How do I get air out of the cooling system?

[luigisho]

I had a little mishap the other day with a bit of overheating/coolant loss through the surge tank. The motor runs well except I think I have air in the line somewhere. The temp gauge doesn't read right and jumps up and down from the top of the L to the bottom range of -C(old). When the temp is close to a presumably normal reading performance is much better. How to be sure to get the air out of there w/out opening it up???

 

[sdpatt]

It sounds as if you may not have the B series Motorcraft theromostat with the jiggle valves. The purpose of these valves is to help vent the trapped air when filling the system. The air will be naturally discharged to the expansion tank and replaced with coolant as long as the expansion tank is not allowed to run dry. These vent/fill cycles happen as easily as when the radiator fan actuates. All it takes is a small change in temperature in the cooling system to vent and fill. You can watch for bubbles in the expansion bottle as the engine warms to see if there is any air left in the system. Just don't drive the engine hard until the air has been purged and the temperature gauge is back to normal.

 

[tomw]

There is a tool available that evacuates the cooling system down to 28" vacuum (similar to what is done to an AC system). Then it refills the cooling system with a 50/50 mix of your favorite coolant and water. Gives a total fill every time with no air left in the system. Mine was made by MightyVac and cost around $100. Works great on those hard to refill systems that always get air locked. I am starting to see them in gas stations.

Tom W

 

[Mike Kopstain]

If you want to do it immediately and not have to look through the overflow bottle, just wait for the car to cool. Once it's cool take off the radiator cap and start the car. Turn the heater on full blast. If you look in the fill tube, you'll see the coolant lower and raise and you'll see it bubbling. Once it stops bubbling the air is out. It is important however to make sure that the T-stat has opened while during the procedure. Good luck. We had the same problem in the 94'. It would go up to Red and then down to the L. Bleeding it fixed the problem.