How to fit thermo fan bypass switch

[immortality]

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.

happy wiring

[Matt_vp]

good write up mate

[Morton]

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]

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]

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]

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

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]

Aye, I leave my fan on sometimes without thinking about it 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 hahahahaha...

ahhhh.... my work here is done.

[Bz Kn33z]

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

[chevy_big_block_bro]

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??

[immortality]

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

[chevy_big_block_bro]

The VT has 2 speed thermo's but the high speed has a blue/white wire from the ECU.

Ill earth it out tomorrow and see what happens

[nick88]

doesnt the vs have a low/hi speed fan aswell? i think depending on the temp it either spins 'slower' or 'faster'??
correct me if im wrong tho...
Nick

[immortality]

doesnt the vs have a low/hi speed fan aswell? i think depending on the temp it either spins 'slower' or 'faster'??
correct me if im wrong tho...
Nick

yep, again, check the site above for info on the wiring.

[savage1987]

I think that's the same with the VN V6 too - fan comes on low speed if you put the air con on, high speed if it's getting hot. Can't remember where I read that...

[immortality]

I think that's the same with the VN V6 too - fan comes on low speed if you put the air con on, high speed if it's getting hot. Can't remember where I read that...

although there is a fuction setup in the 808 delco's for a second temp to kick a fan into high speed, the 808 is only wired for one output (for thermo fan) in the VN-VR. so unfortuntly it's a one speed setup only. if it was a two speed setup there would need to be 2 relays to switch the power supplies for the different speeds on the fan. in the VN-VR V6 the thermo fan is switched on for the A/C (it's the same output and circuit). for the VN-VR V8's it still switches the same output on the ecu and uses the same circuit as the V6 setup although instead of having a large thermo fan there is an auxillary fan just for the A/C. it would be fairly simple to convert the V8's to an electric thermo fan setup as all the wiring is there(it's just used for the A/C fan which you could remove if you had an electric thermo fan), you would just need to get the tune modified (memcal) to have it switching the thermo on and off at the appropriate temps etc

[savage1987]

Oh ok. My mistake

[Cheap6]

I think that the ECM does switch the auxilliary electric fan on the VN-VR V8 in response to high(er) engine temperatures so it might be used to directly control a thermo fan if swapped, without a rewritten MemCal if the temperature that it switches at is low enough.

For a thermo fan swap on a V8 or to alter the switch on point of the V6 fan this:

Jaycar Electronics

with the input voltage taken from the coolant temp sensor and wired instead of a manually operated switch would allow whatever switch on temperature is desired. Using it to switch in and out this:

Jaycar Electronics

would allow two speed fan control.

If you want to cut the fan out above a certain road speed, use this:

Jaycar Electronics

with a speed sensor signal.

(No, I don't own shares in Jaycar).

[immortality]

I think that the ECM does switch the auxilliary electric fan on the VN-VR V8 in response to high(er) engine temperatures so it might be used to directly control a thermo fan if swapped, without a rewritten MemCal if the temperature that it switches at is low enough.

i haven't personally tested this theory on a V8, however i have checked the standard V8 memcal which has the same temp settings as the V6(for thermo cooling fan). as both the thermo fan setup for the V6 and aux A/C fan for the V8 use the same circuit from the ecm one could possibly assume that if you were to wire a V8 with thermo fans into the A/C circuit that they would work. (you could probably remove the A/C fan if using thermo fans to cool engine as they are much more efficient then any little A/C fan)

however to test you would possibly need dissable the viscous coupling fan temporarily to check that the A/C fan does come on with elevated engine temps.

you could use an external type controller to change the temps that the thermos activate however there isn't much point unless you run a cooler thermostat otherwise the thermos would be on a lot of the time when there not really required. in the memcal the thermo won't run when the vehicle is moving faster then 40kph because the natural airflow through the radiator is greater then what the thermofan can pull through the radiator, this however is a problem for people entering burnout comps because the vehicle is stationary but the ecm thinks it's moving and doesn't require the thermofan to cool the engine. for those with the ability to alter there own tunes they can set there thermofan on and off temps to suit the thermostat that they run.

