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Old 05-25-2001, 02:36 AM
Snow bum
Join Date: Jan 2001
Location: Here and there . . .
Posts: 238
I think I am going to go crazy. My 300D had been running much hotter than I would have preferred, as the radiator was plugged. I was going to flush it, but one day last week it just decided to start leaking. I freaked out and had it replaced, as I did not have time to do it myself. I had been planning on replacing it myself, and I had even found a radiator for about $300, but I just couldn't wait for my car and I didn't have time to do the work.

Anyways, now I am $600 poorer, and although my car cools off much quicker than it used to, it still heats up when I don't think it should. The problem may be that I am not sure how my car should behave, but I have not driven another W124 that behaves quite like mine.

When I drive at or below 60 F (outside temp), the engine temp will hover around 85-90 C. When the outside temp is 73 F or greater the engine temp is at least 85 C, but often as high as 95 C. Here is the problem. Whenever I put any sort of demand on the engine, like driving up even a very moderate hill with the A/C on, the temp will often rise to 95 or 100 C. Today it managed to climb to just above 100 C while I was accelerating onto the highway, with the A/C turned off!! The outside temperature was only 76 F.

What do I need to do? I don't have money to keep throwing at the car, but I am willing to spend what it takes to get it to run properly. This is seriously causing me a great deal of stress. I commute at least 90 miles per day, and every one of those miles is spent worrying about not overheating my car. Any suggestions?

The MBs:
1976 300D (W115) - 330K and still going (sort of)
1991 300D 2.5 Turbo - Sold at 221K
1983 280SEL - Sold at 206K
1981 300SD - Sold at 232K
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Old 05-25-2001, 05:02 AM
Ashman's Avatar
Service Advisor
Join Date: Sep 2000
Location: Sherman Oaks, CA
Posts: 4,748
Well I would check your thermostat. It might be stuck in a more closed position that is restricting proper water flow.

usually when I redo a cooling system in a car, whether I change the radiator, water pump, or just the coolant, I usually go for a thermostat change if its running hot.

You could remove yours and put it in some boiling water I believe, and see if ti opens fully or not. ITs not hard to replace the thermostat, and I'm sure it is not that expensive at all on this site, with the gasket and sealant if necessary.

If its not the thermostat, you should make sure your fans are coming on, as it might be the sensor for the electric fan, that tells the fans to turn on at a certain temp.

If the fans are ok and thermostat is ok, then maybe the only thing left would be the water pump, or maybe the fan clutch for the engine fan if your car is so equipped.

So far my car has yet to break the 90* mark with AC on full in the sun at about 85-100 degrees outside. (varies with where I have been the last few days. )

I remember when my jeep would run hot, I took it to the jeep dealer, they replaced my water resevoir. I told them change the thermostat, they didn't. I took the car back still running hot. I told them to change the thermostat. They did not want to, I literally had to force them to change it, they kept saying it can't be the thermostat.

Well to make a long story short, the thermostat was changed, and the car has not run hot for the last 3 years, and I never went to that dealer again.

So I am thinking that might be your best bet.

'92 300CE - Sold
2004 C240 - C7 Wheels
2015 ML350 - P1, Pano, Ash poplar wood, Sport Dinamica interior, Running Boards Keyless go.
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Old 05-25-2001, 11:41 AM
MikeTangas's Avatar
Senior Member
Join Date: Apr 2000
Location: So. Cal
Posts: 4,430

If the T-stat wasn't changed when they did the radiator, change it if only for GP (should be simple - 3 10mm bolts, one o-ring and the T-stat. No sealant or gasket to mess with).

I also just read in your other post that you went with 50/50 mix. I did too and had a little warming up issue too. Drop the mix to 70/30 (H20/AF) and I think you'll see a difference.

I'm not sure how much volume your cooling system has, on mine it's about 3.5 gallons. I drained off 1 gallon of mix and replaced it with bottled water.
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

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Old 05-25-2001, 11:59 AM
Registered User
Join Date: May 1999
Location: New Location: VA Palo Alto HEALTH CARE SERVICES
Posts: 109
Ben, ..will you consider performing acid (citric) cleaning your cooling system. There could be a lot of scale build that hinders proper heat transfer. That's the primary cause of radiator failure, ..and as recommended, ...change T-stat to an 85 degree set point. Hope this helps.....Dont forget to properly bleed the water jacket.
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Old 05-25-2001, 01:09 PM
BENZ-LGB's Avatar
Strong, silent type
Join Date: Apr 2001
Location: Southern California
Posts: 1,663

Have you noticed a loss of power associated with your overheating issue? If yes, then check the head gasket or the valve adjustment. My old 84 300SD began overheating and the same time I noticed a loss of power. All the cooling system components checked out OK. It turned out to be the head gasket was leaking and thevalves needed adjustment.
Current Benzes

1989 300TE "Alice"
1990 300CE "Sam Spade"
1991 300CE "Beowulf" RIP (06.1991 - 10.10.2007)
1998 E320 "Orson"
2002 C320 Wagon "Molly Fox"

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Old 05-25-2001, 01:32 PM
The Bob
Posts: n/a

i just bought a 300d and it runs just as your does. the thermostat was replaced earlier this year and it is not loosing any coolant... i think as long as it does not run hot there shouldn't be much to worry about. This may just be the nature of the beast.

good luck
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Old 05-28-2001, 02:53 PM
MBenzNL's Avatar
Join Date: Jan 2001
Location: the Netherlands
Posts: 1,417
If you are really worried about the engine temperature, you can always shortcut the auxiliary fans so that they run 24/7...
Since my dash cluster doesn't support the temperature controlled auxiliary fans for the airco I retrofitted in my car and I am in the progress of getting the 96 C36 AMG dash cluster functioning in my 93 C250D, my auxiliary fans run constantly during the summer (AC on) and never run in the winter (I remove the fuse).
I don't like this situation that much, but the temperature is very constant whether I am driving or standing, whether the car is cooling or heating the interior...

Did you already receive the license plate frame?

1990 300SL-24
1993 C250D
with a minor 600+k kilometer
(the Netherlands)
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