I'm really sorry if this question's been done a million times ... I used the search and found some info, but wanted to check to make sure I know the right answer specific to my car.

On my way home from a road trip, I have to cross the Nittany Mts., which is a pretty good climb. My car (87 300D) generally runs at just above 80c, sometimes up to 90 (this seems to be consistent in winter and summer times). While I was hiking up the steepest, roughest part of the drive, it was rolling just above 3,000 rpms and sounded pretty good, but the temp climbed somewhat quickly to 100, maybe even a little higher. It gradually dropped back to a little above 80 once we hit the downhill again and stayed there. I would assume this is normal when the engine is under a heavy load, such as climbing a mountain, but I never want to assume TOO much, so I thought I'd ask. I have heard all the cracked head horror stories on the 603. I have been warned many times to immediately back off if this car starts to overheat. ... is there a specific temp at which I should ease off a little? I don't really want to find out by pushing it until I see smoke billowing out of the front!

I hope I don't ask too many questions, esp. ones that have already been done before. But you guys give me great answers, and I have learned a ton from this forum. A year ago I couldn't have told you a thing about cars, and between this group, my mechanics and my dad, I'm approaching competancy. Hopefully someday I will have enough knowledge to "give back" to the Mercedes community instead of just asking 5 million Qs.

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1987 300D, arctic white/palomino--314,000 miles
1978 240D 4-speed, Euro Delivery, light ivory/bamboo--370,000 miles
2005 Jeep Liberty CRD Limited, light khaki/slate--140,000 miles
2018 Chevy Cruze diesel, 6-speed manual, satin steel metallic/kalahari--19,000 miles
1982 Peugeot 505 diesel, 4-speed manual, blue/blue, 130,000 miles
1995 S320, black/parchment--34,000 miles (Dad's car)