[waterrat2]

I have an old Volvo Penta MD 7A. At the end of last season I noticed that the oil level seemed to be increasing above the “full” mark. There is no sign of water in the oil, but it seems to be thinner than it should be, so I think it must be diesel somehow getting into the oil. I changed the oil (filling to the proper level) and it seemed OK for a few weeks of regular starts – one time running for about four hours. But when I was laying the boat up for winter I cranked the motor for a long time (with the decompression lever open) to get anti-freeze in the water jacket. Unfortunately I didn't think to close the fuel valve and when I checked the oil level, afterwards, it was again very high. That makes me suspect the diesel is pushed through somewhere only while cranking and not while running.

Does anyone have any ideas what I should look at? (No, I can't afford a new motor.)

 

[JimsCAL]

First place I would look is the low pressure fuel pump. If mechanical (not electric) a bad diaphragm could allow fuel to leak into the crankcase.

 

[newhaul]

With all the indicators you describe I would actually suspect fuel bypassing the rings when not running about how many hours on he engine and is it an easy start or take some cranking to et fire?

 

[MedSailor]

If it's only when cranking but not when running consider that it is being injected into the cylinders and not combusting whereby it leaks down past the rings into the oil pan.

An oil analysis is cheap and would be useful to prove it is diesel before you go barking up the wrong tree.

A leak-down test would be useful to prove that the rings are leaky leading to this issue.

Med

 

[waterrat2]

Thanks for all the reply's and suggestions.

newhaul, It's an old motor, about 1984, but I don't have any idea how many hours there are on it. It starts pretty easy. Most of the time takes 4 to 6 seconds of Cranking even cold. By cold I mean first time in the day. I seldom start it when the temperature is under 50 deg. F. When the motor is warm it starts even faster.

It will probably take a while before I get to try anything. The weather won't be good this week for getting under the tarp. I'll post again when I find out anything.

 

[newhaul]

Thanks for all the reply's and suggestions.

newhaul, It's an old motor, about 1984, but I don't have any idea how many hours there are on it. It starts pretty easy. Most of the time takes 4 to 6 seconds of Cranking even cold. By cold I mean first time in the day. I seldom start it when the temperature is under 50 deg. F. When the motor is warm it starts even faster.

It will probably take a while before I get to try anything. The weather won't be good this week for getting under the tarp. I'll post again when I find out anything.

With that information I am leaning hard towards leak down past rings do an oil analysis as med suggested to confirm and if it is just happening when cranking with compression released just remember to shut off fuel before maintance for decommissioning for winter

 

[Rockter]

Check the diaphragm on the engine-mounted lift pump. It may be leaking. That's all I can think of.

I don't think that leaking past the rings would do it. they would have to be leaking like crazy for that and the compression would be very poor.

 

[waterrat2]

I'll try that. I hope I can find it, and that it's not on the back end of the motor. Except for the front, the motor isn't especially accessible.

 

[hpeer]

The fuel lift pump is in the back Port side of the motor. About level with the top. It is round.

It has a small lever underneath it. Reaching in from the front if you lay your hand over the pump, and curl your fingers around underneath it will be about your middle finger. This lever operates the pump.

It is driven by the engine. But you can operate it manually. It has a spring return. But if the spring is busted you can still use it, you just have to drive it up and down manually.

 

[Capt Len]

My guess is the fuel pump diaphragm. Much of the leaked fuel will evaporate when the engine is hot but piles up when cold. At some point many engines will decide to run full tilt /disintergrate (pathfinder,engish ford to name a couple). A switch to electric pump (and a spare) will also assist in bleeding and filter changes

 

[Cal31Windchaser]

I just found this thread and apologize for posting so long afterwards, but a very timely subject for me. I have a Universal 5416 with electric fuel pump. Was doing a lot of motoring down the Tennessee and Tenn-Tom Waterway. Observed oil level rising. Stopped at Marine Maintenance in Pensacola to have it checked out. They said in my case the number one suspect was the injectors. They said injector timing could be off and fuel was washing down the cylinder walls.

Replaced the injectors (Kubota not Universal, which is another great story on how to save money). Engine starts much, much easier and oil rise seems to have abated, although we only motored from Pensacola to Carrabelle where she sits right now.

Anyone else have a similar experience?