In one thread someone mentioned it should run close to 90. During the summer I run under 80, usually about 75-78. During winter, probably around 70 if that.

I never had good heat during the winter. On a recent all highway trip I checked my milage and its poor. About 16 all highway. And the engine temps never got very warm. Again around 70 or so. And I have no viscus fan right now!

So I put a piece of cardboard in front of the radiator. I now run just under 100 and my milage is about 18.5 and climbing as I average more fills.

So clearly my t-stat is bad. But I am also wondering what I should see temp wise when I replace it.

Just not looking forward to adjusting lambda AGAIN, this time at true operating temperature.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

Are you sure there is even a thermostat in there now? When I bought my SDL it would run hot in the city, too cool freeway... pulled the housing, there was no t-stat to be found.

The car had a bad fan clutch so the PO just pulled the stat as a halfassed fix. No shock really as the heater core was bypassed too for some reason.



Anyway, I have never had my cars run around 90°C constantly. Even during the hell we had last summer. They may creep into the upper 80s with the A/C on full load. NOW, I do have all cooling system updates available depending on the drivetrain. Late fans, different pulleys, new radiators, correct thermostat, etc.

You would be shocked how much cooler the car will run with simply a new radiator along with a clean A/C condenser.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Good point. Mine may be missing. My fan clutch was bad, but always engaged. Which is why I pulled it for winter. Plus I just wanted to hear the V8. Although I miss the whoosh sound of the fan spooling up.

Anyway. I ordered a t-stat today. Not cheap!!! I will probably have to put the viscus fan back in if this thing starts to run at the right temps.

I am just glad to get my fuel economy up!

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car

The car with everything running properly should run 85-90. Temps will creep up toward 100 on hot summer days (southern/southwest US climates) at long stoplights, with the A/C running. IMHO anything over 100-105 there is something wrong.

Normally it's a bad fan clutch. Also, make sure the radiator is clean and not full of debris, particularly toward the bottom front where you can't see if it's gummed up with crap. A properly operating, efficient cooling system with a good fan clutch should keep temps down at 95 and below, all the time and in most all conditions.

Anything BELOW the 80 mark also indicates an issue -- could be as simple as a bad gauge/temp sender, but could also indicate thermostat problems.

Cheers,
Gerry

Job done. Original t-stat was in place, must have been stuck open. Tomorrow will be the cold start test to see how fast she warms up now. But after she sat for a couple hours, she seemed to warm up much quicker than normal. And it held a temp of about 85 degrees at a very constant! Much better!

By the way, it helps to search better. The info I found said the t-stat was on the top of the water pump. Its not, its on the side really. Maybe top side to be exact. I figured it was under the housing that is home to the temperature sensors. Nope! I had to make a new gasket from scratch. Not happy.

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1991 560 SEL / 185k miles
1992 750il / 17k miles - project car