revitup

'77, L-82. Coolant overflow tank with the two ports on the cap.I'd sure appreciate it if someone could help with a problem.
A significant amount of coolant flows out of the overflow tank vent after shutdown. Coolant system was pressure checked, all leaks corrected. Coolant changed. Changed the pressure cap. Replaced the small section of hose in the overflow tank. Checked that the hoses to the overflow tank are routed correctly. Checked radiator level when cool, it's full. Overflow tank is at about half full and it seems to stay there.
I could use some suggestions as to where to look next to correct this issue.
Wouldn't coolant have to fill the overflow tank before it could exit out of the overflow hose? How does that happen with the tank only half full?

Jamess411

As far as I know and from experience the level in the overflow tank should be half way when it is cool…not full…assuming all the air pockets have been bled out…..that is where the expansion from the heated up coolant goes. When the car is shutdown after running and the coolant stops moving is when the temp is generally the highest and expansion the greatest. So stop filling up the coolant when it is cool and let it naturally find its full level. After running it check to see where it is…if it is half way after cool down you are set.

revitup

James, thanks for the reply but I think you misread part of my description of the issue. The radiator is full when cool, not the overflow tank. The overflow tank is only half full. The coolant is expelled from a half full overflow tank at shutdown. I can't understand how that can even happen.

doorgunner

I had the same problem.....the coolant may heat up rapidly (like Old Faithful) and jet itself out of the overflow tank without actually filling the tank up......that happened on my car. I had to add an aftermarket "overflow jug" to the system by connecting a longer vent tube to the jug. Now no coolant goes on the garage floor....and when the engine cools down it siphons coolant from the jug back into the overflow tank.

(Of course you know to first repair/replace anything that could be causing violent overflow at the vent tube before adding a "jug")I did have a new thermostat that would stick closed 50% of the time)