I've got around 36,000 trouble-free miles on my current engine. (345 hp Ford Performance 302 crate engine.) In late June on our annual Utah Cobra Club cruise my car started puking coolant from the recovery tank. It's a typical setup; a capless radiator only having an inlet and outlet with a separate coolant recovery tank. (I'm running a Mustang radiator that has brazed cap closing the stock radiator cap fitting. It's got an aluminum CSR in-line radiator filler located on the upper radiator hose.) The overflow line runs from the CSR fitting to the bottom of the coolant recovery tank.

The ambient temperature was over 100 when the first episode occurred while in Colorado. Although the recovery tank kept overflowing during our cruise when I stopped the engine, it was an intermittent occurrence. The engine never overheated during the 1400 mile trip. When I got home I tested the 13 psi rated radiator cap and found that it relieved pressure at around 8 psi. So I replaced the cap thinking that was my problem.

Well, on Saturday we went for a day trip of almost 300 miles. Once again my engine performed perfectly with no overheating. However, as soon as I pulled into the garage and turned the engine off I immediately heard coolant transfer. Sure enough, coolant had transferred into the coolant recovery tank. I realize that in itself is not a problem and how it's supposed to work. However, once my engine cooled-down it did not recover any coolant from the recovery tank.

Any thoughts on my issue? Head gasket, leak, air pocket?

I really want to determine the cause of my problem before I start changing head gaskets.

Thanks.