I'm now in pretty desperate need of help and tried everything after reading all I can from the forum. Really hoping someone has the answer! PLEASE...
Problem: engine runs fine and car runs well. Once it's up to temp and idling the expansion bottle fills, pressurises and eventually the cap is overcome until I pull the plug off the sensor to activate the fan and blip the throttle to flow the coolant. After that and with the fan still running, the coolant immediately drops back down to where it should be and does not boil again.
The fan never trips on by itself. It only comes on when I pull the plug on the temp sensor on the thermostat housing. The fan is very effective and it can then sit there all day idling and the coolant doesn't rise back up or show any signs of misbehaving.
There is plenty of hot air in the cabin also suggesting there isn't an airlock.
In an attempt to cure this I have fitted a new expansion bottle and tried 2 new caps. Changed the water pump for a minispares EVO, fitted a new thermostat, new temp sensor in the thermostat housing, done the wiring loom upgrade, fitted all new coolant hoses, flushed the block through until clear water flowed, took the rad out and flushed that through also and it flows well. I can feel heat all across the entire radiator when it's up to temp. I have swapped relay for know good ones, filled with G48 coolant... and the heater matrix in the car is relatively new also. I just seem to be throwing money at it trying to fix this.
Am I correct in thinking that by pulling the plug on the sensor and the fan coming on that the ECU is functioning correctly, the relay is doing it's thing and there's no problem with that and associated wiring?
I don't see any symptoms of a head gasket failure. Oil and coolant are clear, I'm not losing coolant, there's no smoke out the exhaust and it runs well and behaves with the fan running. With the fan on it behaves just fine, so I don't think that's an issue
To summarise. With the fan running the car runs and behaves brilliantly. It's got a flushed and refreshed coolant system, but the fan fails to come on by itself.
I'm based in St Albans, so if anyone is local how to cure these issues, I'd be willing to reimburse with a few beer tokens!