Just drove our 85' 300TD across country from NY to CO (3800 miles, was on my bucket list) and only a few problems on the trip. First the cruise control quit on the second day, next the seal on the rear of the SLS pump leaked after only two years after being rebuilt. And lastly it overheated when climbing into the mountains over 9000 ft. The first two things I can understand, and we rebuilt the pump once out in Denver. So not a big deal, but the overheating has me wondering what could be wrong. Had no issues going out west at temps in the 90's with the AC on, but when we started going up into the mountains the temps went whey up and she started to overheat out the overflow tube on the tank. Also the car does not like the thin air out there, was a real dog till the turbo spooled up. Not like here at 500 ft. above sea level. My thoughts are maybe the thermostat is bad, or the water pump might be bad. My plans are to replace both, but I don't think I can duplicate the same conditions here to see if I fixed the problem. Anyone have some thoughts on what could cause the overheating?

Attached Thumbnails

   

__________________
Von
Fairport, NY
1973 Unimog 416 Doka
1980 Unimog 416 Doka
1981 Unimog 416 Doka
1984 Euro 280CE w/diesel conversion
1985 300TD Estate wagon
(I really need to stop buying these things!)
http://vonsmog.com