T/D twin cooling fans

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rutter123
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T/D twin cooling fans

Post by rutter123 » Sun Aug 14, 2016 9:48 am

Should they both come on together? I have mine set to cut in at approx 88/90 degrees c, but only one cuts in on the offside. They both work with a direct 12v or are they set to cut in at different stages? Non aircon.
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Re: T/D twin cooling fans

Post by TizzyD » Sun Aug 14, 2016 12:26 pm

As far as I know, one fan should cut in at a set temp say for example 90oC, then if, with one fan running, the car finds that that isn't sufficient it should cut in the second fan at a higher temp of say 98oC. That is my understanding of it, but I think people wire in an override switch to manually turn on one or both fans to aid cooling in stop/start traffic to prevent the car getting to overheat levels.
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Re: T/D twin cooling fans

Post by rutter123 » Sun Aug 14, 2016 3:34 pm

I have fitted a digital temp gauge and a different sender unit in place of the "death lamp switch" this is from a Fiat and is set for the first fan to cut in at indicated 88/90 degrees, i have never had the second fan cut in tho technically it does work, i guess this will only cut in under extreme circumstances. According to my temp gauge even on the hottest day in traffic 1 fan seems efficient enough to cool the engine down to about 74/76 degrees, i may fit a a manual overide to the second fan just as a precaution, best to be doubly sure.
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Re: T/D twin cooling fans

Post by TizzyD » Sun Aug 14, 2016 5:36 pm

Like wise, I too am tempted to fit a manual override to the fans, one to each so I can turn one on independent of the other or have both on at the same time. I will probably look into doing this before the Citroen Challenge in France next June. I think I've only ever had both fans cut in once and that was upon arrival at the ICCCR in 2012 but they were only on for a minute or two before it cooled down enough.
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Re: T/D twin cooling fans

Post by mds141 » Sun Aug 14, 2016 7:24 pm

One or two of the derv BX's were getting a little hot under the collar on the 2012 Classic Challenge. The petrol versions were fine, but the Valvers did struggle with the altitude in the Alps, 2025 M was our highest point if memory serves.
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Re: T/D twin cooling fans

Post by TizzyD » Sun Aug 14, 2016 8:56 pm

The altitude would be my concern, coupled with the turbo thats going to kicking out a load of heat into the engine bay. Im wondering at what point does the intercooler stop being efficient and if its worth rigging up some sort of water spray cooler for it :-k :-k
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Re: T/D twin cooling fans

Post by mds141 » Sun Aug 14, 2016 9:06 pm

I think all the dervs on the Challenge were N/A versions and they managed the altitude ok. Don't forget that at over 2000 M in the Alps it's still fairly cold, even in Summer. The dervs only started to get hot on the uphill descents in 30 degree temps. Tim's BX had a fan switch pack in, which was repaired at the roadside. If you're worried about overheating maybe a switch to Evans waterless coolant would be a good solution.
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Re: T/D twin cooling fans

Post by TizzyD » Sun Aug 14, 2016 9:11 pm

That Evans stuff maybe the way to go when the new aluminium rad and silicon pipes go on :-k all stuff to consider in good time.
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Re: T/D twin cooling fans

Post by rutter123 » Sun Aug 14, 2016 10:50 pm

Waterless coolant isn't that really quite pricey? i dont have any concern about altitude as im prob never gonna go above 2000m, The car has never overheated in its 294000 miles so i think i'll stick with the manual override on fan no2 as a precaution, the digi temp gauge seems fairly accurate tho prob not spot on but certainly gives a good idea of wots going on under the bonnet, to date it's never gone over 90 degrees before the fan cuts in, i change the coolant every 2 yrs which also helps to keeps things in check and that the waterways are not clogged and full of silt etc.
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Re: T/D twin cooling fans

Post by Jaba » Sun Aug 14, 2016 11:18 pm

rutter123 wrote:Should they both come on together? I have mine set to cut in at approx 88/90 degrees c, but only one cuts in on the offside. They both work with a direct 12v or are they set to cut in at different stages? Non aircon.
The answer is yes they always come on together. Each fan has a switching relay which links the two fans up in series for the first cut in temperature when they run at reduced speed. At the high temperature cut in each fan is connected to 12v directly and they both run at full speed.

You can test all this by removing the rad switch connector and shorting each rad wire to the earth wire. NB both must be earthed to get full speed running. Also check the 12v circuit feeding the LH fan if it does not come on at all.
You can test the rad thermostat off the car by heating it up in water while checking for the cut in temperatures with a thermometer.
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Re: T/D twin cooling fans

Post by rutter123 » Mon Aug 15, 2016 9:50 am

Ahh, now thats interesting, in which case i suspect i have a relay problem with the left fan or something is not as it should be, the right fan cuts in at full speed which is on the higher temp, so previous to this what you are saying both fans should cut in at reduced speed first. I have some checks to make.
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Re: T/D twin cooling fans

Post by rutter123 » Mon Aug 15, 2016 6:00 pm

I've had a quick check over and it seems only one fan is working on full speed, i have shorted each blue wire to earth and still only one fan works tho the relay is clicking in the bulkhead, is each fan controlled by it's own relay? or do both run on a single relay? ive put 12v direct to the non working fan and runs ok, i suspect i have a wiring issue.
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Re: T/D twin cooling fans

Post by Jaba » Mon Aug 15, 2016 6:34 pm

NB, as mentioned above, you have to short BOTH wires to earth together to get full speed this may be why you only see one running under test.

Also if a fuse blows (not sure which no. on TDs. It is F4 on petrol aircon cars but TD may be different ) you will not get twin fans at low speed. Check out the earthing of both wires together first though.
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Re: T/D twin cooling fans

Post by mat_fenwick » Mon Aug 15, 2016 9:08 pm

There are 3 relays for the fans; one is between them and links the earth from the first fan either to the +ve of the second, or directly to earth depending on whether operating in series or parallel. Then each fan has its own relay which is closed by operating the ignition switch. If the nearside fan runs (with the ignition on) when earthed, then either its relay or fuse 4 is the likely culprit. The offside fan I don't think is fused for some reason!
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Re: T/D twin cooling fans

Post by KevR » Mon Sep 12, 2016 12:50 pm

I've spent ages trying to understand the wiring of the twin fans on my TD and eventually gave up... Even when I finally found a wiring diagram (in the French Haynes - haven't seen one anywhere else) it didn't seem to make much sense to me. Then I found I had no power to the main relay in the fuse board, so the fans were never going to work normally. So I added an extra relay to power the original relay, and now they sort of work. I've also added override switches, and one thing I've noticed is that if I switch the slow one on, both come on slow, and if I just switch the fast one on then one fan goes super-fast and noisy - but switch fast and slow on together and both fans turn faster then slow, but slower than full speed, if that makes any sense.
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