Water in Engine Oil

I have an 86 bayliner with a 350 chevy and a volvo penta outdrive. I bought the boat in July of last season and the guy I bought it off of ran without a thermostat. I put one in this season and now I have milky oil. I changed the intake gasket and the exhaust gasket and still have milky oil. I took the thermostat out and started with fresh oil and now the oil is clean. I've had several people say it could be the head gasket or the head in general. I was wondering if anyone has run into this problem before? THANKS

 

I have not.

However, running without a thermostat is not a good idea at all.

Have a qualified mechanic check it out. He/she will likely do a pressure test.

My money is on either an internal crack or a faulty head gasket.

Good luck, Tom

 

Submarine Tom is probably right, but I was once getting water in the oil in a Volvo Penta 3 cylinder diesel. We stripped it right down and could see water had been at the lower rear cylinder so assumed that was it and fitted new gaskets and rebuilt everything.
After running the engine the water started appearing again. I suspected the mechanically driven water pump although there was no water coming from the tell-tale hole between the shaft's oil and water seals. I fitted a new shaft and seals and never saw water again.
When the boat was out of the water, I sometimes ran the engine with a hosed water supply. I can only assume that I had pushed the water seal out enough until it came against the oil seal and the water found a channel along the worn shaft into the engine once it had been shut down and the sea cock was still open.

In your case, you know that you get leaking only with the thermostat in place, so it is likely heat related, but don't discount that it might be a difference in pressure build-up caused by blockages (increased resistance to the water flow).

 

had this problem with a ford 351, ended up being a roten intake manifold where the water gallery is intering the block, other way to find is to run strong solution of dye thru water and unfortunetel strip engine down and see where the dye is entering, sometimes the easy way is the hard way in the end, could be something simple but they have a relatively thing bore lining especially after being rebored in its life as sometimes i have seen some dodgy alihgment of the cylinder bore when reboring.

 

Water in the oil is a bad sign. Repairs to the leak can be made but once water has run with oil in the engine, internal engine damage has occurred. You will need to rebuild the engine or risk premature failure, unfortunately.

 

If the water pump is leaking on the valve cover it will corrode and get water in the oil. It is one of the places for water ingress

 

Good thinking Gonzo, but shouldn't that be the timing chain cover?

 

Yes, they are sheet metal and was quite thin on the old ones. It gets small holes on the top under the water pump.

 

If it had the marine water pump the back plate would be stainless
Is it a Volvo marinised engine or a DIY engine?

 

If it has an oilcooler it might be leaking.

Dino