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Radiator fan questions

908 views 1 reply 2 participants last post by  mxfrank 
#1 ·
I'm almost done working on my 190d, last couple of projects are to replace the heater blower motor and check out the radiator fan. There are two radiator fans, one behind the radiator and one in front. I have not seen either of them run. I have a couple questions, what is the difference between the two fans? What temp should they cut on? What's the normal operating temp and how high before you should start worrying about overheating? Thanks in advance!
 
#2 ·
The one in front is an electric fan. It has two speeds:

- Low speed is activated when the a/c system pressure exceeds a preset threshold (I believe it's 300psi). This pressure is above normal operating pressure, and so the fans won't always be on when the a/c is running.
- High speed is activated when the engine runs very hot. The activation temperature is different for each engine, but it's usually around 105C.

The fan behind the engine is usually actuated by a viscous thermostatic clutch (some engines use an electromagnetic clutch). Again, activation temperature will vary, but it's usually around 95C ambient AIR temperature for the viscous clutch. You should hear a difference when the fan engages. Test with your ears, not with your hands.

The calibration of these fans is very confusing, and I doubt it's ever perfect, because each event is triggered by something different: a/c pressure, coolant temperature, or air temperature. The theory is constant pressure...a cooling system will last longer and perform best if pressure variation is limited, and the way that's done is to keep coolant temperature in a very limited range. It's a convoluted design, but performance is usually reasonable. If you're running your Diesel up mountains in the summer, you will build heat, but in ordinary driving, temperature should be steady between 80-85.
 
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