My 1973 Impala (400 small block, if that makes any difference) sat for several months. I ran a battery down today trying to start it. I went to autozone to find something to help me start it. The guy told me to pull out the spark plugs, spray WD-40 in the cylinders, then crank it a few times with the plugs out so there was no pressure.
Most of the plugs were either dry or oily. One, however, had water with coolant (antifreeze-colored water) pour out of its socket as I removed it. No, this car hasn’t been in a flood, nor has water been allowed down into the carburetor. I’ve read on here the answers to similar questions and, other than for those who had had water poured into their engine, the answers ranged from: huh?; you need a new manifold; and you might need a new gasket. The models referred to were much newer models so I do not feel safe assuming my problem is exactly the same. Furthermore, about 13-14 years ago I had an intake manifold gasket fail and its defining feature was the oil turning thick and goopy–paint-like. That hasn’t happened yet, but I also recall it took a while for the oil and coolant mixed to turn goopy (I was in New Mexico when my coolant started mysteriously disappearing, but I was back to Oklahoma before the oil got goopy.).
So I guess my question most of all is: how do I pinpoint the cause of my problem?
Intake gasket has failed OR a head gasket as failed. Both can be issues on 400 Chevy. Since the manifold was a problem years ago, I’d guess that is the problem now.
If you position that cylinder to top dead center where both valves are closed, and then apply compressed air to that cylinder, and then see bubbles in the coolant in the radiator, that’s a blown head gasket.
The heads need to come off for a close inspection of the situation. But the area between cylinders pairs 3-5 and 4-6 are notorious for heat failures on small block 400 engines.
Small block Chevrolet 400 engines have weak gaskets between the cylinders and the 2 pairs that I mentioned are especially weak. When the gasket fails with a narrow gap in the gasket between cylinders continuing to run the engine can throw a cutting flame through the gap and melt away metal from the block and head and the damage cannot be repaired.
Concur with the manifold or head gasket guess. A shop can do a test called a “leak down test” for that particular cylinder. If it is just one cylinder involved, should be at a fairly reasonable cost. The results will provide a pretty good idea what the problem is. With any luck it is just an intake manifold gasket problem. I have a Ford truck from that era so I’m well aware of the sorts of problems we owners of vintage vehicles run into. I had to do a diagnoses & repair in a hardware store parking lot a couple months ago. Part of the fun and challenge of owning a vintage vehicle.
The reason tester replied what he did is because if is intake manifold gasket failure, the way the coolant gets into the combustion chamber is when the intake valve opens. If you rotate the engine so the valves are closed on that cylinder, coolant can’t travel out of that cylinder into the intake manifold so it will be forced to leave via a bad head gasket or cracked head or block.
If the problem is a manifold leak, the valves will seal the air and the only leak will be a small amount past the rings into the crank case.
That’s a good idea @texases. Boring a 400 small block to rebuild it worsens the likelihood of a failed gasket while a proper 350 engine is nearly bullet proof.