So I just had the a/c fixed on the benz and it wanted to make sure that I was thinking clearly. Before I had the a/c fixed the engine ran at about 90C-100C. I run the MB coolant with water, about 50/50 and a bottle of water wetter. Now keep in mind this is TX and it gets really hot, about 101 today, but now since the a/c is working it is running at 110C. I know that the temp should rise with the use of the a/c but should I be worried? The temp does go back down to 100 if the a/c is turned off, and gets to about 115 when doing approx 70 down I35( I promptly turned off the a/c and slowed down when it hit 115). In town the temp hovers in between 100-110, with the a/c on. I am leaning towards flushing the cooling system and I have made sure that there is nothing interfering the air flow. Is there something that I am missing, or is this just the combo of TX heat and the diesel engine producing the high temps?

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1980 300D European
"The Red Fox"
200,000 miles

2003 Chevrolet Silverado

609 Certification

the higher temps at freeway speeds and lower temps in town could possibly indicate a blockage in the radiator.

Bring it up to temp and turn it off.
Stick your hands into the the shroud and feel for cool (a relative term) spots.
is you have uneven temperatures a rod and boil might be in order or a citric acid flush might get some more efficiency.

you should be careful when you do this.

you might have air in the system too. that causes wacky temp fluctuations

Is your AUX cooling fan working?
If it is, continue reading.

#1. Replace thermostat.
#2. Remove the radiator; have a radiator shop flow test and flush it.

__________________
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1985 300SD
1983 300D
1984 190D
2003 Volvo V70
2002 Honda Civic

https://www.boldegoist.com/

Yeah isn't that thing supposed to turn on whenever the engine temp reaches 100C?

My 300SD ran warm until I replaced the thermostat.

www.benzbonz.biz

Marty

This has been discussed over and over...his is a 1980 w123 body 300D...

The answer? No.
Its part of the AC overtemp system, not the engine. You can search.
On average, if you let your car sit idling (no air flow due to road speed) with the AC on, the condensor (and thus AC system) will get hot enough to kick that fan on

You can test if it works by jumping across the contacts on the AC dryer..

forunately my aux. fan does work, so I will replace the theromstat tommorw, rahter today, and test as well as have a complete cooling system flush to ensure the is no blockage. Since both of these steps are not expensive I dont think it could hurt by completing them.....unless there is something I am missing.

__________________
1980 300D European
"The Red Fox"
200,000 miles

2003 Chevrolet Silverado

609 Certification

I just had similar symtoms to yours in my 300SD.
Everything working great, the radiator is clean and flowing nice.
I did a citric acid flush, offed all the old water/green juice and put in some nice fresh orange in a 50/50 ratio.
I pulled the thermostat while I was flushing the green out of the block and it seemed okay.
I still climb when it gets real hot....
The aux fan works okay...but I can still float up close to 120C if the conditions are right.