Has anyone ever used a liquid to liquid cooler on a home built. I know
this type of cooler is normal on a turbin engine but what would it do to
a normally asperated engine and none JP rated fuels?

What do you have in mind, using a heat exchanger to cool your oil and warm
up the avgas in your tanks?

It shouldn't take long, a few minutes, to vaporlock your engine that way.
:-(

Or, what did you have in mind?

Paul