Installing a diff cooler override switch and improving the automatic control system

[DJFarmo]

How to add a manual override switch for your diff cooler and make it activate based on oil temperature only, without cutting a single wire on your car

Recently I decided that it was time to change my diff oil. After a quick read around on this forum I discovered that several people had hot-wired their diff oil pumps in order to pump fresh oil into their diff casing, rather than feeding oil through the filler plug in the more conventional way. Also, in order to get as much of the old oil out as possible, it seemed to me like a reasonable idea to hot-wire the pump in order to purge the cooling loop when draining the diff oil.

I had a look in the workshop manual for info about how the diff cooler worked and I was surprised by what I found: when driving the diff oil cooler pump will only activate if the diff oil temperature is at or above 130c and the car is doing more than 75mph. Whilst I am sure Nissan had their reasons for this, I don’t see why the pump shouldn’t operate when the road speed is less than 75mph.

I therefore decided to install a manual switch in the cabin to act as an override. I started by looking at the diff cooler control system wiring diagram in the manual (page PD31) to work out how I could override the existing system whilst making the minimum of changes.

I should mention at this point that I don’t work with electrics and my knowledge in this field is pretty basic, so the wiring diagram seemed pretty complicated at first glance. However, I had a read through the ‘How to Read Wiring Diagrams’ section of the manual (pages GI9 to GI17) and it really helped explain what was being shown on page PD31.

After a bit of studying the diagram I came up with a very simple way to add a manual override switch for the diff cooler and remove the 75mph criteria so that the diff oil cooler will always come on when the oil temperature is above 130c, even if the override switch is ‘off’.

Here's what I ended up with (please excuse the mobile phone pics taken at night...):

Off:


On:



The Theory

The following diagram shows the two modifications that I wanted to make. The one shows what is required to add the manual override switch; the other shows the very simple short-circuit that will remove the 75mph criteria.



[Note: It should be possible to click on any of the pictures in this thread to give you the option to view a higher resolution version.]

These modifications use the existing relays to activate the oil cooler pump, rather than having to hard wire a new circuit directly to the pump.


Parts and tools

• A switch*
• About 6 meters of wire (One 5m length and two 40cm lengths)
• An assortment of spade crimp connectors
• A wood staple
• Wire cutters
• Wire strippers
• Crimping tool (I used mole grips…)
• Basic toolkit [Philips screw driver; 10mm socket, etc.]
• Claw pick-up/retrieval tool (helpful to have) [Like this: http://www.amazon.co.uk/600mm-FLEXIB.../dp/B00439FN06 or http://www.machinemart.co.uk/shop/pr...omotive-tools]

* I bought a switch off eBay to fit in the slot currently occupied by my “coin holder”, next to the front frog lights switch to act as the override switch. Here is a link to a similar switch:

http://cgi.ebay.co.uk/Off-Illuminate...item19be6a295d


Step by step guide


Step 1: Accessing the relays in the boot

Open the boot.
Remove the four screws that hold the CD changer in place; unplug and remove it.
Remove the relevant trim clips and pull back the boot lining on the right hand side of the boot to reveal the two diff oil cooler relays and the speed control amplifier.
Remove the three screws that fix the bracket supporting the relays to the car.

You should now have a situation that looks something like this:




Step 2 [Optional]: Testing to see if the oil cooler pump is seized

Before I started wiring up my manual override system, I thought it worth a moment to see whether my diff oil cooler pump was working, as it was unlikely to have ever come on in the 10 years since the car was made.

Testing is relatively straight forward, but does require jacking the back of the car up.

Firstly, unplug the speed control amplifier as such:



Then, jack the back of the car up. As you want to get to the back of the diff casing, the best jacking point to use is the diff casing itself, which the manual shows is a suitable place to raise the car:



Next, unplug the connector [T13 in the manual] shown in the picture below:



To test the diff oil pump, you need to switch the ignition on to position II and then make an earth connection to the metal terminal inside female harness connector. In theory, you should be able to connect it to the hard earthing point that sits about a foot away:



As soon as you make the connection, you should hear the pump fire up.

