Technical ecu light , running hot

[reggi]

Hi guys. I'm a bit stuck on this one so any advice would be appriciated. The missus has got a 51plate seicento 1.1 mpi. The ecu light comes on whenever the cooling fan kicks in.( i've managed to borrow a computer and the fault is engine coolant temp malfunction p0115)
It hasn't got a temp guage so i'm working blind here but the heaters get that hot you can't hold your hand in front of them.
I thought the problem would be the thermostat but i've changed that and no difference.
I then thought the rad was blocked because it was not getting hot, but after letting some coolant out of the bleed screw by the expansion tank you could feel it fill up with hot water.( i've spent half an hour bleeding the system so it can't be an air lock!)
So now i.m stuck. When i reset the fault the light stays off untill the engine obviously gets too hot.

 

[fingers99]

Well, the fan works, so my guess is that the fault is not with the coolant temperature itself, but with the coolant temperature sender. Are there any signs of overheating?

 

[reggi]

It has overheated once when she was stuck in traffic. But after topping it up we've had this fault.(Its not loosing any water and there's no sign of water in the oil). She's been running it now for three weeks and it hasn't actually overheated but then again the weather isn't that hot at the moment. The heaters blow far too hot tho.
My confusion is, the fan kicks in when the engine gets too hot but the radiator is cold so its not actually serving any purpose.
Thats what made me think the rad is blocked BUT when you loosen the bleed screw by the expansion tank and let some water out the rad gets hot. I'm stuck!!!! Could the rad be part blocked?

 

[fingers99]

Unlikely to be part blocked rad. Could be air locked: try bleeding it again, bottom bleeder first, top one second (engine running, heater on).

Are you loosing any water?

 

[reggi]

It isn't loosing any water at all. I've got hot water coming out of both bleed screws. There is only two bleed screws isn't there?

 

[fingers99]

Yes, only two. I think Asteris and Kripit are probably the only folk here who actually know how the cooling system on the MPIs works! Certainly the ECU has some input into when the fan comes on.

 

[reggi]

I've bled the system abit more and the radiator does seem to be working. I've reset the fault code and taken the car for a test run. The ecu light stayed out untill the car was stationary for a couple of minutes(the fan kicked in and the light came on). Still not sure whether its a sensor at fault or the ecu is warning that the cooling system isn't working efficiently. Anyone got any thoughts???????????????????

 

[rallycinq]

The fan motor bearings can fail. The fan turns, but not fast enough to properly cool. Put a seperate supply to the fan with a small fuse in line, and see if it blows.

Cheers

D

 

[fingers99]

This looks good. Of course, the MPI is OBCII compliant, so the generic codes should apply. Might even be the wiring to the sensor (rather than the expensive bit itself).