1966Oldsmobile

What do I have to do when I have oil in my cooling water? Anything else but changing the cylinder head gaskets? Its a ´66 330 f85.

Thank you very much!

MDchanic

Could also, maybe, be an intake manifold gasket.

I'd check compression first, and go from there.

- Eric

1966Oldsmobile

I have no tool to check the compression. So I buy a new intake manifold gasket too! Maybe change/fix anything else?

Thanks for your quick answer

Oldsmaniac

Often the water pump backing plate rusts thru and allows water to mix with the oil. With this problem your oil will have coolant in it but no so much the cooling system laden with oil.

MDchanic

Might be cheaper to just drop twenty bucks on a compression gauge first, then decide what you want to change.

And, yeah, like Joe says, that flat steel plate behind the water pump always gets pitted, and if rotted through will probably pee water into the oil, and possibly some oil into the water.

- Eric

1966Oldsmobile

As a classic car newbie: what should the compression gauge show and how to interpret the result?

Thanks a lot

MDchanic

Well, I have no personal experience with 330s, but depending on whether your engine is high or low compression, I would expect somewhere in the 120 to 170 psi range.

The important thing is not the pressure, but the variation.
If all of your cylinders are between 155 and 165 psi, but two of them, right next to each other, are 70 psi, then you can bet that the head gasket is leaking between those two cylinders.

- Eric

m371961

Auto or manual transmission? Is there any water in the engine oil?
If auto, maybe trans oil from cooler tube in radiator.

oldcutlass

x2

1966Oldsmobile

Automatik transmission! No water in the oil system. Hmmm

m371961

Most likely trans cooler line in radiator. Can be tested if you are handy, or remove radiator and have a radiator shop test it. Or if you are not concerned with originality, remove lines and install a separate cooler, flush radiator and drive.
Most times oil in coolant has to come from a place where oil leaks under pressure that overcomes coolant pressure.

Oldlords

I second this. If there's transmission fluid in your radiator there's really only two ways it could have gotten in there. One, someone put it in there or your
transmission lines that run to your radiator for cooling are leaking inside your radiator and mixing with your antifreeze.