If you have trouble making an effective earth contact, I would recommend taking 2 minutes to attached one end of your long wire to the negative terminal of the battery, then running it under the car and attaching the other end to the metal terminal inside the female connector.

At this point, I was also curious to know whether the mythical diff oil temperature warning light on my car worked. I’d read about this light before on the forum, but as it does not flash up when you switch the ignition on, I wasn't sure whether it even worked.

To test it, all you need to do is unplug the connector shown in the picture below [T12 in the manual] and attach your earthed wire to the metal terminal inside the male connector you have just disconnected.



When you have done this, have a look on your dashboard and you should see this light:



Once you have verified that your diff pump (and hopefully your diff oil warning light) work, turn the ignition off, lower the car and reconnect the speed control amplifier.

[DJFarmo]

Step 3: Wiring the relays

Returning to the relays in the boot - we are firstly going to remove the 75mph constraint so that the diff oil cooler will come on automatically whenever the diff oil temperature hits 130c, irrespective of the car's road speed.

The following wiring diagram gives additional detail on how we are going to do this, as well as wire the override switch. The bottom of the diagram shows the connections we will be tapping into to achieve this.



Remove the connector from the base of the black relay [T15 in the manual] and fetch your wood staple.



Looking at the back of the connector, you need to insert the staple into the spade connectors on terminals 3 and 4 – terminal three has a yellow wire and terminal 4 has a white wire.



Press the staple in firmly so that it won’t drop out.



Finally, reinsert the connector back into the black relay.

You have now removed the 75mph constraint from the automatic diff oil cooler system! If you don’t have a staple or an alternative piece of metal, you could just disconnect the speed control amplifier and leave it disconnected – this will have the same effect.


Step 4: Wiring the override switch to the oil cooler relay

Remove the connector from the base of the blue relay [T14 in the manual].
Find a suitable spade connector that will fit snugly into the space where the white wire attaches into the back of the connector [contact # 2 of T14 in the manual]. I found that a medium size male connector worked great – when pushed firmly in it couldn’t be easily removed.

Strip one end of your long length of wire and attach the chosen spade connector.

Firmly press the attached spade connector into the terminal block and verify that it won’t just drop out once you re-mount the relay assembly. If necessary use a zip-tie to secure it.







Step 5: Routing the wire to the cabin

Unclip the gear stick trim surround.

Pop the fog light switch out and also remove the “coin holder” immediately behind it.

Pop out the electric mirror switch.

Remove the rear seats: Flip down the seat back, remove the 4 bolts holding it to the hinged bracket and remove from the vehicle. Then remove the plastic covers that obscure the brackets retaining the seat squab at the front, undo the 4 retaining bolts and remove from the car.

We now need to loosen the side trim panel on the driver’s side. Remove the necessary trim clips to be able to expose a small gap at the top as shown below:



Using your claw pick up tool, feed the wire you have attached to the oil cooler relay up through the top corner of the boot and into the cabin:



Then feed the wire down to it comes out of the bottom of the trim panel.



Next, open the centre armrest storage compartment, remove the two Philips screws and lift the trim panel slightly.

Place the end of the wire into the pick up tool and feed it under the carpet so that it emerges under the centre armrest trim.



Then route the wire under the centre trim panel to that it emerges out though the hole that was previously blanked off by the “coin holder” and pull through a length of slack.




Step 6: Wiring up the override switch

[Note: When I wired up my setup, I discovered that I needed a 12v supply from within the cabin to power the light on the switch. I only discovered this at the very end, after I had taken many of my wiring photos. Knowing what I know now, I will set out the best way to wire the switch. However, this will be slightly different to how I wired mine and as a result there aren't many photos I can show and in the photos I do show there may be some small differences between what I say should be done and what is shown. I will try to note these differences where possible.]

So far we have run a wire from the diff cooler relay into the cabin. To complete the circuit we need to tap into an earth connection so that we can then add the switch and control the oil cooler pump. Also, we need a 12v supply to power the light on the switch. The most convenient place to access an earth and a 12v supply is from the electric mirror switch:



Further down I show which lines you need to tap into photographically.

