Cooling problem

[mike35]

I have a 1.6 diesel JX engine. I was treavelling down the motorway yesterday, i switched my heaters to cold, and the radiator fan kicked in.I have had a new water pump and thermostat, head gasket and have bled the system and put a flush through it,i have also had a VDO just kampers guage fitted and it sits on rouhgly 70. Does anybody know the reason why this would happen? (Many thanks).

[kevtherev]

The fan switch is, as you know, on the radiator.
It activates when the coolant in the radiator gets too hot to dissipate heat normally.
Either the coolant is moving through it too slowly (radiator is sludged up), the thermostat is not fully opening (faulty or wrong temp stat) or there is a blockage along the lines (kinked pipe, sludge, air.)

You mention a gauge, is it a water temp gauge?
if so where does it take the coolant temperature from?

[mike35]

I have cleaned all the pipes and radiator through, so dont think there would be any sludge. Its a temprature gauge and is fitted to the sensor in the head water pump flange.

[kevtherev]

I have cleaned all the pipes and radiator through, so dont think there would be any sludge. Its a temprature gauge and is fitted to the sensor in the head water pump flange.

I'm just saying what causes the fan to come on and slow coolant will cause it.. I have found sludge is persistent, and thermostats even new ones are not 100% safe.
The temp that the gauge indicates should read higher than that IMHO
The aux waterpump is controlled by a relay, the relay is switched on and off by a coolant temp switch mounted in the coolant housing on the head.
it switches on at 104°c
The pump will run regardless of ignition switch position.
Is this working OK?

Is the rad fan switch the correct one for your engine?