Exhaust gasses in radiator

35th T-bird SC

Registered User
I/m trying to narrow down where I'm getting exhaust gasses in my coolant after this rebuild I did. When I leave the cap off the radiator and start it it starts to bubble. I also get bubbles in my overflow when the motor is warm. I did a cooling system pressure test and it dropped about 1 PSI after two minutes. So those are my reasons for thonking the worst. Today I did a compression test with the car on ramps. I got 150 PSI on all the cylinders. At least the rings are sealing and that part of the rebuild went fine. So how do I narrow it down to at least which head? Maybe I have a cracked head because the head gaskets are new?
 
Let's assume that nothing's cracked.

Coolant can get into the cylinders from either the intake manifold gaskets or head gaskets.

But, you have air getting into the coolant, which can happen if...

- intake gasket is bad and the supercharger is presurizing the intake allowing air to get from the intake track to the water jacket.

- or you have a blown head gasket.

A blown head gasket can often pass a compression test, because, if the leak is small, it will leak only when the fuel ignites (high pressure). You can't produce enough pressure with a compression tester - unless it's a big leak.

If you can find nothing else besides what I mentioned above causing the problem, then you have to take off the intake before taking off the heads, and you will see right there if the intake manifold gasket is the culprit.

If you have a compressor, you can pick up a leakdown tester and do a leakdown test. This will tell you if the cylinder's leaking, and, if so, where from. It still may not be enough to cause the head gasket to leak in some cases.

About which head might be leaking, you can take out one plug at a time and start it up. When the bubbles stop, that will be the cylinder that is leaking. You can try just taking off the spark plug leads one by one, but you may end up fouling a plug or two. I'd take the chance and just take off the spark plug wires and see if that tells you - because I'm a lazy bum and would do what's easiest!

I hope that helped.
 
Good points, that makes me think back. I had the heads milled and the block decked, would that be enough of metal taken off to allow the intake manifold to no match up with everything to leak? I put permatex #2 around the coolant holes of the intake manifold (each corner).
 
I known that milling and decking can sometimes create a problem with intakes not matching up. I guess it depends on how much was milled.

I was on another site recently, and that's exactly what happpened to some other guy (on an old cast iron big block Chevy) - and it was his intake that was leaking because it didnt match up that well, with bubbles in the water and all. He was getting water in the cylinders, as well, and he was leaking from all the water joints on the intake gaskets.

Maybe some other guys have dealt with this, or there's an aftermarket gasket that is thicker.

Good luck.
 
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