Cooling Fan wont cut in

Probably the head gasket is gone, which causes air locks. Tell the garage to do a gas test above the coolant, this will show that the head gasket is leaking.

MrCheerful explained on 10/05/2007 :

I will agree with that. I would guess the sensor is not seeing the true coolant temperature because it is in air(lock). The same thing can happen to your gauge, in that the temperature can appear to fall once the water level falls below its sensor/sender unit.

Have you made any attempt to ensure there are no air locks in the system? Try topping it up with the car facing up an incline, with the engine running and the filler cap off until all of the air is expelled.

I'm pretty sure the switch on these is mounted part way down the radiator, so you'd have to loose quite a bit of water for the switch to get air near it.

Plus if it's happening on the motorway, it's not a cooling fan issue, as there should be sufficient airflow through the radiator while travelling at speed. I'd be looking for blockages (a coolant flush wouldn't go amiss on something that old), a faulty thermostat, or a faulty waterpump (impeller fallen off the spindle).

First thing to check is if both top and bottom radiator hoses are hot when it overheats. If the bottom one is significantly cooler, then there's a water flow problem somewhere.

Isn't the thermo switch on the very top of the thermostat housing on these???

Tim..

The sensor usually simply detects the temperature and informs the ECU which then decides when to put the fan on. So if it is a cooling fan issue only then it is possibly the ECU at fault. If this is the case bypass it with a manual switch. I have on my car as I had exactly this problem.

"gazzafield" wrote in message news: snipped-for-privacy@pipex.net...

No, on this age of 'Scrot (infact all scots) the thermo switch acts directly on the fan motor (sometimes with a relay), the ECU isnt involved.

Tim.

Not just Escorts either. AFAIA most electric fans operate in the same way. Mike.

Only on vehicles of the Escort's era.

Chris

Is it actually overheating - or just the gauge saying it is?

hmmm...now I think about it, the diesels had the switch mounted on the bottom of the thermostat housing, so every chance the petrols had it in a similar area....