The Stovebolt Site Forums The Shop Area Engine Shop Antifreeze in my oil

Bought a GMC 55 first series P/U with a 248 ci engine. Previous owner ( also a good honest friend) said motor was rebuilt 200 miles ago by local reputable shop. It sat in his drive way for 3 years with antifreeze in it.

I dry started it last week, 30 seconds,to insure all was ok before putting freshly painted fenders on. It started easy and sounded great. I drained the oil for an oil change, and noticed green antifreeze was 1/4 of the drain pan contents with milky grayish oil floating on top.
Where do I start looking , testing, and doing?

Only thing I can think of is head gasket was installed improperly or the wrong gasket.if it was rebuilt was the head checked for cracks? The good thing is antifreeze will sit on the bottom of the pan if it was sitting the crank and bearings should be good if it was not run for any length of time.Maybee check to see if the head bolts are torqued properly.

"Milky grayish oil"- - - - -definitely not a good sign. I'd suggest draining as much oil as possible, drain all the coolant to prevent further contamination, and refill the crankcase with 4 quarts of inexpensive oil and a gallon of Diesel fuel. Run the engine for a minute or less, 3 or 4 times, to flush as much contaminated oil as possible out of the rods, main bearings, valve train, etc. Don't let it get too hot.

Then pull the cylinder head and look for a damaged gasket or other evidence of incorrect assembly. It might also be a good idea to get the head pressure tested by a machine shop to look for cracks, if nothing obvious is found wrong with the head gasket. Good luck!
Jerry

I would try to get as much info on the leaks before tearing it down.

Could fill the cooling system with water. No oil leave the drain plug out.

Put 10-15 psi in the cooling system and see if holds pressure, observe the cooling system for leaks into the oil pan of any of cylinders. Not a sure thing test because some leaks or cracks or head gaskets can leak only when hot.

Head gasket is the logical first cause, but cracks in the block and or head is a runs strong second.

Thanks for the advice, I will check it out and flush the bearing surface like it was suggested. I did not expect this issue but I'm trying to see it as just a bump in the road.

I left the drain plug out and filled the cooling system with water. I borrowed a pressure tester and tried to pump it up but it would not hold pressure. It would go to 4 pounds and quickly go to zero between hand pumps. It did start to flush old milky oil into the catch pan. I guess pulling the head is the next step.

If there was antifreeze in the coolant, be aware that it's all through the lubricating system, and will remain there to contaminate the next filling of oil even after you find and fix the source of the intermix. That's why I suggested doing a flush of the lube system before tearing the engine down to the point it can't be run. Getting antifreeze contamination out needs to be done sooner, rather than later.
Jerry

Good point, I will flush the lube system before I pull the head thanks

After I did a temporary fix with water glass on the head gasket leak on the 500-something cubic inch GMC Ed Pruss had problems with on his way to Denver, there was coolant in the oil. I did an oil change, removed the filter cartridge, and added a gallon of Mineral spirits to the crankcase. It did a very good job of removing the milky contamination after running the mixture for 30 minutes or so at a fast idle. Just don't drive the vehicle, or put any other load on the bearings. Diluted oil isn't a good lubricant!
Jerry