This past weekend, I took my 1992 500E on a trip up a local "mountain" (Mount Diablo). Travel up to the 3800ft summit required travel along a long windy road. Ambient temperature was about 70 degrees (fahrenheit). After parking the car near the summit, I heard a gurgling sound coming from the engine compartment and noticed coolant leaking under the car. Lifting the hood, I could see that the coolant was "boiling" in the coolant resevoir, and being forced out through the overflow tube. I lost probably a half gallon of coolant as a result of the overflow.

When I started the car, the gurgling stopped. The temperature showing on the guage was what I would consider normal, given the trip up the mountain (between105 and 110). The gurgling started again when I cut the engine. When the gurgling completely stopped, the coolant resevoir was pretty much empty.

So what happened here? Was the car overheating but not registering on the temperature guage? Do I have an incorrect coolant/water mixture in the cooling system? Does the fact that fluids boil at lower temperatures at high altitudes (due to the lower pressure) explain the problem? Does Water Wetter have an adverse effect at high altitudes?

Any thoughts would be appreciated.

Thanks,

John