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.

A) Test your cooling system pressure cap. It should not leak down and should release pressure above 17psi.

B) Install your new thermostat.

C) Test the fan clutch operation. You should hear it roaring when accelerating from a dead stop when the engine temp has climbed up around 105c.

D) If you suspect the fan clutch is not working turn the engine off and measure the radiator temp with your hand or some temp measuring device. The most crucial part is the core near the cooling fan. If its cool to the touch then the radiator is stopped up inside.

E) Make sure the fins are not stopped up with debris.

Well I need to let everyone know what's happened so far (pardon the length). I'd like to close the thread at this point by saying everything is back to normal, but I don't think that's the case just yet.

I have been driving the 300E (keeping a close eye on temp)while waiting on my new thermostat to arrive. Careful driving has kept the temp down and everything has been ok, but my luck ran out last Wednesday evening.

I had stopped at an ATM for cash when suddenly there was a loud pop and an explosion of steam from under the hood. Temp had been a little high, but not bad because I had just stopped. I quickly shut the car off and pushed it off to the side to try and determine what had happened -- all the while praying for a busted hose. No such luck. I had a five inch split in the radiator below the upper outlet in the plastic side piece. Why didn't I order that radiator too!! Now I'm wondering if I've damaged the car.

Well, I got the car home and read everything in the forum on radiators. Even with the help of the forum's past radiator topics, I still couldn't decide what to get, Behr or Nissen. I was just plain sick with what had happened to the car anyway, so I put the decision off until Thursday.

Thursday I decided on the Nissen (taking Fastlane Phil's advice), and place my order (I've covered this under another post). I received and replaced the radiator and thermostat yesterday, flushed, and added 50/50 Prestone antifreeze. By the way, this stuff is called Prestone 5/150 Extended Life; and is silicate and phosphate fee; and meets DaimlerChrysler MS7170, MS9769 (whatever that means); and it's orange!!!

After a couple of short test drives around the block, I drove the car hard for an hour or so yesterday evening. While on the highway, temp stays around 87C. When stopped, temp stays low for a couple of minutes then slowly starts to creep up. When it gets just above the unmarked line between 80C and 120C on the gauge (what is the marking anyway? Does anyone know?), I hear the auxiliary fans kick on. The temp temp then slowly falls back down to close to the same as it is when running on the highway. Sounds normal? I think so from what I've heard here and from what my owner's manual states -- I really hate to see such wide swings though. Maybe I'm just gun shy now, and I really hadn't paid a lot of attention to how the cooling system acted until I had this overheating thing.

Anyway, there's more. I figured I still needed to test for proper operation of the aux fans, just for piece of mind. I popped the hood this morning to install an new pressure cap on the coolant reservoir (also for piece of mind), and for some reason decided to look at the fuses. When I removed the cover the first thing I noticed was that the card that tells what's what on the box cover was charred! The fuse in position "D" was the culprit. It looked like maybe the element had cracked but still made contact intermittently (causing heat). I dunno. I checked what I could read of the card (does anyone know if I can buy the card as it is ruined?) and saw that fuse "D" is the auxiliary fan!

So anyway, that's where I am now. I haven't replaced the fuse yet and I need to check some things I suppose. Any advice guys?

Ken Fuller
1990 300E (parked again)
145K Miles

Well I replaced the aux fuse and warmed the car up. The aux fans are acting differently now. With the ac on, both aux fans come on low speed with only a little rise above normal operating temp. I took it out on the highway and ran it a little. Brought it back home and watched it at idle some more. It's about 80F outside and now the needle on the temp gauge is not moving much above the 85C mark. Before, even after I replaced the radiator, coolant, and thermostat, the temp was going above the unmarked white line between 85 and 120 before the aux fans kicked in. Now, even after idling a while, the temp is staying pretty constant, with the aux fans cycling on and off early.

I guess the aux fuse really was intermittent -- to the point that the fans weren't able to kick on early in the temp rise. Anyway, I think it's now fixed. I hope this someone with similar problems.

Ken Fuller
1990 300E
145K miles

. . . clear report
 

Ken,

Appears to be 'gold' star time! I would say you've fixed it. Everything you say appears as it should be from what I've experienced.

When it gets just above the unmarked line between 80C and 120C on the gauge (what is the marking anyway? That
line is 100C or 212F. If you car stays there, then it is perfectly 'safe'.

Ken,

To repair/refurbish/replace your fuse map go to

http://www.peachparts.com/shopforum/tech-help/18259-86-300e-fuse-box.html

JCE had posted a copy of his card from the 300E, although an '87, the cards should be close to the same.

Hope this helps.

Thanks Mike and Jim. I've got my fingers crossed but everything has been fine all day. I think the major problem all along was the fuse. I'm an electronics guy by trade, but before I got this car I would have never suspected an intermitant fuse (this will be the second I've had). I suspect that the fuse was high resistance where it had broken. That is why the low speed never came on with the ac (not enough juice), but the high speed came on at high temp. I'll check out the link for my new fuse card.

Ken Fuller
1990 300E (on the road again)
145K miles