C216 radiator fan super loud

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New Member
Mar 10, 2012
Bedfordshire, UK
Apologies if this has been resolved in the past, or if this has been posted in the wrong place.

I have a 2007 CL500 C216 with 86k miles on it, and the fan runs at a very high speed once the car is up to operating temperature. It is super loud when it runs this fast. It may slow down here and there, but once the coolant temp is at 82ish C, it's on pretty much all the time and is loud. A/C still works fine. The temperature on the dash has never gone past about 85C.

So far, I have changed the thermostat, and have flushed the coolant twice, and am wondering what to do next. I'm thinking water pump. There seems to forever be air in the system, although there are no leaks I can see.

When I have disconnected the fan momentarily with it running at high speed, to see how hot the radiator is, immediately the yellow coolant symbol appears on the speedo, and the radiator is usually warm, but not hot. Same goes for the expansion tank, its fairly warm, but not 80C hot.

I noticed today that when reinstalling the air filter housing, as I was tapping it in to place with my hand, the fan turned on for a few seconds and stopped. I then tapped the ECU (bosch me 9.7), and again the fan spun up then stopped even though the engine was off. This now makes me wonder if the ECU is bad. I also have been getting a P2088 code, which relates to the cam adjuster magnet, so i replaced all 4 cam adjusters, and still get the code reappear on a daily basis. I can't see any evidence of oil having leaked in to the wiring harness from the old cam adjusters, nor do I think it is premature wear on the idler gear which i know can happen on the M273 engine

My thinking is that if it was the Ecu, then why does the fan at full speed only happen after the car has gotten to operating temperature, and not before. Having the A/C on or off makes no difference. But on the flip side, if it was the Ecu, it might explain the P2088 code.

And advice or suggestions would be very much welcome. Thanks

EDIT: I should add I've used icarsoft MB II, and the only odd things I noticed was the intake air temperature was a found 50C, unplugging the MAF sensor made no difference to the fan. Also, the transmission fluid was always around 55C, so it wasn't that I presume. The request for engine fan never went about 25% at any point, nor does it change when the fan spins up or spins down. Car has been maintained well over the 4 years I've had it, oil change every 5k miles.
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One thing I know is that if the fan controller cannot read the (CAN bus) engine temperature, it should run at maximum speed in order to protect the engine regardless if the engine has reached its operating temperature or not. I can think that an erroneous value also triggers this behavior. Before taking your CL to a mechanic, I suggest a thorough examination of all cables and connectors in the engine compartment. Look for connector elements not properly seated in their housing or green goo, indicating moisture induced corrosion.
I see that this is an old thread already but I have exactly same symptoms (been over a year already). Three workshops have investigated without results. Fan has been replaced also. Did you find the cause, was it ECU? Thanks!
I'd do a coolant test to see if there are any combustion gases getting into the cooling system. If everything is functioning as it should and no codes are reported, it may just be working harder to keep the temps down.
I'd do a coolant test to see if there are any combustion gases getting into the cooling system. If everything is functioning as it should and no codes are reported, it may just be working harder to keep the temps down.
Hi - I started this tread almost 2 years ago, and the issue has not been fixed, and the car has not been driven much in that time, but I do have a few updates to (hopefully) prevent others from making the mistakes I made.

In addition to the original post I made, the radiator fan comes on as soon as the car is started and the engine is cold. A fist tap on the ECU stops the fan spinning at full speed almost instantly. There is also a battery drain issue, I have installed a remote kill switch to disconnect the battries for this.

I got the car checked for combustion gases in the coolant, and there wasn't any. Head gasket is fine. I changed all 4 cam adjusters, but that made no difference to the P2088 code. There is no oil in the wiring harness, nor inside the ECU. All cables were checked and connectors were cleaned with eletrical cleaner. There was no green goo or signs or signs of moisture ingress. I then took the lid off the ECU, which was not easy, but was do-able. There was no sign of water ingress/oil inside. Nor could I see any evidence of a blown capacitor. I gave the board a clean with some electrical contact cleaner, cleaned each pin and put it back together. Made no difference. I am certain it is the ECU, so am going to see if I can get it repaired next week. Will update this post once that has been done.

I wonder if the battery drain is being caused by the ECU. Dunno, thats a guess.

The reason I have not had the radiator fan replaced is because the tap on the ECU stops it being on full speed.

To any prospective buyers; I don't believe a CL 216 of any variety can be a reliable daily driver now that the electrical modules are 'old' as my 2007 one has shown me. If you are going to get one these, then you are going to have to be prepared for significant down time, and will need a more reliable daily driver. My second car has been a 2006 BMW 630i, which is a far more 'analoge' car, far fewer modules and no hydraulic suspension to worry about. As trefin has said earlier, it's really hard to get an accurate diagonosis on these cars, becuase there are just so many modules, and as good as Star diagnostics is, it is not perfect. For instance, when my non-logic 7 amplifier in the boot failed, I had the car scanned with a Star diagnostic scanner and it found no errors. Also I dont believe a faulty ECU will show up with Star, instead you will get the phamtom codes the faulty ecu is generating, and could end up throwing time and money at an issue that doesnt exist.

I had this it is the AIRCON sensor at lower front of the radiator.

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