...have noticed for several years that the temp gauge (240D) runs a tad cooler when it's REALLY cold out. Anyone else?

It's likely running at it's "proper" operating temp. The colder air flowing across the radiator keeps the coolant cold enough that the thermostat only opens a smidgen at a time.

When it is cold I will often see the temp gauge fluctuate up and down slightly. I assume I am seeing the thermostat open and close. My duramax shows it more clearly than the benz does, but I can notice it in both.

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Keep everything as simple as possible-but no simpler--Albert Einstein

82°C in the winter... don't know about the summer yet.

Yep.......

Runs 81-83 when very cold out unless it thoroughly warms up at 3000 rpm for 15 minutes or more and then it might get up to 87 or so.

I warmer weather it runs at a steady 90 after it warms up.

In hot weather, with the a/c on, it can reach 100, especially if the turbo is working.

Just an aside to this thread, I remember a member posting awhile back about temp gauges in Japanese cars and how he wished they operated the same way in his Benz. That is rising to 190 and staying there rock solid never moving no matter what the outside/inside temp may be. I just read an article in an English car mag that stated the temp gauges in Japanese cars are more like "idiot lights" than anything else. They're so heavily damped so as not to confuse the car owner and having them come to the dealer every time their gauge moved up or down. I never knew that.
Actually, last summer(my first summer with the car) my 81' 240d ran cooler, say 80c instead of a little above when I had the aircon going. So I knew if I wanted to cool the engine down alittle all I had to do was turn the air on.
Winter time it's seems to be fluctuating normally depending on road conditions,speed.

punky,

New Volkswagens are the same way. The temperature gauge won't budge off of 190°F unless you're overheating, in which case it will move quickly towards the upper end of the gauge.

Mercedes-Benzes have temperature meters (accurate measure of temperature) as opposed to a gauge (estimate/idiot gauge).

my 300TD runs cooler on cold temps or at night with a cold breeze.. it is a tad higher than the 80deg mark. On high noon and hot temp, my temp rises to around 90deg.

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Mike

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1975 200 - Sold (no pix);
1978 200 - Sold - http://www.pbase.com/hboy/redbaron
1979 300TD - Sold
http://www.pbase.com/hboy/greenwagon
http://www.geocities.com/hboy726/300TD.html
1985 230E - now my daily driver...

runs about 88-90 in the winter and 90-92 in the summer on the open road.

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Paul 1987 300 SDL; 2000 ML; '69 MGB; '68 VW Fastback

Runs just a hair above 80°C now in the winter and it ran in the mid to upper 80°'s during the summer.

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DJ


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

My E300 runs between 68-74 in the winter. Between 80-90 max during the summer. Do my winter reading seem a little low?

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#dieselFLEET
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'97 E300
'99 E300

My car has been running hot since I had my water pump go out a year ago... but in the winter I have noticed that it does tend to run a little cooler than in the Summer... In the Summer it tends to run a little under 100*C and right now it's at about 90*C...

My 240 will not go over 80 mark when it is in the teens or 20s.No matter how much or long the motor is on.
Of course the heater will not get as hot either. Any temp from about 30 degrees and up it will be on the normal 100 120 heat range. my 2 cents

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A couple of Ford pickups F 150,250, 350 missed.
1983 240 D 256,000 miles ,auto, ac.

How detrimental is it for the engine to not fully warm up to it's "normal" operating temperature? Is it better to be hotter than colder?

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#dieselFLEET
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'97 E300
'99 E300

Even if it's 10*f outside, my TD will always get up to 95-100*c when I go above 60mph and 7psi boost on the highway. Radiator fins are clean and straight, heater goes to 80*f when its hot and radiator hose is hot. Would "drilling holes" in the thermostat help coolant flow to get the temp down?