I have a 2004 Honda Civic that's driving me to drinking.

It pushes coolant out of the radiator and into the overflow tank, even to the point of overflowing the overflow tank. It seems to do this even when it's not very hot, so temperature, although related, does not seem to be the main issue.

We started by doing the easy stuff - thermostat (3 different ones by now!), radiator cap, pressure test the head and head gasket. No luck.

Then took it to a Honda dealer, who did an "acid test" of the gases coming out of the radiator and said it showed signs of combustion gases bubbling out. So we had the head shaved and a new head gasket. But its still doing the same thing.

There's no sign of coolant leakage, other than the overflow from the overflow tank.

Please help. My wallet is nearing empty!
Dewby

Possibly, corrosion or mineral buildup is restricting the passage ways in the radiator. It may need to be rodded or replaced. This would be very unusual on such a new Civic. Remember to only use distilled water with your antifreeze.

I agree with Tex. You have a flow problem. And when things don't flow freely, it takes the path of least resistance. It your case either a weak radiator cap, or a backing up radiator core. You have done what I would have guessed, and I don't think the mechanic's made any wrong decisions. Next have that radiator checked by a shop that specializes in just that.