Cooling - odd behaviour

[Roger Blassberg 0]

Rather odd goings-on in the engine cooling department. The auxiliary (electric)pump comes on with ignition, and goes off without over-run. So the pump is ok but its control is not.

 

The engine is running a bit cool, around 75 deg, rising a bit in slow traffic but not overheating (at least not according to the temperature gauge). I changed the thermostat about a year ago. Most oddly, the stage 3 cooling fan speed comes on in short bursts (typically 5 seconds) at indicated water temperature well below 90 deg, with ignition on, but if ignition is turned off the fan does not run at all, at either stage 1,2 or 3. I think the stage 3 fan is preventing the water getting hot enough to trigger "normal" fan operation.

 

Fuel consumption is as I would expect, no evidence of overfuelling so I think the blue sender is ok.

 

My theory, having read the "Definitive Guide", is to suspect the yellow, 4 pin sensor as a first port of call; it is not apparently telling the fan controller to switch on.

 

By the way, I have changed the radiator 3 pin sensor recently too.

 

What do you think ladies and gents? Next move is to bridge the wiring to the yellow sensor and see if the fan controller can be persuaded to come to life. Its rather dark now, so it will have to wait before I can check.

 

Thanks for all interest and (hopefully) solutions!!

 

RB

[fla 9]

Hmmm strange one. I've got a spare fan controller i use for testing if you want to rule that out?

[Roger Blassberg 0]

Thanks Hasan. I'll bridge the yellow sensor outputs first to see if I can coax life out of the fan controller. The thing that confuses me a bit is that the stage 3 fan comes on. Maybe the yellow sensor feed to the temp gauge is lying too and the water temp is very high despite the reading, but I don't think so - hoses didn't feel abnormally hot or over-pressurised, no steam or water coming from the expansion tank.

 

I'll check the fuse in the controller as well.

 

Speak soon,

 

RB

[Roger Blassberg 0]

OK it turned out that a previous owner had wired the stage 3 fan to come on when the thermo switch on the rad called for stage 2. And the thermo switch was faulty and not switching on stage 1 at all. So the fan was going straight from nothing to stage 3. I cleaned the contacts on the controller unit, replaced the thermo switch and the 4 pin ("yellow") sensor, and all is well again, including run on of the fan and electric pump. I'll leave the stage 2/stage 3 combination now that I have stage 1 back in action.

 

Best wishes

 

RB

[Roger Blassberg 0]

OK it turned out that a previous owner had wired the stage 3 fan to come on when the thermo switch on the rad called for stage 2. And the thermo switch was faulty and not switching on stage 1 at all. So the fan was going straight from nothing to stage 3. I cleaned the contacts on the controller unit, replaced the thermo switch and the 4 pin ("yellow") sensor, and all is well again, including run on of the fan and electric pump. I'll leave the stage 2/stage 3 combination now that I have stage 1 back in action.

 

Best wishes

 

RB

[fla 9]

Good to hear it was as simple as that!

[robrado974 1]

A quick fix , nice one !

[lewvw 10]

It's a gem of a cooling system eh? ;) Nice work sorting it.

[Roger Chatfield 0]

Out of interest, my electric cooling fan comes on whenever the ing is turned on (even when engine is cold), is this normal?

 

Rog.

[Roger Blassberg 0]

No it's not normal. Could be that the rad thermo switch is shorting out. Test by pulling the plug off of it and observing if fan still comes on. If it still does, there is a fault elsewhere (wiring loom or maybe yellow sensor, or fan control unit, or third sensor on thermostat housing if you have AC....complicated innit??)If it doesn't, the thermo switch needs replacing. It's a bit inaccessible, you need a 30mm deep socket ideally to unscrew it. The good news is that it is cheap, about £15.

Good luck

RB

[Roger Chatfield 0]

Sorry mate, I meant my electric cooling PUMP, not fan...

 

Basically as soon as I turn on the ign the pump starts running.

 

Rog.

[Roger Blassberg 0]

That's normal. It runs with the ignition on and also IF the fan controller sets over-run.

 

So nothing to worry about there.

 

Best wishes

 

RB