Altitude and the coolant reservoir

[awolff280sl]

On our way back south from Blacklick we went through the mountains, and I don't think we were any more than about 3500 ft above sea level along the way. One morning along the way, with the engine cold, coolant in the reservoir was low. The fluid level is normally about an inch or two below the neck. I refilled it with about 16oz and it's stayed there since, now at sea level.
Can anyone confirm that this is due to the altitude change? I am assuming that the altitude caused fluid loss from the overflow pipe. If so, how do modern car systems avoid having to refill when going back to sea level?

[Peter van Es]

I've had the same thing happen to me when rallying in the Alps. I observed the same, after adding coolant I never needed to add more. It's weird, as because of the decreased air pressure coolant should appear fuller, but it did not. I have no explanation for it. Maybe it is related to the fact that after driving up a mountain, during which your engine has worked extra hard, more coolant gets dissipated.

Peter

[al_lieffring]

Andy

the second part of your question, What is different on modern cars is that the overflow goes into a catch tank and when the motor cools the fluid that escaped gets siphoned back into the system.

[awolff280sl]

Thanks Peter, reassuring to know someoneelse has seen this.
Thanks Al, now we've got an item for the mountain maintenance schedule.