i have considered wiring the bypass switch into the relay circuit for the line locker so when doing burnouts i won't have to manually switch the thermo fan on (when i get around to fitting the line locker that i've had sitting in the garage for 6 months)

if i get a chance i may try and test this theory on a mates VN V8 that he's currently fixing from frontal impact damage. if we can confirm this works it would definitly simplify this conversion for others in the future

[Cheap6]

i haven't personally tested this theory on a V8, however i have checked the standard V8 memcal which has the same temp settings as the V6 (for thermo cooling fan). As both the thermo fan setup for the V6 and aux A/C fan for the V8 use the same circuit from the ecm one could possibly assume that if you were to wire a V8 with thermo fans into the A/C circuit that they would work.

The V8 runs cooler than the V6 (witness the radiator cap pressure ratings for each), so the switch on point may be too high for the V8 if it is the same in both. What I would like to see if setting up a V8 to run thermo fans would be the normal operating temps under a variety of conditions, with a factory set up, and then match that by setting the thermo fan switch on point or points. Access to a datalogger would help in this; a cable and Winaldl (or similar) would do.

(you could probably remove the A/C fan if using thermo fans to cool engine as they are much more efficient then any little A/C fan)

It may even be better to remove the small fan to help the flow through two bigger fans (Ford/VT/whatever) because the small fan may disturb the airflow through them.

however to test you would possibly need dissable the viscous coupling fan temporarily to check that the A/C fan does come on with elevated engine temps.

Temporarily blocking the radiator with, say, cardboard will work. As will using a spare (wrecker) coolant temp. sensor plugged in and heated. Or, applying a variable voltage potential to the sensor plug or a variable resistance across it.

you could use an external type controller to change the temps that the thermos activate however there isn't much point unless you run a cooler thermostat otherwise the thermos would be on a lot of the time when there not really required.

Or using electric fans on a V8 with the ECM controlled relay being switched at too high a temp.

for those with the ability to alter there own tunes they can set there thermofan on and off temps to suit the thermostat that they run.

That is the neatest way to do it but requires skill/knowledge and the appropriate equipment (or a favour from, or remuneration to, someone who does). ~$65 plus an hour or two of assembly for the kits may be easier/cheaper.

The line locker switch idea is good. Perhaps a latching relay, triggered manually by a momentary switch, with the latching relay disabled by a frequency switch over a set speed would also work.

[immortality]

The V8 runs cooler than the V6 (witness the radiator cap pressure ratings for each), so the switch on point may be too high for the V8 if it is the same in both. What I would like to see if setting up a V8 to run thermo fans would be the normal operating temps under a variety of conditions, with a factory set up, and then match that by setting the thermo fan switch on point or points. Access to a datalogger would help in this; a cable and Winaldl (or similar) would do.

having just checked the standard trident thermostats,

V6 = 195degrees F (90.6 degrees C)
V8 = 190degrees F (87.8 degrees C)

optional cooler thermostat, 180degrees F (82 degrees C)

have just checked the standard settings

V6
on temp = 101.75 degrees C
off temp = 98.75 degrees C

V8
on temp = 107 degrees C
off temp = 101 degrees C

VN-VR only run single speed thermo fan although there is provision in the tune for 2 fan settings (2 speed thermo's) however there is no extra wiring in the loom that i am aware off to use this extra function

VS onwards do use a 2 speed thermo fan setup on the V6 (unsure about the V8 models as i haven't really ever looked at there wiring diagrams to compare to the V6 wiring loom)

so if you were to use the factory circuit from the ECM you would either want to have the memcal altered to switch on at lower temps or use an aftermarket controller.

no doubt Dr bob would alter a memcal to suit for a small fee but then why not spend a little extra and get a tune done by Dr bob also

[Cheap6]

For VN-VR, I found the same on/off temperatures too. Also, the fans are switched on at those temperatures regardless of road speed. With the A/C on and the temp. below the switch on points, the fans are switched off over 55km/h.

