Wifey overheated the wagon today. No damage apparent, once it cooled it started and ran fine, but was down almost 2 gal. of coolant. It's not coming out of the tail pipe, it's not in the crankcase. Radiator looks good - no rust or anything else. No leaks in any hoses that I can see.

The only thing is that occasionally, it benches alot of coolant out of the overflow tube from the tank.

It had done this several times over the past few months, including last night.

What is the problem here?

Thanks!

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT