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Old 03-30-2003, 07:45 PM
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Join Date: Feb 2003
Posts: 10
92 300SE running a little hot...

1992 300se (140) with 126,000 miles on her. The coolant needle is moving slowly from 80 degrees celsius to the 100 degree celsius mark. Very rarely have i seen it go over the 100 degree C mark, but it has done it, but never has overheated. I replaced the thermostat but it still occurrs. Nothing major really, i have owned this car since it had 104,000 (or last year) and it has always happened. I was just wondering if this is normal, or is it a cooling problem ( radiator- water pump- etc.) Any and all advise is greatly appreciated.

Gratzie and Thank You
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Old 03-30-2003, 08:28 PM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,010
I'll assume that your 103 engine is configured the same as my '88 190E 2.6.

The engine driven fan viscous clutch does not fully engage until about 100 C, so in heavy stop and go traffic or idling in warm weather the temp will often creep up to about 100. You can tell the fan clutch is fully engaged by revving the engine to about 3000. If it's fully engaged you should hear a distinct roar, and you can feel greatly increased air flow.

The electric fans have two speeds and are partially controlled by the A/C system, so if you have the A/C on, the fan(s) will operate intermittently based on the condenser cooling requirement. The engine will often operate cooler in stop and go traffic if the A/C is on.

With or without the A/C engaged, the fan(s) will activate at their highest speed at about 110C and they can be clearly heard.

You can check the fan functions by allowing the engine to idle on a warm to hot day while observing/listening for the fans as the coolant temperature rises, and you can do this test with the A/C both on and off to gain a full understanding of the fan control algorithms.

From your description, I wouldn't conclude that you have a problem, but verifying fan operation can give you some peace of mind.

As time passes deposits slowly build up in the radiator, which will reduce radiator efficiency and cause the fans to work harder, and eventually the radiator may become so inefficient from deposit buildup that overheating is inevitable. The best way to insure maximum life from the radiator is to change the coolant every two years using an organic inhibitor based antifreeze such as MB antifreeze or (GM) Dexcool. Conventional inorganic inhibitor antifreezes with silicates, phosphates and other salts will clog up aluminum radiators a lot faster than organic inhibitor based antifreezes.


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Old 03-30-2003, 11:42 PM
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Join Date: Mar 2003
Location: Southern California
Posts: 2,010
Viscous fan clutches key off the radiator exit air temperature, so the coolant temperature at full engagement is approximate and will vary between models. About 100 C is where I can hear it roar when the engine revs up on my '88 190E 2.6.

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