[lust4speed]

Originally Posted by Schurkey

Any coolant that bypasses from the back of the engine direct to above the thermostat is coolant that's not picking up heat from the cylinder head....

Exactly. Pulling coolant away from engine when it has only completed half its cooling journey.

[Schurkey]

Originally Posted by lust4speed

Exactly. Pulling coolant away from engine when it has only completed half its cooling journey.

Realistically, NOT EVEN half.

That coolant has been through the block--but the heads have more BTUs than the block does. The critical part is the cylinder head, and that's what's being cheated of coolant volume.

The heads having more BTUs than the block is why Pontiac originally cooled the heads first, then the block using the "Gusher" cooling system. This was abandoned in '59 or '60, I can never keep that straight.

Chevy did exactly the same thing with the "LT1" engines of the early--mid '90s. Made a big deal about cooling the heads first, then the block. And again, GM Powertrain abandoned it for the LS engine.

Even International played games with cooling the cylinder heads first, then using that coolant to go through the block on the SV engine family.

Certain Harley V2, and Porsche engines water-cool the cylinder heads, but air-cool the cylinder barrels.