Originally Posted by drh1965
I've got a petcock mounted in the thermostat housing of my Universal M18. It appears to be a device for bleeding air out of the cooling system. Unfortunately, it is not mounted properly and does not function. Is bleeding the air out of the cooling system critical?
I've got a new petcock but the existing one is incredibly stuck in there and made of brass. It deforms easily and I'm afraid I'll wind
up breaking it off...
It is good to get all of the air out of the cooling system (I'm assuming that you have fresh water
cooling). Air can get much hotter than water
. If you have 300* airbubbles circulating in your system, that is far worse than having 212* water or 225* water/coolant mixture. It also takes air for water to boil. If you can keep all of the air out, you lessen the chance of boiling.
Now, having said all that, if your engine
gets hot enough to expell expanded water out of the radiator cap, air will be ingested, after the cooling system cools. That's why it is importnt to have a recirculating overflow tank. The water that expells goes into the tank, then as the engine
cools and the expanded water contracts and causes a vacuum, it will suck the expelled water back into the engine instead of air.