cooling fans

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hvanman
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cooling fans

Post by hvanman »

Hi, maybe a timely question with all this hot weather that may be useful to others... (and i am about to take the TZD on a run down France)

I have never heard my fans run so i did a quick check by shorting relevant connectors at the rad sensor. I can get both fans to run full speed shorting one pair, but no life from what i assume is the slower running pair via a resistor. Does anyone know where the resistor is and is this a likely culprit and this test only proves the fans run, is there a way to test the sensor and rest of the circuit without removing it? Where do the relay(s) live?

Many thanks, simon
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Re: cooling fans

Post by Jaba »

There is no resistor in a twin fan setup. The fans run in series at the slower speed through a couple of relays. Are you sure it is running in test mode at high speed ? I think it is more likely that you are seeing low speed running as you have to short both rad switch pins to earth to get high speed.
I could be wrong of course as not all cars are standard.
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Re: cooling fans

Post by Brian »

Hi Simon.

To test:

1. Pull the plug from the switch.
2. Look at the plug and configure as a U.
3. Ignition on.
4. Connect the bottom of the U with a link wire to the left, should run the fans on slow
speed.
5. Connect the bottom of the U with a link wire to the right, Should run the fans at
high speed.

If one or other of the test fail, then the switch may be faulty.

The switch can be tested in a kettle, battery and bulb to each circuit in turn, heat the water and watch for the bulb to light.

If you have a temp probe, this will indicate the temperature the switches turn on / off.

I see you are in Bedforshire, I do have some tested spares, you are welcome to a working one if this test fails.

I think this circuit runs series parallel.


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Re: cooling fans

Post by rutter123 »

you will be waiting a long time for the fans to cut in if you are just running at idle, i have recently fitted a digital temp gauge in the tzdt and have found even on these really hot days in traffic the fan rarely cuts in, at idle in traffic the gauge shows 70-80 deg the fan cuts in at 86 deg, can also be told by a small dip in idle rpm, another option is to fit a a lamp on the dash wired direct to the fan switch so you know when your fan is running. always a good secondary measure with a bx, dont rely on the lamps of death it will be too late!!
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Re: cooling fans

Post by hvanman »

Many thanks for the replies.

I looked at the haynes diagram and assumed it was a resistor but can see now it would be a relay.

Shorting the bottom of the u to one side makes them run, but shorting it to the other side nothing happens. I will try again to see which side is not working. As this test is bypassing the switch, maybe it is a relay or wiring fault, does anyone know where these relays are located? My car does look like it has had some wiring altered in the engine bay by a PO..

Thanks for the offer Brian, i will see how i get on with the relays before then testing the switch itself.

I like the idea of the indicator light, as its any easy way to see whats happening.. i may also fit a temp bypass switch as time is short before i go away.

I would like a guage, has anyone fitted an after market one and if so is there a specific one that is easy to fit the sensor into the system?

Many thanks, simon
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Re: cooling fans

Post by mat_fenwick »

The relays are located under a black plastic cover near the battery and next to the rear washer bottle.
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Re: cooling fans

Post by hvanman »

Thanks, I will have a poke around.....
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Re: cooling fans

Post by hvanman »

Well on checking again the fans themselves and relays seem fine. Shorting to one side and then the other does make the fans run slow or fast.

I then thought I would check about fitting an indicator light and over-ride switch and I am now confused... The Haynes Diesel manual shows the sensor switching an earth to the relay(s), but if I put an earth to either side of the "U", nothing happens??
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Re: cooling fans

Post by rutter123 »

for a dash mouted lamp i just tapped out the back of the fan switch, closed cuircit side to 1 side of lamp other side of lamp to earth. i used a yellow 10mm lamp mounted just next to the digital clock on the other side of the clock is a 90 degree warning lamp which is in place of the 112 degree "death lamp"
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Re: cooling fans

Post by hvanman »

Thanks, the diagrams I saw showed the switch was connected to earth rather than 12v. I've rigged up a temp box in the cabin with an orange led for the slow fans and red led for fast fans and a manual over-ride switch and will see how it behaves on the weekly M25 run in heavy traffic....
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Re: cooling fans

Post by rutter123 »

i believe the twin two speed fans were fitted on the t/d and cars with air con, moreso to aid cooling under heavy load i.e towing a caravan etc, i cant say whether mine on my t/d have ever run at high speed, but i do know they cut in @ 84/85 deg. always good to have a back up, many diesels have suffered sudden death syndrome due to lack of warning.
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Re: cooling fans

Post by hvanman »

Yes I've never heard mine and they do make a noise when running....

For the 90 degree warning light did you change a sensor on the thermostat mounting, or is this when the slow running fan light comes on?
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Re: cooling fans

Post by rutter123 »

yes on the stat housing there are 2 temp warning switches on the top, one is set at 102 deg the other at 112 deg i believe which i think is too high, i have removed the higher temp switch and replaced it with a radiator fan switch rated at 88 deg wired to the lamp.
i did a google search for the switch m14 x 1.25 thread 90 degree fan switch my local factors had one, i think its from a renault, i have the sender for the digi temp gauge where the lower temp switch was. so both the warning lamps of death are now redundant in favour of a temp gauge and 90 deg warning lamp.
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Re: cooling fans

Post by Thread Bear »

I tested my set up on the Estate turbo and it all works. I should not have said that after the last month of set backs!

From previous experience I always found that if the cooling on the 1.7 TD was requiring fans there had to be a reason. Towing, steep hill work etc. In other words heavy use of the turbo generates a lot of heat. Sat in traffic does not but reduces air flow. The rad on the 1.7 TD is big enough, in prime condition, to be pretty relaxed about this, where as some of the small versions might need the fans when stuck in traffic. In most cases of fan action on the 1.7 TD a look found a problem like low water, muck in the coolant, crap in the radiator matrix. So I can imagine a gentle driver getting caught out with defective fans as they have not come on in an age and fail the very time you need them. All the more reason for sensible information rather than a light telling you 'your engine is cooked' and another saying 'I told you so'. I like the idea of an idiot light telling me the fans are tripped despite having a temperature gauge.
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Re: cooling fans

Post by RobC »

I just did the test on the fan cut-in switch and found that the low temperature side of the U switch operates both fans at low speed, but the higher temperature side of the U operates just the nearside fan at high speed. The offside fan is stationary.

Does this mean something's wrong, or is that how it's meant to work? At a higher temperature with the nearside fan at high speed, would the offside fan continue to run at low speed because the water temperature was obviously still above that required for both to come on at low speed...?

If that makes sense ;)
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