I've had a 1987 300SDL for... oh... almost 2.5 years now? The car has mileage: 250k, yeah. I dearly love this car, and have invested huge chunks of change into it time and time again. Transmission, front suspension rebuild, engine mounts, an oil pan (my bad), cosmetic details... when I bought this car I was expecting to pour ~$10k into price + fixes, and to basically have it not need any work after that. Well, I've poured that money in, but theres one thing I have not addressed, and this really should've been the first thing I looked at.

My car overheats going uphill. The cooling gauge stays around 95C during non-winter months, and when I go uphill, it starts slowly steadily rising. Its slow, but it doesnt seem to slow down as it heads into the red.

On the east coast, this would not be a problem. I, however, am in the rockies, and we have little but mountains.

What possible causes are there for this? Are there remedies? I love this car, am happy to pour money into fixes, but this is one of the rare issues where I dont know what if anything can be done. Is this symptomatic of all old diesel benz's? Is there anything to be done, or is it just an old tired engine?

I had a bad incident trying to get out of an offroad camp site 20 months ago, where I was so busy trying to get over a hill I didnt notice that I was drastically overheating. I'm a bit hazy on recalling the details, but something in the cooling loop blew a leak, and I had to feed it water until I got to the city. They replaced, amongst other things, the thermostat and the cooling loop impeller. Of all the things I'd suspect would be the cause of cooling issues, those two are are the top of my list. I'm tempted to take out the thermostat altogether: the work lost to constantly pumping coolant seems a worth sacrifice to possibly keeping it cool.

This is absolutely critical to me. This has been an issue with the car since I bought it, and I should've figured it out then, but for whatever reason I never have. If this is not a resolvable issue, I'll have to sell the car, even though I've already invested a ton of money under the assumption that I'll be driving it for another 150k-200k. What should I check, what can go wrong, what can I fix?

There is a local Benz shop I trust greatly, but in this particular issue I feel the need to reach out and figure out what I'm dealing with.

Thank you for your time and consideration,
rektide