I have an 83 300SD an the temp consistently runs 80 to 81 degrees C in the winter and about 90 Degrees in the summer.

I notive that if it is below say 20 degrees and my car idles for more than 10-15 minutes it cools down to about 65-70 degrees, is this normal? I am referring to the SD.
Thanks
David

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2000 Honda Accord V6 137k miles

1972 300SEL 4.5 98k miles

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mine runs 'slightly cooler' not by a lot but it is noticeable.

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1984 300D Turbo - 231k....totalled 11/30/07 RIP

Both of mine run the same temps regardless of outside temperature but, they have their quirks.

The 300TD runs 90°-95°C at any speed above idle until you turn the a/c on, at which point it drops to about 85°. During extended idling (heavy traffic)with the a/c on in ambients above 95°F will cause the gauge to slowly creep toward the 100°C mark. But, I've never actually seen the needle touch the 100° mark.

At speed, the 300D always runs a needle-width above 80°C with or without the a/c running. Idling in high ambients it too will creep toward the 90° mark.

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Never a dull moment at Berry Hill Farm.

once it's warmed up, the temperature guage on my '83 Toyota Celica (22RE motor) moves about the middle 3/8" of its range, very clearly indicating the functioning of the thermostat. It does go a bit higher than that for a few seconds during the warm-up, as if the thermostat opening is delayed somewhat at first, although some have said that this can indicate a small head gasket flaw -- that it doesn't hold cylinder pressure perfectly until it gets warmed up.

To a point, yes. The thermostat is really serving two purposes: it prevents cooling from occurring until the coolant reaches its opening temperature, then it opens to create cooling to maintain optimum operating temperature. I know that at least for my OM617 the proper thermostat is one the opens at 87 C. I take that to mean that the minimum temp that Mercedes wants my engine to be is 87. During warm weather my car reaches that within 2-3 miles of driving. In colder weather - say 20 F or less - it takes longer. During the recent cold snap I was up north, and it didn't get much over 82 or so until I got on the highway. And, in response to the earlier comment, a diesel at idle will cool down if you leave it long enough in cold weather. 60 seems a little too low, but I suppose it depends on how cold it is and how long the car's left to idle. They use so little fuel that little heat is generated. It's also my understanding that there is increased engine wear at cooler temperatures.

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Tjohn

82 300 SD
77 450 SL (gone)

Also, the engine block, cylinder head, intake/exhaust manifolds, valve cover, and oil pans all act as one giant heat sink (Think how a computer CPU keeps cool). Even when very cold, that fan is still spinning and moving air into the engine bay. Even if you make a main electric fan that can shut off, it will still have the heatsink effect due to heat rising.

I had an '82 Datsun diesel p/u with the SD22 diesel engine and it always ran at the middle of the gauge no matter how cold or hot of a day it was running in once it was warmed up. My wife's 92 Camry and my '89 Toy p/u that we used to have were the same.

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DJ


84 300D Turbodiesel 190K with 4 speed manual sold in 03/2012

My Mercedes doesn't run any cooler, occassionally it seems to run a few degrees warmer, but always under 100C. It takes longer to warm up when its cold.

My Dodge Cummins pick-up takes a LOT longer to warm up when its cold and it sometimes cools down if I'm idling (once its warmed up).

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Brian Toscano