Overheating - PeachParts Mercedes-Benz Forum

sokoloff · #1 01-24-2018, 06:54 PM

Yesterday I was stuck in a slow moving parade out of a parking garage. Was hardly moving for about 45 minutes. Had the car in Drive the whole time with the AC on. After about 25 minutes or so I noticed that my temperature gauge had hit the 120 mark. It wasn't quite to the red line, but it was darn close. I immediately turned on the heat, hoping to get some cool coolant flowing through the system. That seemed to work as the temp slowly came down to about 100. Then on my three hour drive home, the temp dropped to its usual 75 to 80 degree number.

All seemed well, but is there any chance some damage was done and is there anything I should check?

This is my E300D BTW.

Diseasel300 · #2 01-24-2018, 06:56 PM

Fan clutch and/or thermostat.

Dubyagee · #3 01-24-2018, 07:00 PM

Quote:

Originally Posted by Diseasel300

Fan clutch and/or thermostat.

Yep. A flow problem. Air or coolant. Simple thing would be to rinse out the fins of the radiator of dirt, debris.

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sokoloff · #4 01-24-2018, 07:12 PM

Wow, quick replies - thanks guys.

Thermostat was replaced seven years and 70K miles ago. Original and replacement are both 80 degree thermostats. Coolant done every three years with GO5 or Mercedes coolant. Have to check the radiator fins, but I would be very surprised if they weren't pretty squeaky clean.

Might not be a bad idea to replace the thermostat. How do I check the fan clutch? This is the first time in the 17 years I've owned the car that I've had an issue like this.

Does the fact that things cooled down and got back to normal after turning on the heat and doing the drive home tell me that anything is definitely good or bad?

dkr · #5 01-24-2018, 07:20 PM

My new thermostat got flaky after about 40K miles. Unfortunately, with the quality of new parts these days, putting a new part in recently doesn't mean it will stay working.

Dkr.

Mxfrank · #6 01-24-2018, 07:21 PM

Did the electric aux fan come on?

sokoloff · #7 01-24-2018, 07:48 PM

Quote:

Originally Posted by Mxfrank

Did the electric aux fan come on?

Have no idea. Is there a way to test it?

tjts1 · #8 01-24-2018, 08:00 PM

Common problem. The viscous clutch fan can't keep up with the cooling needs of these engines at low speeds. A new viscous clutch won't fix this because the fan is limited by the engine speed.

Diseasel300 · #9 01-24-2018, 08:12 PM

Quote:

Originally Posted by tjts1

Common problem. The viscous clutch fan can't keep up with the cooling needs of these engines at low speeds. A new viscous clutch won't fix this because the fan is limited by the engine speed.

Sure seems to work for everyone else.

tjts1 · #10 01-24-2018, 08:18 PM

Quote:

Originally Posted by Diseasel300

Sure seems to work for everyone else.

Yeah it works so great that this question comes up dozens of times every spring on the 124 forums. People replace the viscous clutch and the problem comes up again. Then some genius tells "Oh well you need to replace the radiator", they do that and then they come back again. "Oh well how old is your water pump blah blah blah".

The viscous clutch fan on the inline 6 powered W124s is undersized. Look at the 4 or 5 cylinder W124. These cars use a viscous fan with much wider blades because theres more room for the fan. The inline 6 doesn't leave enough room between the engine and the radiator for a properly sized viscous clutch fan.
http://www.benzworld.org/forums/search.php?searchid=25474937

Diseasel300 · #11 01-24-2018, 08:51 PM

Quote:

Originally Posted by tjts1

Yeah it works so great that this question comes up dozens of times every spring on the 124 forums. People replace the viscous clutch and the problem comes up again. Then some genius tells "Oh well you need to replace the radiator", they do that and then they come back again. "Oh well how old is your water pump blah blah blah".

The viscous clutch fan on the inline 6 powered W124s is undersized. Look at the 4 or 5 cylinder W124. These cars use a viscous fan with much wider blades because theres more room for the fan. The inline 6 doesn't leave enough room between the engine and the radiator for a properly sized viscous clutch fan.
Mercedes-Benz Forum

That's great, so explain how so many folks have the viscous clutch fans on the 6 cylinders WITHOUT overheating problems?

If the engine cooling system is healthy (and that includes internal cooling passages), the stock cooling system should keep up, especially in the winter time and in cooler climates.

If the OP wasn't having overheating issues previously, use common sense and fix what broke.

CDTurbo001 · #12 01-24-2018, 09:42 PM

With those symptoms I'd first check the fan clutch. If the air coming out from around the fan shroud is good and warm but the fan is mostly coasting on the shaft, it's bad. Could also be general crud in the cooling system but seems unlikely with your regular coolant flushes.

That's about the most gentle way to overheat an engine - got warm slow, didn't shut off and heat soak or rapidly cool, and got cooled down gradually and completely. If any damage was done it's only because said component was on the brink anyway.

treetops · #13 01-24-2018, 09:48 PM

Easy test for the fan clutch is to see how it behaves when you shut off the engine. have a helper shut off the engine and if the fan comes to a dead stop right away its probably good. If it freewheels to a stop its on its way out and should be replaced. That test and a new clutch solved my higher temp problem.

A new radiator can also be an option. I had to replace mine last year and never put the fan back on. Ran fine from Feb 2017 to today and its still off. Not that I recommend that for anyone, but the new clean and free flowing radiator seems to handle all ranges of ambient temps even with the AC on.

If youre going to replace the fan better get the proper allen tool, i.e. allen bit on a long metal shaft, other wise prepare to fight getting the fan bolt loose and out. There another tool to lock the water pump pulley. Not hard just there aint much room in between the radiator and fan clutch. BTDT on my 87 300TDT recently. Lots if how to's on this one

Mxfrank · #14 01-24-2018, 10:01 PM

The electric fan is triggered by two conditions:

Low speed comes on when the a/c high side pressure exceeds about 300psi.

High speed comes on at between 100-105C depending on the engine. At high speed, there should be more than enough airflow to keep the engine cool regardless of whether the clutch fan is working correctly.

You can jumper around the low pressure switch to see if the fan is functional, but that wouldn't tell you whether the switch was working. Same for the high speed switch.

One thing you should probably do is to check the low speed fan resistor, which is a white ceramic box on the left inner fender. These resistors often fail.

torsionbar · #15 01-24-2018, 11:25 PM

I'm surprised no one has mentioned the fan belt? Your w210 has two aux radiator fans triggered by the A/C. One electrically driven, and a second fan that is driven by the first fan via a small rubber belt. If you lose the belt, you lose the 2nd fan. It's easy to test - with the car off, spin one fan, and the other should spin as well.