You're correct the antifreeze will not circulate if the thermostat is closed and the other commenters are correct also, adding water will totally DESTROY the engine, it causes RUST on the inside of the engine it is probably one of the worst things you can do to an engine, it's as bad as never changing the oil. Tell your brother to get under the truck and to drain the fluids out of his radiator via the plastic drain plug usually on the drivers side bottom of the radiator and replace it all with fresh antifreeze 50/50 either buy it 50/50 or mix it 50/50 with DISTILLED water. You can get it at the grocery store for less than a dollar usually. Probably be a good idea to replace the thermostat as well since I'm sure it's covered in rust too.

Hello

It will circulate around the engine block because of the Water Pump. When that gets warm the Thermostat opens and it then circulates around the Radiator as well to give more cooling

Think of it as 2 boxes with 2 hoses connecting them. The top hose has a On/Off tap (Thermostat)

Andy C

Andy C

Running water in a cooling system is the single best way to destroy your radiator, water pump, and heater core. Coolant contains anti-corrosive additives that stop electrolysis.

And you're right, coolant doesn't circulate when the T-stat is closed. Well, it does flow thru the heater core, but not to the radiator. As soon as he takes it for a drive, it'll all mix.

Probaly be OK. The thermostat don't seal perfectly so some water circulates even when it's closed. 5 mins should mix it around pretty well.

BTW, you should run antifreeze in the summer as well as it also prevents corrosion, especially with alloy engine components, which most modern engines have.

you have two stages of flow in a cooling system like that. you have recirculate where the coolant is not allowed to the radiator just yet since it is blocked by the thermostat. it goes back to the block until it is up to the temp that the thermostat is rated it.

It does not. He should have warmed it up. I wouldn't want to get a hard freeze like that.

If the thermostat is closed, will coolant still circulate in the water jacket? I am asking this because my brother was only putting water in his truck during the summer and he added antifreeze tonight and only started his truck for about 5 minutes. I told him if the thermostat is closed it wouldn't circulate in the block. Is that correct?