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How to fit thermo fan bypass switch

Immortality

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This topic has come up in a few threads lately so i though i'd do a how to.

you need:
1 x switch
1 x wire, .5mm2 will be sufficient in size, couple of meters depending on where you locate the switch.
1 x heatshrink (substitute electrical tape if not avail)

basic hand tools: wire cutters, wire stripper, soldering iron etc.

method

1. disconnect the battery negative terminal

2.first you need to decide where you are going to mount your switch, i've mounted mine next to the gear stick (pic 1)

3. remove the passenger side kick panel and locate the wire for the thermo fan relay that comes from the ecu (pic 2), it's a blue wire with a white trace, i suggest unwrapping the wiring loom a little to give yourself more wire to work with

4. you need to splice your bypass switch wire to this blue/white wire(pic 3). there are a couple of ways to do this but i suggest that the best way to do this is to solder it as it's a low current circuit and we need a good connection. i cut the wire and stripped each back about 8mm, then i stripped the bypass wire about 20mm. tin each stripped end slip the heatshrink over one of the wires. i then soldered the bypass wire and wire coming from the loom together and then soldered the wire coming from the ecu to that. then it's a matter of slipping the heatshrink down over the joint and applying some heat. if you don't have heatshrink available then i suggest that you don't cut the blue/white wire, just carefully strip some of the insulation off and solder your bypass wire there, then insulate with electrical tape.

5. pull your wire to your choosen location for your switch, mount and wire the switch.

6. then you need to connect the second side of the switch to an earth point. one possibility is the use the earth side of the sig lighter. i choose to use a screw mounting a panel to the chassis near the ecu(you need to make sure that it's a good earth point).

7. cleanup and secure all the new wiring, re-wrap the wiring loom if you unwrapped it etc.

8. re-connect the battery negative terminal and test, you should be able to turn the key to the 'on' position and be able to switch the thermo fan on with the bypass switch. run engine up to temp to make sure the ecu is still switching thermo fan on.


if your really keen then you can also mount an LED somewhere and wire in series with the new switch, that way you will also have an indicator to tell you that you have the bypass switch on.

there is also a basic wiring diagram attached.

Edit: I've attached the wiring diagram for the VT V6 Commodore. From VT onward the PCM switched the high speed thermo fan and the low speed thermofan is switched from the BCM. For best effect this mod should be wired into the high speed relay fan using the Blue wire with white trace (BLU/W) from pin F6 on the PCM (as per the wiring diagram 5a bellow).


happy wiring:thumbsup:
 

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Last edited:

Morton

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That's so simple, easy to follow, and with some excellent pictures. You bloody champion - I think I know what I'm doing this weekend ;)
 

steveo

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so does this just help keep the motor cooler? like a lower temperature thermostat?

is it bad to keep thermos on the whole time?

does it affect the ecu turning on the fans?

worth doing to a vx?
 

Morton

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1) It helps cool down the water in the radiator when your car isn't moving

2) yeah, you'll wear out the motor sooner. They have no effect over around 40kph anyway

3) not really... in fact, the switch here bypasses the ECU altogether

4) probably not, unless you have cooling issues. And then, I'd be looking at the thermostat and radiator first.
 

Immortality

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so does this just help keep the motor cooler? like a lower temperature thermostat?

is it bad to keep thermos on the whole time?

does it affect the ecu turning on the fans?

worth doing to a vx?

on the VN/VP series commodores the ecu doesn't switch the thermo fan on untill the coolant temp reaches 101 degrees C. i'd imagine the later models are the same. now thats fairly hot, if you run a cooler thermostat like i do it seems like forever before the thermo kicks in. my thermostat opens fully at 81 degrees (standard is about 91 degrees i think) cause i want to run it cooler so i want the thermo fan coming on earlier also.

the simple solution is to fit a thermofan bypass switch. the long term solution would be to get the memcal reprogrammed to bring the thermo fan on earlier to suit the cooler thermostat:thumbsup:

as morton said, above 40km/h the fan doesn't do anything cause the natural airflow through the radiator is greater then what the thermo fan can pull anyways. it won't effect the ECU at all. keeping the thermo fan on all the time could burn out the motor i guess but it hasn't happened to me yet and i've forgotten to turn it off once or twice after being stuck in traffic for a long time
 

Morton

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Aye, I leave my fan on sometimes without thinking about it :p I really need to wire up an LED in series with the relay to come on when my fan is. An idiot light on the dash somewhere... maybe even one on top of my temp gauge... like a shift light for my thermo fan :D hahahahaha...

ahhhh.... my work here is done.
 

Bz Kn33z

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Should just get a Switch with a LED built into it and locate it where you will see it more lol.
 

Immortality

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Should just get a Switch with a LED built into it and locate it where you will see it more lol.

i did have a switch with a built in LED unfortunatly i damaged it but i've also decided an LED in a different location would work better for me

How do you go about it on a VT.
Is the wiring the same when it comes to the fan relays ect.
If i follow this write up will it work??

the wiring would be similar. i believe the VT's possibly had 2speed thermos but don't quote me on this. if they do then there would be two outputs from the ECM for the different speeds. unfortunatly i have no idea about VT wiring as i've not play'd with one before. possibly try this web site Rob's Creative Calibrations it has wiring diagrams for VN to VT. (just had a quick look and it does have multiple speed twin fans by the looks of things)

you should be able to figure out what the wiring is from that, it has ECM pin outs etc so you can figure out which wire you need to interupt to manually swithcthe fans on. other then that the setup would be the same.

good luck and let us know how you get on:thumbsup:
 
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