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Old 12-01-2000, 01:48 AM
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Hey guys, I have an 89 300E. On my way to school today (about 5 miles each way) I noticed the temp guage climbing, especially at slower speeds or while at stop lights. However, while driving at continous speeds around 55 mph it is fine. I checked the coolant level and it was ok. I am in Daytona Beach so the temps are very mild (around 65 F), and neither the A/C nor the heater were in use. Additionaly I recently replaced the fan clutch, so that is hopefully not the culprit. I can only assume it must simply be the thermostat. At least I hope it's that simple. Anyone have any ideas?

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Old 12-01-2000, 02:23 AM
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Join Date: Apr 2000
Posts: 412
I had the same problem with my 1990 190E 2.6 and indeed the problem was the thermostat. The thermostat would open just a crack and would be ok on the highway but in traffic the tempature shot up quick, even here in Chicago. The thermostat should be about $25 and takes about 3 minutes to replace. Three bolts and a rubber O-ring. You can remove the thermostat and check it very easily.
I would also check the electric cooling fans to make sure they are functioning. The should be coming on when the tempature goes up, if not, the most likely cause would be the relay. Just to mention one of my fans was also wired improperly and was blowing in the opposite direction of the other. Re-wiring the harness corrected the problem.
Good luck.
1990 190E 2.6
1996 Grand Voyager 3.3
1985 Mustang GT 5.0 5 SPD
1982 Suzuki GS 750T
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Old 12-01-2000, 03:18 AM
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Join Date: Sep 2000
Location: Sherman Oaks, CA
Posts: 4,749
its either the thermostat or the water pump, I think it could be the thermostat, but sometimes the water pump can itself pump less at slower speeds and more at speeed and can also cause those symptons.

When I've had thermostats need replacing, the car would run hotter but not drop or raise up at least not to my knowledge, of course when going faster, the air also helps to cool it.

Either way, get it looked at by someone who knows about cooling systems and knows mercedes. You don't want to overheat the engine and end up with an expensive repair job.

I'm not a tech, but this is what I know from my experience with cars and temperature problems. hehe

'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon
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Old 12-01-2000, 10:54 AM
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Join Date: Aug 2000
Location: Houston, Texas
Posts: 333

What could go wrong with the water pump to cause an engine to overheat other than the water pump leaking out antifreeze. The pump vanes are metal. Do they wear out?
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Old 12-01-2000, 01:25 PM
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Join Date: Nov 2000
Location: Long Island, New York
Posts: 79

I have a 89 300SE and had a similar problem. A thermostat replacement cured the problem and will likely do the same for you. In the off chance that a new thermostat doesn't take care of the problem take a look at the radiator in addition to the water pump.

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Old 12-04-2000, 08:11 PM
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Thanks fellas,
I swapped out the thermostat (old one was in real rough shape) and for $22.50 the problem was solved.
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Old 12-04-2000, 08:33 PM
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Join Date: Jun 1999
Location: Los Angeles, Calif, USA
Posts: 521
Other than the water pump leaking out antifreeze, the pump vanes may disengage from the shaft turning freely.


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