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R171 slk350 overheating?

2224 Views 4 Replies 5 Participants Last post by  phunn
Just purchased a r171 04 slk350 and noticed the radiator fan doesnt engage

Read around the forum but was only able to find info on the r170 so was not too sure if the same applies.

Did test the fan by turning on the in cabin fan to max and the radiator fan did engage. Not sure of the speed but it did seem fine.

Took it for a spin and saw that the temperature gauge did start to increase past the half way (80 degs) and creep to 90degs which wasnt a big deal i hope. But on one my trip after 30 mins of driving it started to creep towards 95 degrees where i decided to pull over so i did not cause any further damage.

Im not sure what the normal temp should be but based on the guage it looks like 80 -85 where the termometre is on the guage.

Just to give some idea the outside temp was around 80 degrees farenheight according to the car.

So i still have issues with the fan - did read it could be a module since the fan works with the a/c but no idea how to test or access it.

And with the a/c does the fan work at the proper speed or just a slow speed hence the high temp?

Also the car does not seem to give me an malfunction messages though i have not scanned the car either

Any help would be appreciated

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If the cooling fan doesn't engage when it should the car will report that through a message in the MFD. It will display the symbol of water with a thermometer. See your owners manual.
But otherwise I think your car is fine. 90-95 is the normal operating temperature. Mine is always around 95. No worries. If you still don't trust it have it checked at the dealer. I think they can test the fan with STAR.

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Sneaky Pete is correct that the fan and the overall cooling system can be checked and confirmed operating correctly by the MB diagnostic system DAS.

The engine ECU controls the coolant temp and has a typical operating range of 80 - 100*C. Only once the coolant temp is above 110*C does the ECU consider the temp too high. I believe that is when you get the warning on the MFD. From what you describe it sounds like your cooling system is operating correctly.

The cooling fan operates over a wide RPM range and is used for both the A/C system and the engine cooling. It will cycle on and off and change RPM depending on the overall load on both the engine coolant and the A/C refrigerant. When at top speed it will sound rather loud as it is moving a lot of air. As with most every component on the car it is controlled by a controller that is receiving a data flow from various sensors. It is not simply on and off.
Welcome, cobber, to the Happy Band.
My '04 350 R171 would only engage its' (electronic; for avoidance of doubt it's not a mechanical fan) radiator fan when the engine became warm enough to require cooling. And that was pretty hot...
You say the outside temperature was 80 degrees, so it would be logical to expect the fan to engage after the engine had been running for maybe 10 minutes, but if the temperature gauge did not get very close to the 'red end' before you 'decided to pull over so i did not cause any further damage' then you might be suffering 'New Car Twitch', an ailment with which we are all familiar!
I presume your air con cut in quite quickly, given your outside temperature reading. The air con fan will deliver a small typhoon if the vents are open and the desired temperature is set (maybe at a nice San Diego 72 ish?).
Assuming the outside temp. gauge (located low down on the front bumper near the fog lights (left or right?; don't remember) was telling you true about the outside temperature, then the air con fan and the engine cooling fan should fire up, giving hope that all's right with the car. If the air con was not blowing a cool breeze than maybe the coolant needs topping up (my old R170 used to need that service regularly).
Either way, take the roof down and go for another ride... Love it.
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