Single speed Fan resistor - a bridge to far...

Thickasmud · Post by **Thickasmud** » Mon Oct 11, 2010 3:21 pm

Quick question to the experts. I have finally managed to replace the Thermostat, gaskets, and then radiator after the orange then red temp. warning lights came on, 2 weeks ago. Now I find that the fan fails to start when the thermostat opens and rad becomes hot. I bridged the rad fan switch with the low speed relay (silver cylinder beside n/s headlight) also bridged and the fan started so I presume that either or both relay and fan switch are kapput. I have ordered the fan switch, but until I discover whether the engine head is junked am loath to spend even more in the hope all is well.
Assuming the new fan switch does the trick and allows the fan to come on at the lower switching point, can I leave the relay wires bridged to see how the car runs for a week or so? Or will that then burn out the fan?

toddao · Post by **toddao** » Mon Oct 11, 2010 6:10 pm

It does sound like the rad fan switch has had it and it seems that the best ploy until you replace it is to have the fan on via your bridge. I'm sure it will be alright, better loose the fan than cook the engine!

electrokid · Post by **electrokid** » Mon Oct 11, 2010 7:05 pm

If the layout of your BX wiring is the same as mine there are 2 places where corrosion of the connectors becomes significant in the fan circuit.

The rad switch itself is mounted at the bottom of the rad directly under the filler cap - so not only subject to splashes from the road it's also in line for any water coming out of the rad overflow. Wiring goes from there to a connector behind the NS headlamp - if the position of this is disturbed from its original position then it can be drenched by rainwater draining around the headlamp.

Plug and remove both connectors several times to clean the contacts. To check the operation of the fan use a knife blade such as a Stanley knife and insert it between the plug and the housing on the rad switch being careful not to short it to bodywork while doing so. Do this without removing the plug - this also checks the connectors.

The fan shouldn't come on as soon as the engine thermostat operates - only when it gets too hot - from memory that should be 88°C.

A rad switch that is off the car can be checked with a meter or a battery and bulb - arrange so that the meter or other arangement will show when the switch goes short circuit. Boil up a mug of water in the microwave and put the switch in it dangling on the wires connected to it - the switch should go short circuit quite quickly.

Periodically check the fan operation with the stanley knife to be sure it's operating.

Thickasmud · Post by **Thickasmud** » Mon Oct 11, 2010 9:24 pm

Totally fed up now. Have replaced the Fan Temp switch with a new one, left the relay bridged, replaced coolant and bled from the various hoses took the TGD for a spin stopping couple of times to top up then ```````````````````````````````````````'`'thats a hissing sound" up goes the bonnet, yep the top thermostat housing hose has split. Every tool used so far I threw in the boot before leaving, except a blade of any sort, needed to cut a fresh end to re-attach. 30 minutes walk each way and more coolant tipped in and guilty hose reattached.
After 20 minutes of driving around hoping no further problems would crop up, parked up but left car running to see if fan would operate. Needless to say it did'nt, ......then water erupted everywhere as another hose split......fuming more now than the car and at 175k miles thats saying something.

Too put this into context; Removal of thermostat resulted first in sheared bolts which needed to be drilled out, then disintegrating thermostat housing body as that s'&^@$£.h of a circlip fought to remain in position. Problems getting the correct thermostat, even more problems sourcing the correct housing gasket...then on removal of radiator to flush out, the small outlet nozzle snapped as I attempted to release the original jubilee clip clamping the small hose.
When I now ring the citroen parts dept.I no longer need to say who or what car I need parts for, they tell me "That'll be for THE BX then! Irony, sympathy or sarcasm I cant quite decide. Rant over....

scarecrow · Post by **scarecrow** » Mon Oct 11, 2010 9:32 pm

Sounds like a shit day mate, to say the least! Better luck tomorrow. Can't you get them to give you a discount on parts as you're a regular now?

electrokid · Post by **electrokid** » Mon Oct 11, 2010 10:47 pm

When the orange then red lights came on - how long / how many miles and what speed were you doing before you eventually stopped ?

