowing it to seep past the rings into the oil. You'd probably smell fuel from the carb with the carb, intake manifold, etc. being full of fuel. And depending on how fast it leaked down, the engine could possibly be hydrolocked. This failure could happen while sitting with the key left on if the pump pressure is too high or the carb float/needle isn't sealing well.

If it's a mechanical pump, they can leak into the crankcase on many engine designs (not 100% sure on the A4) and dilute the oil. This would have happened while running, not while sitting.

[jeanathon]

One clue I left out is that it was at the boatyard for carb work, and I believe got a new carb.

[jt11791]

Originally Posted by rslifkin

Is it an electric or mechanical fuel pump? If it's electric and runs at key on with no oil pressure interlock it may have overwhelmed the carb float and needle valve. That would have flooded any cylinder with an open intake valve with gas, allowing it to seep past the rings into the oil. You'd probably smell fuel from the carb with the carb, intake manifold, etc. being full of fuel. And depending on how fast it leaked down, the engine could possibly be hydrolocked. This failure could happen while sitting with the key left on if the pump pressure is too high or the carb float/needle isn't sealing well.

If it's a mechanical pump, they can leak into the crankcase on many engine designs (not 100% sure on the A4) and dilute the oil. This would have happened while running, not while sitting.

A stuck carb float won't do this on an A4, the gas will run out of the air intake, not into the cylinders.



A failed diaphragm in a mechanical fuel pump will dump gasoline into the oil pan, so that is a strong possibility.



It sounds like there is also a bad oil seal on the output shaft, but possibly the leak will stop when there is normal viscosity oil in the motor.

[capn ken]

Try the atomic 4 web forum . The afourians . Does the engine turn over by hand ? Pull the spark plugs and repeat .compression ? A rag or thumb over the hole while cranking willgive you a good idea of the internals . I’ve never heard of an a-4 “pissing” out the tail shaft unless the oil is way overfilled . How many quarts of oil added ? If fumes are present ventilate the boat ,turn on the bilge blower. And then and only then attempt a restart ,whilst eyeballing the transmission tail shaft ! The web forum at the aforiand may have other ideas . You can also get a complete manual for under 20 bucks from Moyer marine .don Moyer is the Man ! Good luck and think positive .

[Ballsnall]

Highly likely it's a busted fuel pump diaphragm. Only other reasonably likely scenario is someone topped the oil up with fuel.

[gonesail]

ruptured fuel pump diaphragm definitely worth checking out

[Stu Jackson]

Wait, nobody's mentioned moyer yet?

[sinnerman]

Originally Posted by Stu Jackson

Wait, nobody's mentioned moyer yet?

Exactly as Stu suggested.
https://moyermarine.com

My two cents are also on a failed mechanical pump diaphragm.

cheers.

[Boatyarddog]

Originally Posted by rslifkin

Is it an electric or mechanical fuel pump? If it's electric and runs at key on with no oil pressure interlock it may have overwhelmed the carb float and needle valve. That would have flooded any cylinder with an open intake valve with gas, allowing it to seep past the rings into the oil. You'd probably smell fuel from the carb with the carb, intake manifold, etc. being full of fuel. And depending on how fast it leaked down, the engine could possibly be hydrolocked. This failure could happen while sitting with the key left on if the pump pressure is too high or the carb float/needle isn't sealing well.

If it's a mechanical pump, they can leak into the crankcase on many engine designs (not 100% sure on the A4) and dilute the oil. This would have happened while running, not while sitting.

One one problem with this diagnosis.
Atomic 4 uses an updraft carburetor, usually a Palmer.

In any case fuel that is not stopped by a stuck or hard rubber needle, would exit thru the throat.

It may have an mechanical pump, but the ones I've seen have electric pumps.
More info is required.

Oil is shared by the drive unit in a common oil pan.
Gasoline laden fuel may have comprised your drive units rear seal.
Change it out.
And the fuel pump if it's mechanical.

Otherwise, drain all oil refill and recheck.
Boatyarddog

[Boatyarddog]

Originally Posted by Ballsnall

Highly likely it's a busted fuel pump diaphragm. Only other reasonably likely scenario is someone topped the oil up with fuel.

If it's a mechanical pump, why is it highly unlikely?
Happens often with older engines.
Also, highly unlikely some topped the engine oil off with gasoline, as the poster says the oil was between the high and low mark.
Boatyarddog

[Boatyarddog]

Originally Posted by jeanathon

One clue I left out is that it was at the boatyard for carb work, and I believe got a new carb.

Depending on why you got a carb or repair, these are updraft carbs, excess fuel comes out the carb throat, and cannot fill up enough to get into a cylinder.
Boatyarddog

[captlloyd]

It was stated that the carb can’t leak into the engine, that may be true but I would still turn it over with the plugs out to be safe.

[jeanathon]

Thanks all.

[jt11791]

Originally Posted by Stu Jackson

Wait, nobody's mentioned moyer yet?

Post #5