Wow, lots of people chasing a problem that is not really a problem.

#1: I don't believe the temp gauge is really precise. As long as mine reads somewhere in between 85 and 105 C I do not worry about it.

#2: I cannot think of anything wrong with the car running at 95C all the time. In fact that is a good operating temp. It's not good to consistently run the motor cool, and it's obviously bad to run it hot.

A properly operating thermostat will keep the operating temperature relatively steady. I've had many cars, any many Mercedes and when you see the temp gauge moving around under normal operating conditions something isn't right. The only time the temperature should fall below normal is if you happen to switch the heat on while the car is at or near idle...otherwise it really should operate within a couple of degrees of the design temp.

The MB stat I removed would spike over 100C and drop to under 80 during routine running...that's just wrong. The new Wahler behaves normally, the car warms up and the temp stays steady. These gauges are pretty accurate if they're working right, and this one is.

A car which runs at 90C+ is above its design temp. When new, these cars ran at just above 80C...a car running at 95C-105C means either the gauge is wrong or the engine is running warm. 80-85C is not cool...it's normal for these.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz

Very true. I just often don't believe that the car is running at the temperature displayed on the gauge. My car is 25 years old and has a quarter of a million miles on it. There is a long list of things that are no longer within design specs. When mine says 90C, it might truly be running at 80, or 85, or 95. The only way to tell for sure is to use an infrared heat gun. I find that it's splitting hairs for me to worry about the gauge reading as long as it's relatively normal (i.e. not 60C and not 115C.)

As far as your wild fluctuations in temperature, agreed, that was most definitely not normal!

The SD has a brand new OE thermostat........Wahler.

It runs at 82-85C. when it's below 2000 rpm with a light load.

It runs at 90C. when at 2800 rpm at highway speeds.

It runs at 95-98C. when at highway speeds at maximum power (held for more than 30 seconds). It very slowly returns toward 90C. after 10-15 minutes.

I've checked the cylinder head and confirm that the head runs about 7C. cooler than the gauge.


Therefore, don't draw any firm conclusions on the capability of a 617 to maintain a perfect temperature under all conditions.

The 606 may be different.

Brian,

I may be missing the point, but your SD does not sound as if it is controlling temp appropriately. While I can understand some increase in temp under heavy load, with appropriate air flow at speed the transfer should offset the increased heat load.

Something isn't right ... or, am I missing the point?

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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg

Well, it has a brand new water pump, a brand new thermostat, it behaves in an identical manner whether the ambient temp is 0F. or 95F...........so, if it's not behaving properly, I'm willing to listen to all rational ideas..........

You can't condemn the radiator if the performance is identical at 0F. It's the only item in the system that is "aged".

Hmmm - was the temp maintained in the same manner prior to all the replacements? Prior to the new tstat?

__________________
George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg

It was absolutely identical with the old stat.

However, it has changed behavior over the course of the last eight months or so. Previously, it would very rarely climb above 90C. The ambient would have to be very high. Now, it climbs to 95C. just about every day..........