I ask this because I want to make sure my car is not hotter than normal around here. My 83 300SD typically operates between 95C to 105C--at the lower end on the highway and at the higher end in city traffic--during the hottest time of the day. At night, I get 85C to 95C. One of the MB shops around here said that with the A/C at max setting I should be around 105C (normal) in this weather.

So what temp do you usually run at?

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1983 300SD (W126, OM617) with 404k miles!
(OK, so the engine was replaced at 147k mi)

Can't comment on AC operation as my 240D's compressor seized before I bought it. I've driven thru two Phoenix summers now without AC...

At no stage has my car's temprature needle ever left the 8 of 80C. So I guess that would put it at about 90C, that's while idling and in stop and go city traffic with ambient temp's above 110F. Of course that's a 240D and no AC so don't know how applicable it would be to your vehicle. Interestingly this behaviour has remained consistent between my old leaky radiator and the new one I just put in it a couple of weeks ago.

- 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

No AC!? I'm not sure I want to test the engine temp with the AC off when the ambient temp is over 110F. Still, your temp is lower than I would expect even without AC.

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1983 300SD (W126, OM617) with 404k miles!
(OK, so the engine was replaced at 147k mi)

My 82 SD runs right at 80 degrees C on my morning commute with ambients in the 80 to 90 deg F range. On the ride back home with temps in the 110's I get up to about 95 degrees, and get really concerned as it approaches 100 deg C.
As part of my complete maintenance overhaul, I plan on replacing the radiator, all cooling hoses, and expansion tank. In our area of the country you can't be too careful.

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1989 300E
103,500 miles

1982 300SD
Sold but not forgotten

On a 1981 300SD, original engine and radiator at 255,000 miles, in downtown Phoenix, I get about 90c with the AC off and about 105c with it on. It's a high number but this is summer #3 with this car, and my old boss at German Auto Repair used to say, Mercedes designed the gauge to use all of it... not in the red, you're OK. The owner's manual actually states words to this effect. I think yours is A-OK...

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1985 300TD
1984 380SL
1983 280SE (full Euro, trunk triangle and all!)

Formerly owned:
1986 420SEL
1984 300D
1983 300D
1981 300SD
1976 300D

My 300D has a fairly new radiator, on a recent trip the temperature stayed between 85 and 95C on level ground at highway speeds (75-80 mph, 105F ambient). It would creep up to about 100C on very long/steep hills. With the old radiator it would have been about 5C higher. It can get a tad higher in traffic, maybe 100-105C at worst (be I spend very little time in traffic).

Yours is probably normal and I don't think you are hurting anything, but if it bothers you do a good system flush and toss in a new radiator to get a few degree improvement.

I get max temp. when cruising on the interstate at 80 mph with A/C on max. Temperature needle hasn't exceeded 100C this summer. As soon as I pull off the interstate, it drops down to the 80-85 range.


Who is it that has the quote in their signature "If it ain't broke, fix it till it is"? I know if it were me, I would end up damaging some of the old fragile parts that have taken a permanent liking to their current position. I would leave it alone.

K.C.
84 300D
258k

I don't live there, but did spend a few days there on a recent vacation road trip. My W210 diesel kept right at 80 while traveling about 75mph on the freeway. In town stop-and-go traffic it would get up to a little below 90. It never passed 100, even on hard acceleration up ramps, etc. All of this was with the AC blowing hard and the ambient temp comfortably above 100. The highest reading I saw on the car's outside temp indicator was 117 that week -- probably not really that hot, but probably accurate for being on the blacktop.

Cheers, John

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'98 E300TD (W210) | Sold 6/09 with 205k and counting
'04 VW Touareg V10TDI

I live here in the East Valley and commute daily through Phoenix and my engine temps are right about 100C in city driving and about 90C on the motorway with the AC going full blast so I think your OK! I just put in a new radiator from Phil and changed my cooling system hoses and anything else that looked questionable. I also replaced my AC refrigerant with Envirosafe ES 12 and that makes my motor run a little cooler since the compressor isn't working as hard. Just keep checking your coolant and carry water with you and you should be fine.

I like that quote. Replacing the radiator in these things is so simple a caveman could do it.

does it matter if the a/c is on full blast or low? I thought that the compressor on was all that mattered in regards to engine temp.

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Andrew Villasenor
805-720-5057
1984 300D turbo 5-speed manual(daily driver)
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