Rad fan on when it shouldnt be??

[Tiny Tim]

Sounds weird I know...

I've recently had a new rad in, had a few issues with the bottom hose popping which i've now sorted, it stays on nicely BUT...

I've just been for a short drive after bleeding the system and the cars 'up to temp' - its sitting nicely at 80degrees as it has done previously. On the way back home i've noticed this sound and thought to myself...surely thats not the rad fan.. I pull up to find both fans on full... Can anyone shed some light on why? They turn onto low when I switch the ignition off and the other weird thing is that the bottom rad hose is cold. Anyone got any ideas?

Its a 2.1TD D8

[mjb]

Coolant temperature sensor at a guess. There's 2 of them (at least on the petrol turbo model), one for the dash gauge and the other for the ECU

Or it could be something simple like a massive amount of air in your system or the thermostat needing replacement.

If you have aircon, does it happen with the aircon turned off ("eco" on models with climate control)? The reasoning being is that while the engine/coolant/radiator may be at a sane temperature, the a/c heat exchanger gets HOT when in use meaning the car has to keep activating the fans to keep it cool...

[Tiny Tim]

No, its a non-aircon model... i cant afford luxuries like that

Well the fan hasnt come on this morning after my 7 mile drive to work stop-start... the bottom rad hose however is still cool... think i'll try re-bleeding it before looking at the 'stat etc

[Tiny Tim]

Oh, while im here. Am I right in thinking the stat sits on the end of the head behind the air filter on the 2.1TD's? - My Haynes has gone walkies

[mbell666]

i think on all the diesels it sits in the housing where the top rad hoses connects to the engine.

[Tiny Tim]

Thanks, i'll take a peek this afternoon.

[Tiny Tim]

Ok, im confused now. After a run in the car and getting it upto temp, the bottom rad hose is still cool but the heater fan is blowing out hot air. Is this still likely to be a thermostat issue?

[teamster1975]

Ok, im confused now. After a run in the car and getting it upto temp, the bottom rad hose is still cool but the heater fan is blowing out hot air. Is this still likely to be a thermostat issue?

I'd change the thermostat for good measure; it does sound like it's gone faulty

[mbell666]

Is the rad top hose getting hot?

In theory the top hose should be hot and the bottom hose "cold"er. If the top hose is not hot (/pretty cool) then that would sign a dodgy thermostat to me.

Does the engine temp get above 90 or does it stay fairly constant around 90?

[Tiny Tim]

Temp sits a squidge (is that even a word?) above 80 on the gauge as it always has done. Top hose is hot as it should be and heaters blow hot when upto temp. Also, both heater matrix hoses are hot.

[mjb]

I'm going to stick by my saying one of the coolant temperature sensors is in mild need of replacement. Either the dash is showing too low, or the ECU is seeing too hot. Someone with an autodata cd should be able to tell you what the readings should be on a multimeter given a known temperature.

May as well change the thermostat while you're at it - it's only a few quid and you'll be working around the same place...

[Tiny Tim]

Ok, cheers for that.

Can you tell me where the two sensors sit? - is it the one I cleaned up yesterday that brought the fan on when I unplugged it? - Brown connector that sits in front of the thermostat housing?

[Tiny Tim]

Hmmm. Jut got home from work, opened the bonnet to find a hot bottom hose.... thats more like it!

Think i'll replace the 'stat just incase.

Thanks for all your help guys.

[steve_earwig]

...both fans on full

I thought you only got one without air con!

Yep, the stat should be wide open when it's up to temp, the heater feed's before the stat because you'd wait forever for heat on a cold day if it was behind...

I have a feeling the stat's somewhere almost impossible to get to on the 2,1. Hold on a mo... [Haynes Book of Lies] On the 2.1 litre turbo diesel models, the thermostat housing is mounted rear of the cylinder block on it's right-hand end; to gain access, firmly apply the glandbrake then jack up the front of the vehicle...[/HBoL] Oh boy

[Tiny Tim]

Oh joys. Can you even get in a 2.1 without having to jack the front up