Folks,
Got home from work this evening to a mysterious humming noise. An ear to the bonnet told me it was the cooling fans. "Odd" I thought. So I turned the ignition on and the temp display on the dash read about 75. "Bugger" I thought.
Then I realised that the fans were on despite the ignition being off. I detached the temp sensor from the radiator and the fans cut out. I felt the radiator and it was cold. The top hose was warm, pressurised and has coolant in it. I've taken a couple of pictures of the temp sensor, which I'm now suspecting. They're here:
http://www.oh.is.it/pic/index.php?path=rad
There's some blue deposits on the mounting, as you can see, and the connector itself is slightly damp. I didn't spot any other signs of moisture around there, such as on the air intake. I did, however, spot some salty-looking deposits on the oil filter.
I only got home about half an hour ago, so I'm going to have my dinner and let the beast cool before inspecting the coolant level. I changed it about three months ago, before the cold snap, and topped up about a litre at the weekend as I was off on a long journey and doing the old POWER checks.
Any initial thoughts, or things to check later? It seems strange that the rad is cold, am I looking at a dead thermostat too?
TD radiator problem
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I'm not sure that everything is not relatively normal as the fan should come on though this seems quite a cool temperature to be doing it:
1) check your level: release a bleed screw to see how far the level drops. Are the temperatures you see when driving low/normal..?
2) Feel your radiator, is it cold at the top and warm at the bottom.. suspect a leak, or a pressurised system that has dumped some water, possibly via the expansion tank rad cap.
3) If you plug in your sensor after tea, when the car is cool, and the fans come back on, your thermal switch is broken and gone short circuit.
cheers
Russell [:)]
1) check your level: release a bleed screw to see how far the level drops. Are the temperatures you see when driving low/normal..?
2) Feel your radiator, is it cold at the top and warm at the bottom.. suspect a leak, or a pressurised system that has dumped some water, possibly via the expansion tank rad cap.
3) If you plug in your sensor after tea, when the car is cool, and the fans come back on, your thermal switch is broken and gone short circuit.
cheers
Russell [:)]
I've just had a poke, and am surprised at what I found. The radiator had actually warmed up a little! I teased the rad cap off (with a nice chunky towel over my hand 
and after a slight pressure release shone a torch in the header tank to be greeted with...lovely blue coolant, full as at the weekend when I topped up!
As the cooling fan switch was damp, I took a hairdrier to the connectors for five minutes and plugged it back in. The fans sprang into life. Am I right in thinking that this switch contains a thermostat/temp sensor different to those on the cylinder head?
Dan: as I flushed the system and replaced the rad bottom hose before Christmas, I doubt the rad would be silted up. Unless anyone's got reason to think otherwise?
My current line in thinking is that the thermostat is alright and that at some point on the way home (probably not too long after setting off from work, it's about a 45 min drive and fairly free-flowing) the cooling fan switch failed, possibly due to a water short, and that the fans were on the whole way home. I've no way of knowing, as I had the radio on :-/ Since the fans never cut out, the water in the rad was cold but the coolant in the top pipe that never made it from the block to the rad was warm. After standing for an hour while I had my dinner, the temperature of the water evened out in the system (GCSE science and convection currents kicking in here thus warming the rad.
Sound plausible?
and after a slight pressure release shone a torch in the header tank to be greeted with...lovely blue coolant, full as at the weekend when I topped up!As the cooling fan switch was damp, I took a hairdrier to the connectors for five minutes and plugged it back in. The fans sprang into life. Am I right in thinking that this switch contains a thermostat/temp sensor different to those on the cylinder head?
Dan: as I flushed the system and replaced the rad bottom hose before Christmas, I doubt the rad would be silted up. Unless anyone's got reason to think otherwise?
My current line in thinking is that the thermostat is alright and that at some point on the way home (probably not too long after setting off from work, it's about a 45 min drive and fairly free-flowing) the cooling fan switch failed, possibly due to a water short, and that the fans were on the whole way home. I've no way of knowing, as I had the radio on :-/ Since the fans never cut out, the water in the rad was cold but the coolant in the top pipe that never made it from the block to the rad was warm. After standing for an hour while I had my dinner, the temperature of the water evened out in the system (GCSE science and convection currents kicking in here
thus warming the rad.Sound plausible?
