I have just bought a 300D and noticed that the cooling system registers over 3/4 of the way to the 120 measurement. It cools down to a little less than that when driving down the road. Would this be considered a normal operating temperature for this vehicle?

Thanks!

My 300D is a 1983 with 204K. I guess it is running about 110C when sitting still and 90C when rolling down the road.

I'm not sure of the year of yours, But mine runs at about 82C.

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92 300D 2.5L OM602 OBK #59

You should add the year of car and the mileage to your signature and your
location to your profile. Helps to know where you are !

The folks in North Canada and Alaska have different results than the Arizona
and Texas desert folks.

Now...

Running at a solid 80/82c in all temps is not uncommon.

If the radiator and cooling system are flowing perfectly and are not clogged
you can still get an engine that runs up when stopped in traffic.
Might go as high as 100+c almost 120c.

For mine it was the radiator fins clogged up and needed to be cleared.

It was really, really easy to pop out the radiator and clean out the fins.

There are products to dissolve crud.
I used water pressure, and air pressure and a shop vac to work all the junk
out and get the fins cleared so the air could get through.

My car runs a solid 82c even in 100+F .

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250

my old one with 215K miles kept it at 80c all the time with the rubber o-ring about shot so alot of bypass. When i changed to new one it crept higher going to about 85 to 90C at times. so i'd say anything close to that would be good or u could always find someone with infra-red heat gun and check..

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2004 Infiniti G35 3.5L 6mt Coupe 73K miles 25.6mpg ytd
2001 Green Audi TT 225 AWD Roadster 71K 6sp 30.9mpg >>STOLEN<<
1982 300D Turbo 231K 120hp? 28.1mpg YTD

80-85*C is where it would always stay once warmed up. If your cooling system is in proper condition, only on a hot summer day with the A/C running full blast and sitting in slow traffic is when it should ever be acceptable to reach 100*C.

Here is a good check list to get the cooling system where it should be:
Check the fan clutch for proper operation. It should lock up at 95*C and audibly move more air.
Ensure the electric fan comes on with the A/C.
Blow out the outsides of the radiator and condenser from both sides with a pressure washer until only clean water comes out.
De-oil, citric clean and flush the system.
Install a new 80*C Behr thermostat.
Use MB or Zerex G-05 coolant in a 40/60 or 50/50 mixture of coolant/distilled water.

Optional:
Replace the stock large (1.09:1) pump pulley and aluminum fan with the updated smaller (0.9:1) pump pulley and 9-blade plastic fan.