VT uses a two speed fan with two sets of windings in each motor = 4 wires per fan. One set of windings is powered for low speed fan operation, both are powered for high speed. The low speed windings are powered by the PCM via the BCM, the high speed directly by the PCM.

The switch on criteria for the VT fans are:

V6 Low speed:

On, >: 104C
Off, <: 99C
On with ignition off if > 117C
On with A/C pressure > 1550 kPa
Off with A/C pressure < 1170 kPa and speed > 50 km/h

V6 high speed:

On, >: 112C
Off, <: 108C
On with A/C pressure > 2600 kPa
Off with A/C pressure < 2300 kPa

V8 low speed:

On, >: 95C
Off, <: 90C
On with ignition off if > ????
On with A/C pressure > 1550 kPa
Off with A/C pressure <1170 kPa and speed > 50 km/h

V8 high speed:

On, >: 104C
Off, <: 99C
On with A/C pressure > 2600 kPa
Off with A/C pressure < 2300 kPa

To switch VT fans manually (in a VT), you would need to wire a parallel earth switch, as described here by immortality for the VN-VR V6's, to the blue/white wire, pin F6 in the PCM, which will trigger both high and low speed windings or one to the orange/black wire to pin B7 in the BCM to power just the low windings.

[Cheap6]

does it affect the ecu turning on the fans?

Nope. VL Walkinshaw and JD/JE Camiras (and perhaps LD Astra/N13 Pulsar) use this method to switch on the fan with the A/C on (with the medium pressure switch on the receiver drier).

[commsirac]

Temporarily blocking the radiator with, say, cardboard will work. As will using a spare (wrecker) coolant temp. sensor plugged in and heated. Or, applying a variable voltage potential to the sensor plug or a variable resistance across it..

It can be quite difficult on a cold day to try and block off the radiator with cardboard etc to get it hot enough with a clutch fan which even with the slightest of gaps will pull enough air to keep the rad cool. One trick Ive found useful is to wrap a heavy duty garbage bag around the fan.....taping it on so it wont foul anything.
Electric fans:
There are quite a few myths that appear to have become fact simply through hearsay:
They obstruct airflow if on at speeds greater than 60km/h.....
Dont do anything if used above speeds of 40km/h....

[immortality]

Electric fans:
There are quite a few myths that appear to have become fact simply through hearsay:
They obstruct airflow if on at speeds greater than 60km/h.....
Dont do anything if used above speeds of 40km/h....

the A/C auxillary fan is mounted in front of the radiator there for it would obstruct the airflow over the part of the radiator that it covers. having also spoken to a few radiator places about thermo fan setups they have suggested that the thermos should be mounted behind the radiator to "pull" the air through rather then in front of the radiator to "push" the air through.

it figures that at a certain speed the thermofan becomes redudnant because the natural airflow through the radiator is greater then what the thermofan can pull through the radiator, look at the V8 supercars for example, they don't even run a thermofan, they just gotta make sure that they don't sit still for to long otherwise they have overheating problems but once they move off from the start they don't have any issues at all.

i run a 180 degree F thermostat in my VN, if i pull up at the lights and it's at it's normal operating temp then it takes a few minutes before the thermos kick, most times unless i'm stuck in traffic my thermofan never comes on

[commsirac]

Immortality, try putting a temp sensor in the bottom of your radiator(yes the bottom so you can drive the car at thermostat temp) and drive with the fans on and off. You should find a significant difference in temp at 60km/h and even at 100km/h, the absolute difference will be greater as the ambient increases. This is also assuming you have the standard commodore fan(s) on full. True the difference will get smaller as you go faster, but blanket statements like fans dont do anything over 40km/h are only true for puny fans.
Radiator places are the last place Id go for advice on fans and airflow......with all due respect they arent set up with wind tunnels nor do any of them appear qualified in subjects such as fluid dynamics....
I dont want to get into a great discussion about people's theories here.....do your own tests and get some real data so you can get a feel for what is going on.