upgraded water pump? w123 300d
 

probably going to buy a replacement water pump soon (car slowly heats up at red light, cools down when driving, but gets hot again under heavy load at speed).

i seem to recall someone mentioning water pumps from certain years were preferable (better impellers) or there's an upgraded version... or something like that.

am i mistaken?
im probably not remembering correctly... probably confusing it with comments about fan blade material or something.

Is this something new to your car? How hot does it get and what is the ambient temperature?

I'd replace the thermostat, clean/flush the cooling system with CRC ThermoCure for that symptom before changing the water pump.

That sounds more like a bad fan clutch to me.

I would think at speed means interstate travel at 70+ which should negate the fan clutch. Have you looked to see if there is any debris between the condenser and radiator?

Agree at speed equals a radiator issue or a thermostat partially open.

+1 sounds like a new radiator to me.

There are several types of water pumps out there.
Some with Teflon coated cast iron impellers, some with stamped steel...

Guess which ones rust away and stop flowing...

A company named Brassworks in San Luis Obispo, CA. makes water pumps with the Teflon coated cast iron impeller that provides superior flow and durability. You may want to check with them to see if they offer a water pump for a Mercedes 300D. They have a website: thebrassworks.net

Summer Cooling Thread
 

Agreed ,

Before anything else do a Citric Acid clean of the entire cooling system .

The Teflon coated impeller sounds interesting, I hope you try one and take and share pictures .

Given a regular 'ol pump works fine, I wouldnt expect too much from a uprated pump.

I agree with others that suggest looking at the radiator.

I tried everything when my 1985 300D was overheating, but the symptoms were different. It would overheat at long stoplights on >90 F days, but never when driving at 35+ mph. I never took it on steep long grades in the Sierras. I tried several fan clutches, T-stats, citrus acid flushes, used radiator (flushed well), even removed the T-stat housing looking for something plugging the flow. Finally bought a new radiator when found affordable price ($130 vs $350 before) and that solved it. Tore open the old radiator and found a thin coating of "metal mud" covering the tops of most tubes. It flaked off easily, so surprised it didn't work when I ran a SS grill brush over the tops. The new radiator was also an aluminum core, said to cool better.

'Worn Out' Radiators
 

Same thing in my beloved 1982 240D ~ I'd flushed the beejesus out of it and could see the tubes were wide open yet it still ran above 82* C no matter what and occasionally crept up to 100 + * C on hot days os in Death Valley etc.

So when NISSIN dropped the price of the new radiator for under $300 I ponied up and Lo ! it never tops 90* C no matter what anymore and yes, it blows plenty of heat when I want it to .

Us older guys are accustomed to brass / copper radiators you can sweat the top tanks off of the 'rod out' using delicate flat 'rods' that scrape all the coating of rust and crud off .

This should be pinned to the top of the board.

When I was having overheating issues, it seemed like replacing the radiator was akin to yelling uncle. It’s the most obvious and integral part of the system but for some insane reason, you get people suggesting faulty temp sensors, pin hope leaks in hidden conduits. telling you the 11th citrus flush should do the trick, and so on!

Replace your 40 year old radiators!!! :)