1995 S500 W140 Running Hot - PeachParts Mercedes-Benz Forum

HG95S500 · #1 04-02-2006, 11:24 PM

Hello -

I have 1995 S500 with 106,000 miles. Just recently I noticed that the engine was running hotter than normal. Specifically, the temperature gage would rise up to 100C and even past 100C. This is without the AC running. Also the temperature would not go down rapidly even at highway speeds at an ambient temperature of 60F. In the past high rpm driving would reduce coolant temperatures. As a point of reference the engine used to run normally between the 80C and 100C mark only surpassing the 100C on the hottest days with the AC on. As a first guess I changed the thermostat with a new MB thermostat. Unfortunately, there was no change in the operating characteristics. It still runs hot even with a new MB thermostat.

Here are some more facts which I hope will help shed some light:

Water pump is not leaking (Water pump is original)
Radiator cap is original
Coolant level is good
Heater works fine
Coolant mixture is good with proper MB coolant
MB Thermostat is new and working
There is no evidence of coolant in the oil
There is no evidence of oil in the coolant
Engine runs fine overall

Last question - I assume a water pump is only bad if it is leaking through the weep hole to the outside, correct?

Thank you in advance for your help.

Regards.

Hynek

86560SEL · #2 04-03-2006, 12:09 AM

I hope you can figure it out. I have a similar issue with my 85' 380. If the outside temperature is above 70*F, and I am in town, it will go a little above what I am assuming is 100*C. When I get on the highway however, it lowers back down to a little about 80*C. In the winter, when it is below 45*F and I am on the highway, it goes down to about 55*C-60*C and never goes above 80*C, even in town. It really depends upon the outside temperature on how my reading is.

I have only owned this car since December and the warmest days we have had so far have been the lower 80s, so when summertime temperatures reach into the 90s, I am really going to be interested to see what happens then. I think it may be my clutch fan not working properly, but sometimes I can hear it roaring, but not when the needle is above 100*C. I think it may be the thermostat stuck open?

Good luck with yours!

A. Rosich · #3 04-03-2006, 12:23 AM

This may not be at all related to your problem but it would help you to try:

The twin electric fans at the front would come on (with or WITHOUT the A/C) to keep the engine temperature at check.

Those fans have a five stage (if I remember correctly) speed setting that will eventually come on as the engine temperature rises (for any given reason).

When you check the OBDII codes (on my car, I think your 1995 has an OBD-I) with the computer, there is a procedure to test the five settings (or speeds) of the electric fans.

If any of the speeds is not working properly, it will pop a failure code. If you have a failure on the lower speeds of the fans, they will not come on to lower your engine speed unless it is really hot (+110°C).

Here it tends to be hot and humid in certain places and the twin electric fans work at their lowest speed setting (very silent, you have to check them from outside the car to hear them) most of the time.

Now, what puzzles me is that at highway speed your temperature will not lower ??? If you find out your problem, please don't forget to post your solution.

pcmaher · #4 04-03-2006, 08:22 AM

My problem was the viscous fan clutch. I wrote up some details on my web page. This link may be helpful...

http://v12uberalles.com/fan_clutch.htm

JimF · #5 04-03-2006, 12:22 PM

Quote:

Originally Posted by HG95S500

I have 1995 S500 with 106,000 miles. ere are some more facts which I hope will help shed some light:

Water pump is not leaking (Water pump is original)
Radiator cap is original <-- time to replace
Coolant level is good
Heater works fine
Coolant mixture is good with proper MB coolant <-- Check out Menu#17

MB Thermostat is new and working
There is no evidence of coolant in the oil
There is no evidence of oil in the coolant
Engine runs fine overall
Thank you in advance for your help.

Regards.
Hynek[/QUOTE]
Recommend that you replace the "cap" since it's definitely is time! And I check the af/w ratio as shown in MENU#17. Odds are that the actual af/w ratio is 60+% for af. . . and that's not good for keeping engine temperature down. The only way you will know is to "test" it as shown in Menu#17.

If you want to turn the Aux Fans at a lower temp, check out MENU#18. Sort of like a do-it-yourself "Cool Harness".

If your VFC is 'bad', (if it's original, then is probably is), you can purchase a new one . . . or modify it as shown in MENU#20. You can also re-fill it; there's threads here on MSF that detail the how-to-do-it.

Well, that ought to keep you busy!

The Workshop MB · #6 04-03-2006, 01:31 PM

I have seen this problem before while working at the dealer. With everything working as it should, we found that the radiator was at fault. If you have accesss to a tempature gun, check the tempature across the radiator. Indicator is when the car does not cool down even at freeway speeds (more air is coming over the radiator). Here is a test to see if your fan clutch is working normally: Set a high idle for a peroid of time, you should hear a large blowing sound, that is your fan working.

In short, we ended up swapping in a new radiator (relatively easy replacement), vehicle ran at normal from then on.