i thought it was 100c, but ??

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81 240D: Lola
77 toyota chinook: Carlito
93 chevy k1500: Cowboy

right, none of my 240s have had clutches, this one no exception

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81 240D: Lola
77 toyota chinook: Carlito
93 chevy k1500: Cowboy

For an additional data point, at any temperature under 90F or so, my engine temp stays at 82C. At anything above 70mph, it’ll sit at around 85C. Under full load, going up an extended grade, it’ll creep up to about 90C, but no further.

For temps above 90F, in and around town, 82-85C. Highway above 65mph, 90-95C. With A/C or extended grade, 95-105C.

Was recently on a 9 hour journey from north to south CA. Average temp outside was about 98F. I drove about 70mph, with AC on max. Engine temp was at 100 the entire time.

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1981 240D 4sp manual. Ivory White.

You could be right, I'm just not positive myself. If 90c is where is 'should' be, then id be surprised there wasn't a line there.

80, 90, 120...? In equal increments?

It’s 100, you can rest assured.

About 82-85 is normal, but there are many variables to consider. This is why MB lists an acceptable temperature range. The thermostat you have installed should be rated at 85C.

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1981 240D 4sp manual. Ivory White.

this sounds like the experience i'm having now, and it also is the same as other owner's in older posts -- its not doing damage, as long as i'm below 120, but i would prefer to have it lower, particularly when the doctors office is 2000' lower than us on the continental divide, and its a regular trip -- and then going up to 10k' for hiking, etc. -- so i think i'll see if i can get the temp down -- i'm not willing to do the whole citric acid block flush, cause i see no corrosion evidence, but i will take out the radiator and flush it, and maybe have a look at the pump -- but first i'm trying the new cap out

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81 240D: Lola
77 toyota chinook: Carlito
93 chevy k1500: Cowboy

i think the one i put in is rated for 80 -- i know the old, oem, one was

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81 240D: Lola
77 toyota chinook: Carlito
93 chevy k1500: Cowboy

Do post your results!

It never seemed like a water pump issue to me. Radiator cap, I’ve yet to try.

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1981 240D 4sp manual. Ivory White.

definitely will(don't care for folks getting lots of input, then not sharing their results)

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81 240D: Lola
77 toyota chinook: Carlito
93 chevy k1500: Cowboy

O.K, I'll chime in here because I too have one, a 1982 240D automatic that I load up and drive all across the Southwest and yes, @ 60 ~ 65 MPH it gets up to 90* C with four people in the car and the AC on .

You're in New Mexico so that's not running terribly hot .

Failing to flush the entire cooling system is a fools errand because there is always accumulated silt & sediment in the block .

It's easier to flush everything at once too, far easier than removing the radiator for separate flushing .

We just came back from Nevada where we had some 113* days, then the temp gauge got up to 100* C but no higher and cooled back down rapidly once parked in the shade .

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-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

"facts & reality don't change because you can't handle them"

ain't that the truth

thanks for the input, it is helpful, and i will take it into consideration

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81 240D: Lola
77 toyota chinook: Carlito
93 chevy k1500: Cowboy

well, it wasn't the radiator cap -- onward!

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81 240D: Lola
77 toyota chinook: Carlito
93 chevy k1500: Cowboy

I think "everyone" may be being somewhat imprecise. For the car to run at 80C the needle should be on the white line next to 80 on the gauge.

The next white line between 80 and 120 is 100C and the last line with the red on top of it is 120C. So for the car to be running at 90 to 95C the needle needs to be covering the top of the 8 in the 80C, to just about to leave the 8 altogether. If it reaches the unnumerated white line half way between the 80 and 120C you have reached 100C.

I have never seen a Mercedes that runs at 80C. Look at the cars in my signature. These are gassers and diesels on two different continents and they have always run with the needle in the 85C to 90C range under normal conditions.

My DD, also an 81 240D is currently running probably too cool. The needle is just above 80C so likely around 82. This is a recent development and I think likely because of a stuck thermostat which I will soon replace. I had the same symptom on my previous one which was fixed with similar results.

I have not climbed in the mountains as you have, where are you located? Anywhere near Las Cruces? But I drive around in Phoenix and with temps regularly above 112F ambient and would not be concerned in normal driving unless the temperature started to get towards the half way line, ie, 100C.

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

Coolant Temperature Gauge

Due to the pressurized cooling
system, the coolant only starts
boiling at a temperature of approx.
257° F (125° C) with an antifreezeblended
coolant fill protecting down to - 2 2 ° F
( - 3 0 ° C)

During severe operating conditions
and stop-and-go city traffic the
coolant temperature must rise to
red marking only.

yes, it would be more accurate to say that some owners reported this, but that others had other reports, and some were similar to my current experience

this situation may have existed for years, and i never would have seen evidence of it, since i wasn't climbing -- if i'm not near the red, i don't pay much attention -- in ajo, az, was hot like phoenix, but we would leave come 6/1 -- now here in silver city, nm, is different -- we're here year round, this is our first summer, i went from 6000' to 8400, and noticed i was up around 110

with the infrared temp gun, i know that my 80c thermostat is opening around 85, as measured on the thermo body, so 90 operating temp on the gauge probably is normal for this thermostat

my attitude now is i can live with it, but i'm going to take a shot at lowering the temp, with a citric acid flush -- i know that when i replaced the radiator in my old 6.2 diesel van, there was a dramatic drop in temp

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81 240D: Lola
77 toyota chinook: Carlito
93 chevy k1500: Cowboy