Real time help - Temp Problem?

[flintknapper]

My brain's torn on theory about the expansion tank... When the fluid is hot and expands, it would divert to the tank making it 'full' while hot, and not work the other way around like a vacuum drawing it out of the tank, correct?

The overflow tank is supposed both accept fluid (hot, expanding fluid from the radiator) and replenish the radiator (when the everything cools down). This is a function of your radiator cap which is a two way pressure valve basically. When the pressure (related to heat/expansion) reaches or exceeds the spring rating of the radiator cap...it pushes the seal upward letting fluid flow into the overflow tank.

When the fluid cools (less fluid volume) a vacuum is created and the smaller seal (at bottom center of the cap) is pulled down allowing fluid to re-enter the radiator.

 

[flintknapper]

She'd been very low, about 3qts. Expansion tank is full when hot, so I know it's not empty by any means.

Very important to make sure your radiator is full at cool down. Fluid in the overflow bottle is only evidence that at one time the radiator cap allowed expanding fluid to travel to the Overflow. BUT if your radiator cap is/was faulty or the the line going from the radiator to the overflow reservoir is plugged (or the OF cap itself) then fluid can not come back to the radiator. The radiator gradually loses volume. The air space above the fluid in the radiator can then become very hot!

Of course, a 'leak' in a hose (sometimes a pin hole) or the water pump will gradually deplete the fluid level as well. So just check everything out real well.

 

[abuck99]

For the expansion tank to work properly- the cooling circuit cant have any air in it.

For the next few days, remove radiator cap 1st thing in the morning when its cool and check that its full to the filler neck. Keep adding coolant to the main tank as necessary until it stays topped off. Then keep an eye on expansion tank. I keep mine 1/2 way between empty and full when cold.

Burping radiator: I use one of these;
Amazon product ASIN B01I40ZQWE

 

[MongooseGA]

Thanks to both of you gentlemen. I'll check it again in the morning and keep it a habit for a few days.