M104 Overheating - PeachParts Mercedes-Benz Forum

TROVERMAN · #1 06-15-2004, 08:34 AM

On hot days, or even not so hot days, the car will go to 100C. On really hot days 95F it will reach 110C. No higher so far. Not at all familiar with the cooling sys on this car (1995 E320 Wag) The coolant was the green stuff when bought and we changed it to MB Orange. No problems all winter, no overheat, great heat. Called MB about overheating prob and they said bring it in, way too complicated to do anything. Would like to fix myself. Appears to have new waterpump and radiator, thermostat new 2003. Here is what I have observed so far. After running for a few minutes the upper rad. hose is hot, lower one is not. The short one to the engine from pump is also hot. When temp hits about 90C, the lower hose gets hot. The twin elec fans seem to run slow all the time when the AC is on. Unplugging the 4-prong plug on the WP makes the fans run max. Sometimes turing on the heat makes temp drop almost 10-15C. Sometimes water level rises almost an inch in the tank when hot. Last night on a drive with outside temp 70F in no traffic the temp was at nearly 100C at a redlight. Cooled off when driven 35mph. Our Volvo temp guage goes to the middle and stays there. The MB guage is always moving around, making you nervous. Need help. Whats normal, what are some things to check. Recently I took a bunch of hoses off and reflushed all the coolant out to make sure no blockage. After that, I started seeing a little water on the driveway under pass fenderwell. Not alot, perfectly clear, and smells like water, not antifreeze. Where does the AC drain, by the way? Please help, will check back tomm morning. Thanks.
Oh by the way, what about the monovalave? When the heat is on, you can feel the aux WP on. How do you check the monovalve? With CC off, cooling hoses which go under batt box are cold, when on, they get hot. Should they always be hot?

zafarhayatkhan · #2 06-15-2004, 10:42 AM

What is your engine temperature at highway speeds? If it is around 85-90, then your basic cooling system is fine and either the main cooling fan or the Aux fans are causing the problem. 100 C is normal.

According to MB, temperatures approaching 120 C are no cause for concern. High speed Aux fans come on at 107 C. You can change the resistance of the temp sensor to start the high speed fans at around 100 C.

The temp needle in your MB is very sensitive, thats why it moves around. That is a good thing. Other makes have a range of engine temperatures for a single spot on the gage. So, instead of slowly going up in temperature, the needle jumps very quickly when the car overheats.

jcyuhn · #3 06-15-2004, 10:49 AM

Don't worry about the guage vs. your other cars. MB uses guages which tell the actual, current temperature of the engine. Many other makes use an "idiot guage" - it points at the same spot in the center of the range for any temperature from just above stone cold to just below boiling.

Your m104 isn't really overheating. That said, it does seem to be running warmer than most others under similar conditions.

How does running the a/c affect the temperature? It's quite normal for the dual fans to run when the a/c is on. Is the temperature lower and/or more consistent with the a/c running?

Does it largely heat up during stop & go, but cools down when moving? From your post I don't really understand what is happening.

A couple of very random ideas. Check the aux fans to be sure they are spinning the correct direction - the air should blow through the radiator. How is the fan clutch? It should be engaging when the engine reaches 100C, making for a very noticable roaring sound when accelerating away from a stop. Any idea on the condition of the waterpump? I've not heard of m104 pumps having problems with the impeller, but anything is possible, I suppose.

- JimY

suginami · #4 06-15-2004, 07:13 PM

Your car appears to running at exactly the temperatures at which it was designed to run.

dtf · #5 06-15-2004, 08:00 PM

Was it a Mercedes thermostat that got put in your car in 2003? Another cheap variable to eliminate is checking that too.

TROVERMAN · #6 06-16-2004, 08:00 AM

Thanks everyone for the replies. They are all very helpful, I am less concerned. When driving on the highway, say 50 mph or higher, air on or off, the temp is probably 87 degrees right on. The temp seems to only rise when idling in stop and go or just in park. Last night the temp was right at 100C and upon revving the engine you could definitely hear the main fan roaring. The only time I hear the aux fans on high is when I unplug the (fan) sensor on the water pump. How do you make them come on a little sooner? I think with the air on the temp is maybe 5C higher than with off. Actually, I think with the air off the car never goes higher than 95C. Last night with the temp at 100C, turning on the defrost button brought the temp to about 85C. The water pump and the thermostat are both new in 2/03. As for the water level in the tank, it is now about 1/2 inch over the line but is staying there, even when hot or totally cold. Thanks for all the replies again, I keep an eye on it and check back tommorow morning. It will be mid-to upper 80's this week.

zafarhayatkhan · #7 06-16-2004, 08:34 AM

Temperature around 87-90 at speeds above 20 mph and temperature as high as 105 C when stopped with AC on, indicates that the Aux Fans are not working properly.

The Aux fans maybe be turning but at a lower speed than required. Possible defective fans and/or pre-resistor.

JimF has instructions on how to start the aux fans at a lower temperature. He also sells a "cool harness.
http://pages.prodigy.net/jforgione/MB_S500.html

suginami · #8 06-16-2004, 05:41 PM

Quote:

Originally posted by zafarhayatkhan
Temperature around 87-90 at speeds above 20 mph and temperature as high as 105 C when stopped with AC on, indicates that the Aux Fans are not working properly.

At a constant cruising speed, I think it is normal for an M104 to run between 87-90.

If the temp is abouve 85 degrees and I'm in stop and go traffic or if I stop the car at a stop light after a run on the freeway, if I sit there long enough, my engine temp will steadily go up until the high speed fan kicks on at 107.

It is perfectly normal.

zafarhayatkhan · #9 06-16-2004, 09:30 PM

Suginami, I should have been clearer. At speeds above 20 mph, no fan is needed for cooling. If the temperature is around 87-90 at high way speeds, that indicates that the basic cooling system is working properly.

Now if the car is stopped with the AC running and the temperature starts to go up, that indicates that the aux fans are not providing sufficient air flow. In my car, the temperature approaches 100 C while stopped with AC on but does not reach it.

The only time it went above 100 C was when the aux fans were bad. They were rotating very slowly in slow speed mode and blowing the fuse as soon as I removed the temp sensor connector for high speed mode. After I replaced the aux fans and pre-resistor, temperature does not reach 100 C, with outside temperature around 85 C.

If in the future, it starts to go over 100 C, I will install the cool harness. It is a whole lot cheaper to replace the aux fans than all the electronic components and wiring in the engine. Mechanical parts like gaskets and engine blocks do not like the high temperatures either.

87-90 C seems to be the optimal temperature for this engine as evidenced by the highway operation. For some reason, MB was not willing to operate the aux fans at high speed for extended periods of time, one reason maybe extending the life of the fans and possible noise reduction.

In any case, the location of the aux fans is such that they are very susceptible to contamination and moisture from the road, reducing their service life.

I would like to add that MB considers temperatures approaching 120 C under certain conditions normal, but remember that the warranty runs out at 48K miles! Long before thermal cycle of heating and cooling have had a chance to degrade the components.

TROVERMAN · #10 06-17-2004, 08:20 AM

Last night the temp was about 75 degrees and the car was out on the interstate highway going about 75-80mph, and the a/c was on. However, it seemed to actually be running cool, at around 82-85C! Upon stopping, it went up to about 92C, and no more. For now, seems to be o.k. An older Audi 20V 5cyl turbo sped up upon attempting to pass. 80-100mph comes quite effortlessly with the m104.