W203 Coolent malfunction - Mercedes-Benz Forum

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post #1 of 5 (permalink) Old 10-31-2008, 11:09 AM Thread Starter
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W203 Coolent malfunction

So, My C Class W203 (2003) has just started having a small problem - Cooling fan starts cycling on-off as car warms up (temp guage shows 40) then when at running temprature fan on full blast but temprature low 40 - because fan on. - at this point 'Coolant malfunction visit workshop appears' Engine coolant level OK and not overheating. Any ideas what the cause is? - or has anyone experienced the same problem - trying to avoid expensive Mercedes garage bill!
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post #2 of 5 (permalink) Old 10-31-2008, 01:03 PM
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Bad coolant temp sensor or bad fan relay would be my suspects.

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post #3 of 5 (permalink) Old 06-04-2013, 06:00 PM
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Did you check all the fuses are ok? I don't know how many fuse boxes your car has, but mine has 3: one in the trunk and two in front. Be sure to check them all. If problem is persistent After this i think you will have to check and have your car diagnosed with a star equipment to read and see potential issues. Be sure to print all the fault codes during computer diagnosis, ask them to print fault codes. DO NOT EREASE FAULT CODES BEFORE PRINTING. Erasing should be performed in the very end of the process.

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post #4 of 5 (permalink) Old 06-04-2013, 07:23 PM
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I would start with checking the thermostat.
No fan working on max in summer temperatures can cool down the engine to 40C with closed thermostat.
So it is bad thermostat, or bad temperature sensor.
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post #5 of 5 (permalink) Old 06-04-2013, 08:26 PM
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Before doing anything else i would recommend performing these steps:
1. Turn on the engine.
2. Wait until the max temp is reached.
3. Open engine cover and locate the fuse box (driver's side), also remove the fuse box cover.
4. In the fuse box locate the engine coolant motor's fuse (it must be a high amerage fuse)
5. Without turning off the engine, remove that fuse. Check for possible oxidation on it's contact surfaces and remove it using a knife or scratching it.
6. Insert that fuse. If the engine coolant motor turns on at max speed, you have an electrical problem.

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