Can water in cylinder milkshake oil?

Basic question is can enough water in a cylinder get into the engine oil to create a milkshake?

I have a boat with a 69 Ford 302 engine. For those who don’t know, the exhaust manifolds on inboards are water cooled. With age and overheating sometimes the water jackets in the exhaust crack allowing water to get into the cylinders.

My engine overheated from the loss of a freeze plug. I checked my oil and it is a milkshake. There was water in the number 4 cylinder and after pulling and testing my exhaust manifold I found out it was indeed leaking.

So, can enough water get past the cylinder to turn the oil into a milkshake? Or am I looking at two problems?




“Yes” and “probably”.
Yes on the account that water cannot be compressed and will push past the piston rings into the crankcase resulting in the milkshake. Overheating likely caused head gasket failure allowing coolant water to leak into the crankcase. I’d plan on pulling the engine - drop the oil pan for a full de-watering - bearing & journal check because even a small amount of water can wipe out the bearings in no time - and last but not least, pressure test the coolant side but I’d plan on needing head gaskets too … my honest opinin, from the issues at hand, I’d just rip it down completely, once you’re that far it ain’t nuttin to go ahead and pull the pistons out because once you have the oil pan & heads off, it’s not a big deal if you need to hone the cylinders, replace the rings and lap the valves since they’re right out in the open already.

Been a while since I did a marine engine but someone used to sell nickel-stainless header style manifolds, they handle the heat a lot better and are highly resistant to cracking but you must use the special gaskets, socket head capscrews and belleville spring washers to obtain & maintain a proper seal & performance. They ain’t cheap but cheaper than major repairs from water damage.

Ditto, and if the engine has been run very long with oil in this condition odds are the crankshaft bearings and possibly the crank journals are damaged.

Coolant diluted oil is a very poor lubricant and can do an engine in quickly.

I think the overheating has caused a failure of the head gasket. Do a compression check to verify the problem.

Thanks guys! Lot’s of good info here.

The engine only ran for a short time after the overheating, just enough to get back to the ramp. Seemed like forever but probably only 30 seconds. As it was running, water was still pumping through the engine, just not the manifolds. I cold see the temp gauge lowering. Of course the whole time I’m dumping water into the boat. I would have stopped completely but when I saw the water filled in the bilge I thought we were sinking.

Anyway, once I got home I checked the dip stick and noticed the milky oil. Checked the compression and it was good. Changed the oil, thinking maybe water worked it’s way in through the oil pan being flooded and all. I have a small leak so I thought this might be possible. Ran the engine with the clean oil for 10-15 minutes and she ran really good. But sure enough, started to see the milkshake return. I was stopping it every now and then to check the oil and the last time I went to restart I heard some knocking. So I pulled the #4 plug and sure enough water shot out.

That’s when I started looking at the exhaust manifold. So my plan is to hopefully have someone weld the crack if it is reachable. I still have not gotten the riser off of he manifold and will probably have to take it to a machine shop. These are rare Holman Moody manifolds so I’m hoping to not have to replace.

One that’s fixed up I will change the oil again and see if it fixes it. If not, I’ll pull the intake and heads. Hoping to not do a rebuild at this point unless necessary.

We have a great forum for these boats but lots of people were unsure if enough water could get past the cylinders to milkshake the oil.

Thanks again for your help and any other comments you all may have.

Something doesn’t add up. If you had that much water in a cylinder the engine should be hydro-locked.

It would take alot of water leaking past the rings to turn the oil into a milkshke color. If there was that much water in a cylinder the engine shouldn’t even turn over.

If you have enough “blowby” because of worn piston rings, your oil will be a milkshake because of the water in the combustion gasses mixing with the oil. For every gallon of fuel burned you get a gallon of water as waste product.

Define what you mean by good compression. People post on here all of time about having good compression readings and when the actual readings are given those figures often show a problem.

Water in a cylinder won’t necessarily cause hydrolock if the head gasket is gone.

“Define what you mean by good compression.”

The lowest reading is within 75% of the highest.
Highest is 130, lowest is 110.

I am on Team Willey with this one and saying fixing your exhaust manifold will not stop your engine from making milkshakes, the water is getting into the oil in another way (the engine overheated from the loss of coolant and continued operation not from the loss off a freeze plug)

Team Willey sounds fun! The engine may have the feature of sucking exhaust gas back into the fuel delivery system to be re burnt and picking up a lot of moisture to add to the system. I would not think that would foam the oil, but who knows. (Still thinking head gasket) worn rings would not give those I believe acceptable numbers for compression. A new pcv valve at this time would not hurt either.

Well, to be blunt those readings suck. Even the 130 is horrible.