Take your new override switch and find three female spade connectors that connect firmly onto the male connectors on the base of the switch.
Attach one of these spade connectors to the end of the wire coming from the relay in the boot and the other two to both of the 40cm lengths of wire.

Look at the back of the connector that plugs into the base of the electric mirror switch. Find two spade connectors (I found that small female ones worked well) that fig snugly alongside the orange wire terminal and black wire terminal. Connect these spade connectors to the bare end on each of the 40cm wires so you have lead that look a bit like this:



Next, take one of the 40cm wires and firmly insert the spade connector you have just attached into the space alongside the orange wire terminal on the back of the mirror switch connector. This is your 12v supply.

Take the other wire and insert the relevant spade connector alongside the black wire terminal. This is your earth lead.





Make sure that both leads will stay attached to the connector – use a zip tie if necessary to help keep them in place.

To connect up the override switch, connect the lead from the boot to the terminal on the switch marked with a ‘+’ symbol within a circle:

Then connect the earth lead (attached to the black wire terminal on the mirror switch) to the other terminal on the same of the switch.



Finally, connect the 12v supply (attached to the orange wire terminal on the electric mirror switch) to the unmarked terminal on the other side of the switch.



Unfortunately I don;t have a picture of it all wired up correctly, but here's how it would look:



Turn the ignition on to position II and flick the switch – the light should come on. Walk around to the back of the car and listen to see if the pump comes on.

If it all works as planned, replace the rear trim panel, rear seats, reinstall the screws in the centre armrest storage box, replace the foglight, mirror and override switch, gear stick surround trim, reattach the relay bracket, boot liner and finally reconnect and reattach the CD changer.

Hopefully you should have something that looks like this:



You now have a temperature only automatic diff cooler with manual override!

[DJFarmo]

[Extra space]

[skinz180189]

None of the images work for me mate.

[DJFarmo]

None of the images work for me mate.

Thanks for letting me know. Hopefully this is now resolved.

[al.]

this has been covered before mate, but i think your guide is a bit more noob friendly. i did mine about a year ago, very simple mod that can prolong the life of your diff, especially if you're doing drifto or trackdays - it's worth noting the cooler, pump, and pipework can get filled up with a fair percentage of the oil in the casing when you activate it (it's probably never been on before...) so top up the diff oil after you've run it for a bit.

oh and the earth strap to the rear diff mount is often broken (one of the reasons the pump never comes on) so check/renew that at the same time

[DJFarmo]

this has been covered before mate, but i think your guide is a bit more noob friendly. i did mine about a year ago, very simple mod that can prolong the life of your diff, especially if you're doing drifto or trackdays - it's worth noting the cooler, pump, and pipework can get filled up with a fair percentage of the oil in the casing when you activate it (it's probably never been on before...) so top up the diff oil after you've run it for a bit.

oh and the earth strap to the rear diff mount is often broken (one of the reasons the pump never comes on) so check/renew that at the same time

Damn it. And there was me thinking I'd come up with something original!

Anyway, hopefully my guide will make it possible for anyone who hates wiring/electrics.

[voodoo_melon]

Does your diff cooler ever actually start up now then?

[DJFarmo]

Does your diff cooler ever actually start up now then?

Do you mean automatically, now that the 75mph requirement has been removed?

I wouldn't be able to hear the pump come on automatically as it is very quiet and can't be heard when driving. If you did want to know whenever the pump was working you could always hook up an LED in the cabin.

[voodoo_melon]

I thought the light came on when it was over temperature? If not, what's that light for?

[Jonnay]

think I'll give this a go at the weekend Nice post, thanks!

[DJFarmo]

I thought the light came on when it was over temperature? If not, what's that light for?

So the cooler should come on automatically at 130c, but if you are driving it like a D1 drifter and the temperature hits 180c then the light on the dash will come on too.

[VIDAL BABBOON]

Is it an issue then ?

[al.]

imo not in a road car. in a drift car with an expensive 2 way every bit of cooling will help...and on top of that the ep additives in the oil degrade with temperature

[VIDAL BABBOON]

I have never seen the diff light come on and i have tested it on more than one occasion, and it's done a fair amount of track work.