I noticed both aux fans running full tilt the other day when I got home. I glanced at the temp needle and saw that it was only a little ways from the red (it was only 85F outside). So I kept an eye on it for the rest of the week until I could take a look this weekend. It continued to run very hot when stopped in traffic, but not all the way into the red. Well, I was thinking water pump replacement, but after a search, it sounded more like the thermostat. So, I took it out and checked it in boiling water. It barely opened when hot. I ordered the thermostat and o-ring from fastlane and stuck the thermostat housing back on without the thermostat. This should keep it cool until I get the part in right?? Well...its better, but when stopped in traffic it's still getting awfully hot. Why would this be? I would think that without a thermostat, the car should almost run too cool. Am I missing something? The fluid doesn't look contaminated. Am I still going to need a water pump? Does running too hot do something to the antifreeze and now it needs replacing (it was changed a year ago)?

Ken Fuller
1990 300E
145K Miles

Pull out the radiator and clean out radiator using a power washer or compressed air. That helped my car alot and cured it from a mild overheating problem... Also even if it is not the problem it definately could not hurt your cause.

good luck

bob

If your car is a '90 and the radiator has never been replaced, you may want to do so...your car has a notable tendency to have its radiator fail catastrophically. Not to make you paranoid, but more often then any of us would like to admit the 300E radiator top necks fail-if you were to not notice the huge water loss and attendant temp increase, you could cook the motor. I just pro-actively replaced my 300TE-I figured the old one had gone 170k mi and 13 years, so that was long enough: plastic gets brittle.

As to your case, it might not be a poor performing radiator; I know sometimes that a lack of a thermostat allows the coolant to flow through the radiator too quickly to cool properly, so perhaps that's why you still experienced elevated temps?

Good luck, and keep us posted.

Might be a weak fan clutch causing the temp to rise, while in stop and go traffic.

Thanks for the input MarkL. Do you think that that is something that I should be able to see easily? Or test for? I thought that the fan clutch was supposed to slip somewhat until about 2000 rpm.

Ken Fuller
1990 300E
145K Miles

You may want to check your a/f ratio concentration.
If this has just been noticed with the warmer
weather, it is possible that when you had the a/f changed, it is too concentrated. 50/50 or less, depending on climate, is best. Richer will cause your condition.

If it comes down with the aux. fans, then the radiator, fans, etc are funtioning.
Just an often overlooked check.

Thanks Arthur. Actually it doesn't come down when the auxiliary fans kick in. It stays low, around 80C (remember, thermostat removed)when on the highway. When I'm stopped in traffic it immediately starts to rise. The aux fans kick in at some point, but the temp doesn't drop back down. If I put the car in neutral and rev the engine to 1500-2000 rpm, the temp then starts to drops.

Ken Fuller
1990 300E
145K miles

Make sure you main fan is clutching properly. You should be able to hear it kicking in. If not, then the clutch is shot and will need to be replaced. If the main fan is working, I would replace the radiator. Hell, replace it anyway. You will notice the difference.

Ken,

These cars can't work without a thermostat. The thermostat is designed to close one side as the other opens. If you take out thermostat both sides are open and you have bad circulation. Actually, I'm surprised it's not overheating. Wait for your new thermostat, it should take care of the problem.

Another thing to check to make sure everything works normally is the aux fan half speed. Does the half speed ever turn on while the AC is running? If not, bridge the two wires that go to the high temp switch on AC drier. If it turns on now keep the wires bridged until the next AC service and then change the switch. If they still don't turn on check the big resistor next to the AC drier. Might be burned, change it.

Vinamg

[Edited by vinamg on 06-27-2001 at 12:28 AM]

Well thanks everyone. I guess I just need to relax and wait till the part comes in. I'll let everyone know the outcome.

Ken Fuller
1990 300E
145K Miles

Ken,
I have the same damn problem in my 92 190E 2.6 with 97K on it. When the car is moving the temp is fine and when it stops the temp goes up. When I put it in neutral and revup the engine the temp comes back down. Guess what ? I put a new thermostat, new fan clutch and flushed the radiator with a garden hose at home. It still does the same thing. The auxiliary fan seems to kick in at the right temp. Regardless of the fan coming, the temp does not come down until I revvup the engine or until the car is moving again. So temporarily, I added water wetter (Redline) and it seems to help, atleast it keeps the temp below 105-110 in stop & go traffic. I am thinking either there is a blockage in the radiator or the waterpump is faulty. I am kinda stumped because the waterpump does not leak. Anyway this is my 10c worth and hope this helps you.
Regards,
smk_texas
92 190e 2.6 97K

The waterpump usually either works or doesn't. Most of these problems are related to poor circulation in the radiator and partially opening thermostats. If the pump is quiet and not leaking, I would look elsewhere. BTW, flushing with a garden hose will not remove scale or sludge in the core unless you have a lot of pressure and flow. It may seem the flow is adequate, but the real problem is heat transfer not necessarily flow. Actually more heat is transferred at lower flow rates all other things being equal.

Add more coolant if you can. You might be borderline low, where the low level coolant light won't come on. Or the coolant sensor could be busted even.

Good luck

Paul

. . . . maybe that's the problem?
 

Arthur's suggestion need to be stressed. A story best does that. Two days ago, while at my tech's shop, a customer drove in and complained about high temp, etc. We all know the story!

I asked about his 'coolant' mixture ratio. He said ". . I just changed it so it's new and it sb ok". Let's check it.

The handy-dandy Prestone AF tester "pegged" itself to the top! Thus Arthur's point, check your mixture. His was 80/20 and the 80% wasn't water!!!! Nuff said!

Prestone PN is AF1420P. $2.89 at AutoZone.
http://pages.prodigy.net/jforgione/AF_tstr.jpg

Overheating no no no thermostat
 

MBZ are designed such that the thermostat opens the passage to the radiator AND closes the recirculation passage at the same time. Without the thermostat to block the recirculation passage there is very litte pressure to force coolant through the radiator and they will surely overheat.

Also, often old 'green' antifreeze begins to react with minerals in the water and the aluminum to form insoluble hard deposits in the radiator tubes. these have to be mechanically removed by 'rodbing it out.' Never use anything but MBZ antifreeze or the Orange stuff. Regular green stuff leaves those deposits when th eanit-corrosion additives give up the ghost.