Kitch · Post by **Kitch** » Mon Oct 11, 2010 10:56 pm

Hang on....are you expecting the fan to kick in when the thermostat opens? Because it won\'t, it\'ll kick in when the coolant around the switch hits 95degrees C.

Sorry if I\'ve misread it and are teaching you to suck eggs, but thats how I read it.

Thickasmud · Post by **Thickasmud** » Tue Oct 12, 2010 9:03 am

Thanks for the posted replies, its a new day and at least the sun is shining.
Kitch I had hoped that after @5-10 minutes of the new thermostat opening and the car remaining stationary at idle the fan would cut in, obviously with the warnings about orange and red warning lights i am hesitant to allow the engine to get much hotter. It (as she is now known} is an Auto Diesel BX19.

Electrokid, the warning orange came on whilst stuck on the A20 approaching "Five Ways" on a Friday rush hour, outside lane no where to go, went red and stayed red, kept all her coolant though, at least 10 minutes before I could stop and that may well earn me a non red light stop if the IR was working.
What puzzles me slightly is I now do not recall EVER hearing the fan, but I have covered at least 30k miles in the last 3 years and never before seen the orange warning light.

I think perhaps I should concentrate on which hose has now split, double check the fan is still working then find and clean the earth connections for the coolant temp switch and the coolant fan switch.

Can somebody please suggest where the earths are located?

electrokid · Post by **electrokid** » Tue Oct 12, 2010 10:07 am

Ten minutes with the red light on is probably way too long. That happened to me on the M4 - again - nowhere to go and very running very late - I wasn't far from my destination but carried on - that damaged the head (not on my current BX though) - and I suspect that is what has happened to yours - you wouldn't get coolant pipes popping unless there was excess pressure there and that's almost certainly from a crack in the head or head gasket problem.

after @5-10 minutes of the new thermostat opening and the car remaining stationary at idle the fan would cut in

On the diesel this will only happen on a warm day anyway.

I now do not recall EVER hearing the fan,

You can get away with not having the fan operational for several years if you don't have any other problems or get stuck in traffic etc - even when working it very rarely operates - which is a problem because the connections etc can fail without you knowing about it.

Out of interest I checked the temps of the sensors fitted...

The switch driving the orange light is almost invariably part no. 0242 43 and operates at 105°C. The switch driving the red light could be part no. 0242 49 operating at 110°C or part no. 95 579 684 operating at 112°C. Water at +10psi (which is what the pressure cap on the rad should set it to) boils at around 115°C so there is very little margin for error - any driving with the red light on and you are looking at damage to the head / head gasket.

A variety of rad switches were fitted which operate at some point within a quoted range of temps...

Part no.............temp range
26414...............79 to 88°C
126416..............79 to 84°C and 83 to 88°C (double switch - 3 pins)

From memory the earth for the fan is somewhere near the connector behind the NS headlamp - find the connector and follow the wiring back to where it is earthed - but I think the fan itself is the least of your problems - you shouldn't need it this time of year.

One tip for an overheating emergency - if the orange light comes on and if you suspect the fan isn't working then turn the heater on to max heat and the blower on to max - this will take some of the heat out of the engine even if you have to open all the windows to stay sane.

Post by **mat_fenwick** » Tue Oct 12, 2010 10:20 am

I am really sorry to be the possible bearer of more bad news but the hoses splitting sounds like a symptom of excessive pressurisation in the cooling system, perhaps from a failed HG after the overheating.

I would suggest you leave the filler cap off to keep the pressure down (you may even be able to use the car like this for a while if the HG has failed) and check for bubbles in the coolant.

I don't think the silver cannister is a relay but a resistor. I'm not too familiar with the single fan set up on BXs but would imagine it's the same as other PSA cars of the era. From memory there is a live feed to the fan and the earth lead goes via the fan temperature switch. When the engine is hot the fan is earthed via the resistor and spins slowly. If the temperature continues to rise then a second set of contacts closes in the temperature switch and earths the fan directly, so it should spin fast.
I believe the point of this was to minimise arcing in the temperature switch, and prolong its life.

