The Stovebolt Site Forums The Shop Area Engine Shop 1947 GMC 228 with oil in radiator?

Hey all,
47 GMC with 228.
Last year I was driving and had the engine boil over (water coming out of radiator cap).
Last fall and not as I'm looking into some things, I noticed some oil collecting at the top of the radiator.
Not a whole lot but definitely oil. You can soak it up with a rag and it will come back.
I checked the pan and does not appear to be any water in the oil - which is good.
Thinking I may have a head gasket blown or hopefully not a cracked head or block?
Checked the cylinder pressure and they were all between 90 and 110. only two cyl's at 90/95 other 4 at 100/110.
This pressure seems to be about the same as what I had before the issue.
I was thinking if I had a blown head gasket that the pressure loss might be noticed more on one of the cylinders.

Any other ideas or thoughts?

Thanks,

A blown head gasket is the most likely culprit unless there's a crack in the water jacket somewhere.

It's a zero pressure cooling system but the crankcase oil pressure is 7-15psi so oil is more likely to flow into the cooling sytem through a small gap rather than the other way around.

Oil pressure on his GMC engine will be a lot higher than that. My 228 is 45-50 PSI when warm at highway speeds using 15w40. Maintenance Manual calls for a rebuild when that drops below 25 psi.

OK. I was thinking of a 216.

The point, however is that the fluid will move from the pressurized side of the leak to the low / no pressure side of the leak. Thus oil will be found in the coolant and coolant might not be found in the oil.

Do a cylinder leakdown test instead of a compression check. With both valves closed on each cylinder, apply 60-70 PSI to the cylinder through the spark plug hole, and lock the crankshaft by putting the transmission into high gear and setting the parking brake and/or chocking the wheels. If a pressure leak is present, you should see bubbles in the radiator. A leak from an oil passage to the cooling system won't show up that way, however.
Jerry

It is very unusual for a GMC to have oil in the water. You really don't have any oil galleys near the water jacket. I rebuilt my first 228 over 65 years ago, and I can't ever remember getting oil in the water. Water in the oil was very common. Heads crack, warp allowing head gaskets to fail an cylinders crack. All of this will put coolant in the oil. I would check under the rocker cover. If you have some white slimy stuff you are leaking coolant into the oil and you need to find the cause. If there is no slime under the rocker cover, I would just run it. It might not be a bad idea to put a can of stop leak in the radiator and see what happens.

I would explicitly *not* put a can of stopleak in the radiator. That will gum up the whole cooling system and make it much harder to fix right later.

This is an almost 80 year old machine. I have been putting stop leak in them for around 70 years and I have never seen stuff get gummed up or be harder to fix later. I run a fleet of trucks with Cummins engines. We use K-Seal in them for about 20 years. We rebuild the engines in house and have never found any kind of residue.

Stop leak products that contain metallic powder such as "Silver seal" can and do clog up radiators. I once pulled a radiator from an old Ford van that must have weighed 15 pounds more than the replacement one we installed. We pulled the bottom tank and found it was completely full of aluminum powder. Vegetable fiber sealers like Bar's Leaks don't clog things up under most circumstances, but anything can be over-used.
Jerry

no water in the oil or under the valve cover.
It doesn't looks to have been much of an issue - maybe a one time deal if it overheated?

Welp,
I drained the radiator with minimal oil in there.
As noted in a reply above, maybe it was a one time event during an overheat scenario.
But, I have pulled the head and am replacing the gaskets as well as grinding the valves as long as I'm there.
It does look like there was some leakage from the cylinders - that could be seen on the head/gasket areal.
getting some good spring cleanup done on the motor if nothing else!
Thanks for the replies.
I'll try to update you after I get it back together.