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Matt
Matt, Mechanical Engineer
Category: Mercedes
Satisfied Customers: 20578
Experience:  BEng hons Mech engineering, in auto industry 22 years
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I have cl55 on a02 plate with an overheating problem it runs

Customer Question

hi i have cl55 on a02 plate with an overheating problem it runs on about 80c when driving but when stationary engine running the temp soon starts to rise into the red my local garage has taken out the thermostat & flushed out the cooling system & seems to think that the fan does not appear to run on fast speed many thanks steve
Submitted: 3 months ago.
Category: Mercedes
Expert:  Matt replied 3 months ago.

As a very first check make sure the coolant level is correct / up to the mark on the tank, then I'd first check that the radiator cooling fan is coming on as it should and if thats OK then replace the thermostat in the engine.

Whilst the thermostat is being replaced you might as well also reverse flush the cooling circuit (remove top hose to rad and use a hosepipe to push water into the engine until you get clear water out of the radiator hose) and top up with 30-50% fresh antifreeze. Also check that the small diameter bleed hoses that run from the top of the radiator and the top of the engine aren't blocked as this allow the air to vent back to the header tank automatically.

If you still have a problem then check that the water pump impeller / turbine isn't spinning on its shaft. You should be able to achieve this by removing the bottom hose from the engine and use a screwdriver or similar to feel for the water pump impeller blades, whilst your assistant turns the engine over by hand.

If you can stop the impeller with slight pressure from the screwdriver the pump needs replacing.

Also its possible the belt is slipping so its worth replacing its especially if the rubber ribs are cracked or it looks shiny on flat side of the belt - while its off check that the tensioner and other pulleys all spin freely the exception to this is the AC pump ( if fitted)

I'd also suggest ensuring that you've got all the air out of the system as this sort of episode can leave pockets of air trapped and prevent the coolant from circulating properly.

So check that the small hoses that run from the top of the engine and radiator that run back to the header / expansion tank are free flowing and not blocked

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