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1995-2002 Range Rover P38A
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Discussion Starter #1
Hi all
Trying to upgrade the cooling system on a 1999 2.5 diesel. Last year the auto gearbox overheated while pulling a a large caravan. Searched the forum and RAVE and came up with a simple plan. Sourced a second hand fan as per the V8 spec (it actually came off a a diesel). Sourced a temperature switch from Island 4x4 (part no STC 4330 based on info on the Forum) and wired everything up through a 4 pin relay exactly as described in RAVE. Everything works fine (only one error - got the wires the wrong way round on the fan - it sucked instead of blow)

The only problem is that the fan switches on immediately it gets power through the fuse. Double checked the circuit and find that the "temp switch" is closed even at room temperature ( checked with multimeter). RAVE shows that the switch should be open. Have I missed something? Have I got the wrong part? Is the part faulty??

The wiring is as follows
Battery --- Fuse(30A)--- Relay pimn30 Relay pin 87--- Fan---- Earth
Battery --- Relay pin 86 Relay pin 85 ---Temp switch ---- Earth
Any help would be appreciated!! Cheers Mike
 

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This has come up before, the switch operates the opposite way round to how you expect. It's closed when cold but goes open circuit when it gets hot. Suspect it's a fail safe so if it, or the wiring to it, get damaged the fan runs all the time.
 

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1995-2002 Range Rover P38A
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You need to use a change over relay and it should be all good.
 

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Discussion Starter #4
Thanks for your replies. I assume Dtoyne that by change over relay you mean the five pin relay???? If so I have one or two. Do you have any idea how to wire the relay into the fan circuit??? Thanks Mike
 

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It is a few years since I messed with my gearbox cooler, but if I remember correctly there is +12v power to the fan motor all the time. Just like the aircon fans.
The -ve connection from the fan completes the circuit via the temperature sensor switch to earth.
 

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Assuming the switch works the wrong way round, you want ignition switched supply, via a fuse, to pins 85 and 30 of the relay, pin 86 to the switch with the other side of the switch to ground. Pin 87a to the fan and the other side of the fan to ground. That way the relay will operate as soon as you switch on the ignition and the fan will run when the switch opens and the relay releases.
 

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Just for info.
At what temperature does it open?
 

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I don't know where I got it from but I made a few notes at the time. Gearbox overheat warning & fan ON at 120-130 deg C and OFF at 82-88 deg C.

I can verify the ON setting is correct at least as I have fitted a temperature probe to the gearbox sump.
The gearbox does run hot when towing and the warning does come on at that sort of temperature.
 

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Discussion Starter #9
Thanks once again for all your replies. This one of the best forums I have used for getting USEFUL replies.

I had a 5 pin relay so experimented on the bench and it's good to have it confirmed by Richard that I had it right before trying it on the car. On the temperature side, I found somewhere in RAVE that the fan switches on at 95 degrees, but usual with RAVE I can't find it - but still looking. Thanks again for all your responses, they are most appreciated.
Cheers, Mike
 

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I wasn't able to find any mention of the diesel auto gearbox cooler fan in RAVE but I suppose it must be in there somewhere. If you want a forum that gives usdeful replies, you want to try the one that Dave and I are usually found on, far better than here.......
 

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Discussion Starter #11
Thanks for trying Richard. I went through just about every possible section in RAVE. The only mention of the fan and switch is in the circuit diagram section under diesel(!!!???) Find that RAVE is a typical land rover product, when using it nothing is ever straight forward!!. By the way to all those that asked - the switch for the gearbox warning light is set at 120-130 degrees ( RAVE auto box section) the switch for the fan set 95 degrees +/- 3 ( Electrical trouble shooter section under auto box) Couldn't be easier to find?????
Cheers Mike (PS will look for you on the other forum)
 

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Discussion Starter #13
For kapilamuni, I searched everywhere I could think of for an alternative thermostat switch that was compatible with 12 v systems and failed. Even looked at the option of fitting a screw-in-type from another vehicle but there was no where to fit one in the system that would not cause further problems. Adaptors could be used but by the time you were done they were more expensive than fitting OEM!! Cheers Mike
 

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I used this switch to ground the relay pin 85 for the oil cooler fan on my Porsche.
ACDelco D-1879 Engine Coolant Temperature Switch
They are available on eBay. If I remember correctly there is a little screw to adjust the temp.

this is other parts I used:



 

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oh and a little more info...The Delco part number is: D1879, the GM part number is 25036512.
Be sure to turn the adjustment set screw about 1 and 1/2 turns clockwise to lower the cut-in temp to about 180 deg F.
(Don't go crazy on this screw or might loose it as it falls into the switch body).
 
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