Milky Oil

Can you pull each plug and see what’s up in each cylinder? Might be a leaking head gasket from the overheat (warped head possible too). If it’s one cylinder—might tell you where the water is getting in. Manifold gaskets are a possibility too. I’ll let the experts weigh in. All of my recip engine education was air-cooled Lycoming and Continental engines with an occasional Wright thrown in. In other words, wait for better advice sure to follow.

The sudden loss of power. Can you describe it in detail? Was there ever black smoke from the exhaust at the overheat or afterwards? Could be a collapsed exhaust hose along with a blown gasket (head/exhaust/intake.

Also: when you changed the thermostat: did you make sure to get a good seal on the new gasket? I’m not sure if there’s any chance the thermo replacement could mess things up, but is was the last thing you did.

The thermostat was put in by me he day before. I just bought this boat and discovered it did not have one installed. The boat ran cool but I thought it should have it in there. After it over heated I took it back out and ran it the way they did without one. I was just trying to do the right thing and wish I would have left it alone.

Andrew,
Did you by chance check the oil before or immediately after you bought the boat? Wondering if you purchased a previous problem.

You did the right thing with putting the T stat in. The engine is designed to run with one.

Do check for collapsed exhaust hose. With engine overheats, there are times where the inner layer of hose disbands to the outer and then folds in restricting the exhaust.

Yes the oil look nice and clean. So with the compression test good that rules out head gasket or warped heads correct?

Wait I may of thought of something. That evening before we pulled the boat out I had to run the bilge pump a long time. Water was up to the floor almost. Could it have drained through the oil dip stick tube?

Evilsizer wrote: Wait I may of thought of something. That evening before we pulled the boat out I had to run the bilge pump a long time. Water was up to the floor almost. Could it have drained through the oil dip stick tube?

The water would need to be higher to get into the oil.

Where did the water come from?

Also what is the correct thermostat for this old 78 351 commander? I m sure I put it in correctly. Someone stated that without a thermostat and running at idle for a long period of time in cold water can cause water in the oil. Below is what they described. we were running at idle in no wake zones for a while in cold water but am not sure how that will allow water in engine
1. Water in boat bilge
Boat has been submerged or bilge water was
high enough to run in through dipstick tube

2. Water seeping past piston ring or valves
Refer to "Water in Engine" ("On Top of Pistons")

3. Engine running cold
Defective thermostat, missing thermostat;
prolonged idling in cold water

4. Intake manifold leaking near a water passage
Loose or cracked intake
Bad intake gasket
Corroded head or intake

5. Cracked or porous casting
Check cylinder head, cylinder block, cylinder walls,
and intake manifold

6. Valve cover cap or breather missing, ( only gets water when it rains)

The only way to know is the fix the problem and find out what you have after the repair.
Hard to say where the water came from we would only be guessing.
You need to check it out and learn what you can.
The biggest danger from taking on water would be HYDROLOCK.   If water is on top of a piston and you hit your start key it can bang the piston against the water compressing the water against the cylinder head. This can bend a connecting rod and then you are in to a full rebuild.   If you hit the starter and your engine spins but then locks pull the spark plugs and let the water out before ever hitting the start key again.
The exhaust tubes are pretty strong and not easy to pull off. Warm the exhaust hose up at the connection with a Hair dryer,   Warm hoses are much easier to work with. Have a squirt bottle with strong soapy water. Slip a small flat blade between the exhaust manifold outlet and the exhaust hose and run soapy water inside. Work your flat blade around and keep adding soapy water inside.
Pull it off the exhaust manifold.   If it is collapsed it will be collapsed very close to the exhaust manifold where the heat is the hottest. When you look inside you will see the tube collapsed and burned rubber.
They stink when this happens you can smell that the tube gets hot when the engine overheats.

Evilsizer wrote: Wish I knew how to post pics on here. .

Andrew,
Click on the full reply icon above. It's the arrow pointing northeast. Then click the image upload icon. It's the tree with the up arrow. Then a browse box will come up allowing you to select anything off your computer. Mobile devices don't work very well with the site.

Your marine conversion looks differant than my 78, mine was a PCM yours looks to be a Commander, they both work fine' I am just wondering why Nautique would use two sources for engines in the same model year. Good Luck finding the problem.
Nice Looking 78!

Ohio guy with the block M?

Go Blue

MrMcD wrote: yours looks to be a Commander, they both work fine' I am just wondering why Nautique would use two sources for engines in the same model year.

Mark,
Yes, it's a Commander. The 70's were pretty lean years for CC with lots of cash $$$ flow problems so they bought what engines they could. Go back a few years and it was standard to offer 4, 5 or even more brands of engines. Also many models had the OMC upgrade option.

Thanks guys. I have learned a bunch!! I hope it is just a hose collapsed!!

This may be rather silly of me, but there have been 29 posts in this thread with nobody asking how hot your engine got.

So i'll ask, how hot did it get?

Was it billowing steam out from the engine box/exhaust or did you just notice the temp gauge going up? Smell like hot rubber?

Your earlier threads dealt with a bad impeller and overheating at idle, how hot were these temperatures at the time?