Russel,
I've always thought that the running temp is a tad low, usually not getting above 80 or so unless stationary. I've been told diesels run cooler than petrols, is that true, and this much cooler? The heater's never been great at pumping out hot air (unlike my friend's Vectra, which almost melted my eyeballs last night) and seeing the current thread about a cool ZX and people mentioning head gaskets, I'm getting scared
I <i>think</i> the rad is normally fairly evenly warm. I keep meaning to put some newspaper by the expansion tank outlet hose to make any leaks more obvious. Perhaps I'll rememeber now
If it is the thermal switch, I'm thinking GSF part number T93485. A bargain at £7.75! Now the big question: how safe will it be to drive with the cooling fans disconnected, working on the assumption that the thermostat is okay? I don't really have the time to see to this until the weekend, and have to commute about 30 miles a day.
I've always thought that the running temp is a tad low, usually not getting above 80 or so unless stationary. I've been told diesels run cooler than petrols, is that true, and this much cooler? The heater's never been great at pumping out hot air (unlike my friend's Vectra, which almost melted my eyeballs last night) and seeing the current thread about a cool ZX and people mentioning head gaskets, I'm getting scared
I <i>think</i> the rad is normally fairly evenly warm. I keep meaning to put some newspaper by the expansion tank outlet hose to make any leaks more obvious. Perhaps I'll rememeber now
If it is the thermal switch, I'm thinking GSF part number T93485. A bargain at £7.75! Now the big question: how safe will it be to drive with the cooling fans disconnected, working on the assumption that the thermostat is okay? I don't really have the time to see to this until the weekend, and have to commute about 30 miles a day.
Hi,
I'm getting to the point where I think you may have no problem at all.
The fans cut in when the temperature is warm, even with the ignition off, and to cut in around high 70's or mid 80's is about normal for a diesel. Once cut in, the fans will stay on until mid or low 70's.
Do you have to do some slow speed manouevring before you park, or in the last bit of driving home..? Road humps or twisty lane or something..? I'm guessing your 30 miles from work goes fairly fast except the last mile or two..? So the work done by the engine when going faster cannot dump heat that quickly when you slow down, and the fan cuts in.
The fans do cut out when the temperature falls below 70 or so I assume..? The water system is full, and after 30 minute tea break was holding pressure, it went shuutfffpphh, didn't it?, but coolant didn't come charging out, it was full (as the coolant had expanded to max), and the rad is an even temperature.
At the moment, I think everything is fine. But if it's behaving differently to how it does normally, keep a very close eye on your coolant levels, temperatures, when fans come on and off etc.
cheers
Russell [8D][8D]
I'm getting to the point where I think you may have no problem at all.
The fans cut in when the temperature is warm, even with the ignition off, and to cut in around high 70's or mid 80's is about normal for a diesel. Once cut in, the fans will stay on until mid or low 70's.
Do you have to do some slow speed manouevring before you park, or in the last bit of driving home..? Road humps or twisty lane or something..? I'm guessing your 30 miles from work goes fairly fast except the last mile or two..? So the work done by the engine when going faster cannot dump heat that quickly when you slow down, and the fan cuts in.
The fans do cut out when the temperature falls below 70 or so I assume..? The water system is full, and after 30 minute tea break was holding pressure, it went shuutfffpphh, didn't it?, but coolant didn't come charging out, it was full (as the coolant had expanded to max), and the rad is an even temperature.
At the moment, I think everything is fine. But if it's behaving differently to how it does normally, keep a very close eye on your coolant levels, temperatures, when fans come on and off etc.
cheers
Russell [8D][8D]
Low down RHS (car's) on radiator you have 3 heavy gauge cables with a 3pole connector on the fan thermoswitch.
Unplug the connector - and clean/rub the best you can - on both mating connectors contacts. Try squeese the female contacts a bit for positive mating.
One of the cable connector contact's is earth - the other 2 is for lo/hi speed feed from fan circuit.
Note that it's the fan LO (ground) side that's controlled here - use a heavy gauge test wire - or you may get burnt from a glowing thin gauge wire !!
The HI side of the fan is feeded off one of the relays in the junction (fuse) box - in turn controlled by ignition key.
Bridging either of the 2 possible combinations on the cable connector (ignition on) should bring the fan run either lo or hi speed - indicating the fan electrical circuit is working.
If neither tests brings the fan on - you're facing a problem with the fan circuit.
If either of the speeds (usually LO speed) is not working - then it's likely the ALU can LO speed resistor - near the bonnet lock - that's a corroded mess.
VERY rarely the fan itself fails.
If the fan never cut's in (or only cut's in at hi speed) after prolonged engine idle & HOT radiator - then the thermoswitch is defective - a VERY common problem on BX'es.
Happily this thermoswitch is not expensive.
Unplug the connector - and clean/rub the best you can - on both mating connectors contacts. Try squeese the female contacts a bit for positive mating.
One of the cable connector contact's is earth - the other 2 is for lo/hi speed feed from fan circuit.
