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400se Engine temp question

3175 Views 13 Replies 7 Participants Last post by  samosali
Hi , pardon if this has been brought up before.
My 92 400se seems to, at times, run on the hot side. My temp guage goes almost all the way to the white line before the red and then cools down to the line between the top and the 80 line. It goes up and down depending on traffic ,ambient temp etc... Is this normal? any advice will be greatly appreciated!! Kevin
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-thermostat replacement,
-coolant temperature sensor replacement,
-with proper coolant mixture
-upper engine wire harness replacement

the temperature gauge is between 80+ and 100 °C (next white line after 80 mark) in my car .... usually ... in winter and summer.

Of course in theory the temperature can go to 120 °C and more, and in practice it can also rise to that value if there are such circimstances (staying in traffic during summer, etc.). I strongly believe that (bayhas will get mad with me) the "normal" temperature during driving the car is not more than 100 °C (summer). Indeed there is a statement in manuals that temperature gauge can reach the red marking; let's say 120 - 125 °C, but this is the upper upper upper limit, which is far away from normal and it is allowed only in special situations according to MB manuals. So logically is: if MB allows 120 °C then 100 is not so bad, we can say, but 120 is really a limit, not a reference for normal everyday driving.

In addition, rapid fluctuations of temperature gauge are also not ok one should say ... they indicate at some malfunctions (thermostate, viscous fan ...).

This is also interesting:
I experienced fluctuations of temperature gauge pointer over 85 °C. When it reached that temperature it usually jumped to 100 and more ...and then slowly (sometimes) dropped to 80+. I noticed some logic in these fluctuations with driving regime so I accepted it as a normal. I also studied this forum and noticed that this should be normal. I let the air out of the cooling system, etc. However the temperature fluctuations in addition to relatively high temperatures were still on. I got an idea (read about it on some another forum) and I tapped on the cluster display where the temperature gauge is and I noticed that the pointer jumps according to my taps. So it was not related to temperature changes but to something mechanical.

Solution: I removed the cluster, I removed the module where the temperature gauge is and I cleaned all contacts with contact cleaner spray, I also opened and cleaned the connector with 4 wires which comes into the cluster from behind (square shaped connector, the first on the left side of the cluster in direction of driving). The problem solved, relatively high temperatures and their fluctuations dissapeared.

Conclusion is that your high temperatures are maybe a result of bad contacts related to temperature gauge or the wires to it. when the car will be hot, test the situation with tapping onto cluster display over temperature gauge. if it will jump then you've got it.
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Interesting. I wonder if its a newer vs. older kind of thing. Both my cars are '97 models and they both behave the same way. (Both have had new thermostats installed in the past year too.) The temp climbs to 80 within 2 or 3 miles and then stays about a needle's width of the 80 mark. With the AC on, it will move closer to the halfway point between 80 and 100. I have never seen either one go over 100 even in stop & go driving on a hot day.
So there is at least two of us with very similar cars in terms of coolant temperature :)

My goes up to 80-85, and stays there.. Almost 90% of the year.. Only very HOT summerdays can convince it to go up to 90 C
I would say that is an ideal behavior. I was told by a head of MB dealer here that it should be so (80+ for cold days, 90 for summer or with trailer etc. Of course this is valid for driving conditions, not for staying in city traffic during summer). I assume it needs only several minutes to reach 80.
Well ,I am going to replace the thermostat and start from there. To do a general one post response to most of the questions... I have the correct mixture of coolant , replaced the coolant cap , the fans seem to come on, according to my mechanic, at the proper time . It only goes back down to 80 going either down hill or after crusing w/o slowing for a few minutes. I did try the tapping on the cluster and it doesnt jump around. I will also look at the coolant temp sensor.
I read the owners manual and I agree that while it states it can get that hot ,I can smell it getting hot and that worries me, I LOVE(LOL) this car even more than my Sliver Spirit .
Most probably the new thermostat will solve the problem. Good to have replaced the radiator cap. Most of people do not know that it is crucial to the cooling system (it maintains the correct pressure). Good for you that temp gauge is not sensitive to tapping (no need to remove the cluster ...).

You have three coolant temp sensors, that one with one pin is for temp gauge in the cluster. that one with two pins is for AC (external fans), and that one with four pins is for an engine computer. all of them measure the same media (coolant).
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