[srmmmm]

I've run a 180 thermostat with a 1/16" hole forever to allow some heated water on the backside of the thermostat which always seemed to reduce the engine temperature swings during extreme cold temperatures. Without it, it seemed the thermostat would "pop" open at temp, then I'd immediately lose 25-30 degrees as cold water from the radiator hit the engine. With the hole, the engine didn't reach operating temperature quite as fast, but the thermostat seemed to open smoother, avoiding the cold water shock.

[HWYSTR455]

Originally Posted by chuckies76ta

I see many confused about the direction of flow of the block holes. The water flows out the stat, or when the stat is closed, circulates in the block/heads/core/pump areas.

So, if the cross-over bypass is blocked and the heater hose return to water pump Timing cover is blocked, and a thermostat installed, there will be no circulation in the block before thermostat opens? So then you have potential for the water pump cavitation. Thank you. What are your thoughts?

Well, I said 'circulates', but believe it just kind of sits there until the stat opens.

If the stat has opened a couple times in use, there is no, or very little air in the block/heads/core. The pump will just spin like a prop on a ship, water just won't go anywhere, and it won't 'cavitate'. Without air, you can't have cavitation.

Technically, cavitation can only occur at the pump/pump housing.

If the 'bypass', which is actually a 'bleed', is blocked, it could potentially prevent air from dissipating via the stat>rad. Where that air gets trapped is questionable, but without the bleed hole, it could potentially get trapped in the pump area. (And allow for cavitation).

If you do block the bleed hole, and you've drilled a hole in the stat, it has a very similar effect as the bleed hole. But as some have mentioned, you may not reach full operating temp in use. And, it's possible air could get trapped in the pump housing area. That bleed hole is really to prevent air in the pump housing area.

Not reaching temp is undesirable for emissions, and for removing moisture from the oil/engine. It could also prevent the heater from reaching full temps too.

Stats don't slam shut or open fully instantly, that you need to keep in mind too. So in theory, even without the hole the air would bleed out to the rad.

The only case that air MIGHT not bleed out the rad is if the rad cap is lower than the stat housing or is lower than the highest part of system. Even then, believe if eventually will bleed out.

Coolant is under psi in operation, have to keep that thought too. If it weren't under psi, not only would the coolant boil at a lower temp, but you can have 'pockets' of air around high(er) temp areas, like the cyl and/or heads/chambers.

Which brings up the 'Pontiac flow mods'. Some believe it's advantageous to reverse the flow of coolant and/or have the coldest coolant pass thru the heads first. To have efficient combustion, you have to have heat, so personally, believe the mod is worthless/counter productive.

Just thinking out loud here...

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[chuckies76ta]

Awesome, Thanks for taking the time to reply.