Bit of advice please folks. W124 coolant temp gauge faulty

[silverback mike]

Hi folks
I picked up a lovely w124 260e today, didn't pay much for it and it drives beautifully. One snag though is that the coolant temp gauge doesn't work. Obviously I don't want to overheat the engine as presumably the fans won't cut in if stuck in traffic......

Any ideas? Thermostat? Coolant temp switch? Anyone know where the switch is?

Coolant looks ok and no sign of overheating / white stuff anywhere .....

All help appreciated, thanks, Mike.

[r129sl]

I don't think you need to worry about overheating. First, like most MBs of this period, the car has massive over-capacity for cooling. Most of the time, the thermostat will be closed. Second, the fan is on a viscous clutch, so it is not switched into operation but comes in as temperature rises. If I am wrong about that, the fans will default to "on". Other than that I can't help. I did find this image but I don't know whether it is right:

[silverback mike]

Thanks, I've had a good look, and fitting the sensor tonight, fingers crossed

[silverback mike]

r129, so, please correct me if I'm wrong, but are you saying that the fans are a separate thing to the actual gauge, the viscous fan is controlled directly by the engine rather than the gauge sending a signal to turn it on?

Sorry for being a bit dense, but your help appreciated.

[r129sl]

silverback mike said:

r129, so, please correct me if I'm wrong, but are you saying that the fans are a separate thing to the actual gauge, the viscous fan is controlled directly by the engine rather than the gauge sending a signal to turn it on?

Sorry for being a bit dense, but your help appreciated.

Exactly. The engine cooling fan is not an electrical component. It is belt driven. There is a clutch inside the pulley which engages or disengages as it gets hotter or colder. The engine cooling fan is behind the radiator. The fan or fans in front of the radiator are for cooling the air con condenser. They are electrically driven and are switched by a pressure switch (not a temperature switch) in the air con system.

Useful thread here: http://www.benzworld.org/forums/w124-e-ce-d-td-cla...

And this is a brilliant resource: http://www.w124-zone.com/downloads/MB%20CD/W124/In...

Edited by r129sl on Wednesday 8th October 15:46

[silverback mike]

Thanks for the help, appears to be fixed although maybe running a little hot? about 90 degrees?

[r129sl]

90 is fine. According to the workshop manual, the thermostat starts to open at 85 to 89 deg C and is not fully open until 102 deg C; and the viscous fan clutch does not engage until 96 to 104 deg C. There's plenty of headroom in MB's cooling systems. I drove a r107 500 SL with no radiator and no coolant for a couple of days (accident damage) and it didn't suffer.

[silverback mike]

Thanks for your help, much appreciated, I've just mentioned in the other thread, I'm taking the old girl through the centre of Bristol in the rush hour soon. Make or break