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I inherited my Corvette from my dad, it's a big block and many years ago he added an expansion tank. He said it never had one. Are there benefits to having it or should I ditch it?
So you shouldn't have two functioning pressure caps. The expansion tank needs one but it was designed for a radiator that has no cap. For your system to function correctly you need the radiator to use what is called a blank cap. There is no spring pressure mechanism under the cap just a full rubber seal to prevent leakage. This way the normal air chamber on the top of the radiator is filled with coolant and the only air pocket is in the expansion tank. I found a number of British cars use blank caps or just try Google for blank radiator cap.
Expansion tank