EDIT - we posted at the same time, sorry for some duplicate information!

Was the heater blower on when you were idling the car? I've got a gauge and on a cold day with the heater on the engine will never warm up to the point at which the thermostat opens. So it may well be that the heater is taking enough heat out of the engine for the rad fan not to come on. Best of luck!

Thickasmud · Post by **Thickasmud** » Tue Oct 12, 2010 2:22 pm

"C'est la Vie", seems appropriate along with a thankyou to all who corresponded.

Cleaned all the earths, rechecked the contacts topped up and went for a longer spin, left @15 mins and an important, if small triumph, for the first time in my brief ownership the fan burst into life.

Sadly the build up of pressure is forcing coolant out of the rad cap confirming your posts that the HG &/or head have failed. When the engine cools down I will do a final check for air bubbles on startup, before reading her the final rites.

She passed the MOT mid August, so has 10 months to run.
Last week - New Radiator, thermostat, fan temp switch and gaskets
Aug 2010 - reconditioned steering pinion, new frnt return pipes, new rear tyres.
2009 - Small Octopus, headlight, inner frnt arches welded, new frnt tyres
front suspension bushes, fresh LHM filters, new main octopus.
2008/9-Reconditioned Diesel fuel pump, new rear engine water pipes.

She was a real pleasure to drive (pain to own) and if anyone wants to take on what is now a quite rare Auto Diesel in the knowledge of the above it would be some consolation for the blood and near tears most recently spent. She is taxed until the end of this month, any offers?

Thickasmud · Post by **Thickasmud** » Tue Oct 12, 2010 2:32 pm

Meant to add in reply to Matt, yes the cabin heater blower was on max during the entire episode.
The heater matrix tap being "welded" to the hot position, {useful in winter and permissible in summer due to the sunroof} draws plenty of heat from the system at all times, but not enough, clearly!

Kitch · Post by **Kitch** » Tue Oct 12, 2010 10:13 pm

To be honest, hearing the fan actually cut in on an N/A diesel BX is usually bad news....they just never need to work! Sounds like possible H/G but not a particularly tricky fix TBH.

Post by **mat_fenwick** » Tue Oct 12, 2010 10:24 pm

electrokid wrote:any driving with the red light on and you are looking at damage to the head / head gasket.

That's why I've replaced the 110°C switch with the 105°C one - so if I don't notice the gauge creeping up I should at least have a warning light in time to allow me to do something!
A shame to hear the car is being given up on - it's a fairly simple job to do on an non turbo. I know how you feel though, various times I've felt like throwing in the towel with things mechanical. Many years ago I relieved such a frustration by embedding an axe in my workbench...it didn't help in the slightest with the bushes I was trying to press in but it made me feel a hell of a lot better!

electrokid · Post by **electrokid** » Tue Oct 12, 2010 11:07 pm

A shame to hear the car is being given up on - it's a fairly simple job to do on an non turbo.

Yes it is - and because the car is still running it's more likely to be just head gasket rather than head damage as well. Even if the head fails pressure test there's probably one around on BXClub somewhere.

I've felt like throwing in the towel with things mechanical. Many years ago I relieved such a frustration by embedding an axe in my workbench...

Felt like that yesterday ! Fine weather - finish off workshop extension by putting the cladding on the front - needed to put a groove in the cladding timber so made a jig for the router - it worked very well - for the first 7 out of 24 lengths - then it grumbled violently and emitted loads of smoke before throwing the trip in the extension lead

Went to the local HSS to see if there was something decent - maybe a Makita - for a reasonable sum - there was - at around £130 which was ok - but it was marked up as 1/4" and it had a 1/2" chuck fitted - adapter might be available but it would have to be ordered - all my router bits are 8mm

About 5.30 now and feeling baulked at every turn I went on line - ebay - no - google - perhaps - Amazon - aha - Bosch - £76 - ' if you order in the next 23 minutes you can have it by tomorrow' - oooo yes please

Arrived just before 12 - nearly half the cladding done