Note that it's the fan LO (ground) side that's controlled here - use a heavy gauge test wire - or you may get burnt from a glowing thin gauge wire !!
The HI side of the fan is feeded off one of the relays in the junction (fuse) box - in turn controlled by ignition key.
Bridging either of the 2 possible combinations on the cable connector (ignition on) should bring the fan run either lo or hi speed - indicating the fan electrical circuit is working.
If neither tests brings the fan on - you're facing a problem with the fan circuit.
If either of the speeds (usually LO speed) is not working - then it's likely the ALU can LO speed resistor - near the bonnet lock - that's a corroded mess.
VERY rarely the fan itself fails.
If the fan never cut's in (or only cut's in at hi speed) after prolonged engine idle & HOT radiator - then the thermoswitch is defective - a VERY common problem on BX'es.
Happily this thermoswitch is not expensive.
NEXT DAY UPDATE...
I left the fan switch disconnected overnight to allow the contacts to dry off (or more likely freeze) and fully expected to reconnect it this morning and the fans to kick in. They didn't :-/
Driving to work, the temperature only poked its head above 80 once. At least I think it was 80. The first mark on the temp gauge is 70, then there's a short way to the next (unlabelled) tick then about twice as far to 90, then about as far again to 110. The scale obviously isn't linear, but I think it must have been running at about 78 or so.
When I pulled up in the car park, there was that humming noise again - the bloody fans were on! Before last night I'd <b>never</b> noticed the fans be on when I parked the car, and it's not like we had a sudden tropical spell! And now twice in two journies. I disconnected the switch and they cut out again. I'll go and reconnect it in about an hour to see if they kick in.
I left the fan switch disconnected overnight to allow the contacts to dry off (or more likely freeze) and fully expected to reconnect it this morning and the fans to kick in. They didn't :-/
Driving to work, the temperature only poked its head above 80 once. At least I think it was 80. The first mark on the temp gauge is 70, then there's a short way to the next (unlabelled) tick then about twice as far to 90, then about as far again to 110. The scale obviously isn't linear, but I think it must have been running at about 78 or so.
When I pulled up in the car park, there was that humming noise again - the bloody fans were on! Before last night I'd <b>never</b> noticed the fans be on when I parked the car, and it's not like we had a sudden tropical spell! And now twice in two journies. I disconnected the switch and they cut out again. I'll go and reconnect it in about an hour to see if they kick in.
Well I've just been out there and found pretty much the same as last night: the rad had warmed up slightly, not as much as last night when I left it standing, but the top was slightly warmer than the bottom.
I reconnected the fan thermo switch and heard the twitching of bouncing relays inside the fan housing, so with a little bit of wiggling the connector the fans sprung into life. So now I'm pretty certain that the switch is at fault, as it's been standing for an hour now and had I not have disconnected them, the fans would possibly have been going all this time
The car's due for a 6k service in the next couple of weeks, so I think I might take to opportunity to replace the switch and possibly the thermostat too.
So long as I keep my eye on the temperature gauge, and pulling over and reconnecting as needed, there shouldn't be any adverse affects to running with the fans disconnected should there?
I reconnected the fan thermo switch and heard the twitching of bouncing relays inside the fan housing, so with a little bit of wiggling the connector the fans sprung into life. So now I'm pretty certain that the switch is at fault, as it's been standing for an hour now and had I not have disconnected them, the fans would possibly have been going all this time
The car's due for a 6k service in the next couple of weeks, so I think I might take to opportunity to replace the switch and possibly the thermostat too.
So long as I keep my eye on the temperature gauge, and pulling over and reconnecting as needed, there shouldn't be any adverse affects to running with the fans disconnected should there?
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RichardW
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This weather you're unlikely to need the fans, and they are probably not rated for continuous operation, so if you run them more or less continuously you might burn them or their wiring out. I'd run with them disconnected unless you spend a lot of time sitting traffic - but watch the temp gauge like a hawk! 10 minutes and you could rig a switch in the car to bring them on.
UPDATE - Finally got round to doing some work on Sunday and replaced the rad thermoswitch and the thermostat. I found a split, perished rubber sealing ring dangling limply from the 'stat. Did a full service too and changed the clutch cable (that was one dirty pig of a job).
Driving to work today was a joy, the car seemed smoother from the oil change and the clutch noticably lighter. When I parked up I popped the bonnet and ... no fans! Case closed, thanks folks.
Driving to work today was a joy, the car seemed smoother from the oil change and the clutch noticably lighter. When I parked up I popped the bonnet and ... no fans! Case closed, thanks folks.