How to fit thermo fan bypass switch

[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.

 

[HoldenManDan]

So if you were to use the Jaycar Electronics frequency switch so you could manually switch the fan on and get this mod to turn the fan off after say 55km/h, how would you go about wiring that up? In a VS that is (just switching on low speed fan would be fine)

Cheers

 

[Immortality]

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.

yes, the temp at the bottom hose will change with speed, but then the thermostat is there to maintian engine temp so will reduce flow to maintain that engine temp so i really don't see the point. then again how many car manufacturers have used wind tunnels or fluid dynamics in the past to design there radiators (and remember where talking about VN-VR commodores here which are based on a late 1970's basic chassis(VB commodore) and not modified much except maybe the front bar design till they reached the VT commodore) not many i'd say unless you were in the supercar business. i'll put it this way, my VH V8 has a stuffed thermo clutch mechanical fan and it was like that for quiet some time. i have a link electrosystems ECU on it (its a 308 with efi) which gives me a exact temp readout on a hand controller. it didn't matter if i was driving at 60km/h, 100km/h or 200km/h it didn't overheat, it only got warm when stuck in traffic. it has a 82 degree thermostat and sat with a degree or 2 of that at all times unless stationary.

from this i can deduct that 1. the cooling system was more then adequate for what it was intended. 2. the thermostat was working properly. 3. even driving at legal road speeds, in traffic, there was enough airflow through the radiator to keep it at it's operating temp

lets look at this another way, how much air does a good thermofan setup flow, my 16" davies craig fan is rated at 2100cfm ( from memory, can confirm later) so a good twin setup may flow 2500cfm (seeing as they use 2 smaller fans) or a really efficient setup upto 3000cfm. now lets say your commy is travelling at 50km/h (that equates to 2733.3ft/min) and your radiator measures 1.77ft x 1.34ft surface area or 2.37 sqaure ft. so at 50km/h (2733.3 ft/min) you have 2.37 x 2733.3 = 6477cfm airflow through the radiator. now lets assume that all that stuff (front bar etc) in front of the radaitor reduces that flow by half, then you still have 3238cfm airflow through the radiator at 50km/h.............


car manufacturers got rid of fixed mechanical fan cause they are a drain on power (fuel efficiency) and just aren't required at normal driving speeds, they progressed through thermoclutch mechanical fans to electrical thermofans cause they give more control. quiet frankly, if the cooling system on your car can't keep temps under control at normal road speeds then there is something wrong and using a thermofan thats running 100% is just masking the problem

 

[Immortality]

So if you were to use the Jaycar Electronics frequency switch so you could manually switch the fan on and get this mod to turn the fan off after say 55km/h, how would you go about wiring that up? In a VS that is (just switching on low speed fan would be fine)

Cheers

not familair with this particular kit from jaycar, i'll have little look later and see what i can figure out

 

[commsirac]

yes, the temp at the bottom hose will change with speed, but then the thermostat is there to maintian engine temp so will reduce flow to maintain that engine temp so i really don't see the point. then again how many car manufacturers have used wind tunnels or fluid dynamics in the past to design there radiators

Okay, Ill explain the point for you.

At the moment you have no actual way of measuring whether switching your fans on or off actually cools down the radiator at speeds of 40km/h or not. You appear to be basing your conclusions(that fans do nothing above 40km/h) on the fact that the vehicles you have driven dont need any supplementary cooling at speeds >60kmh, which is a perfectly likely observation, however, it cant be correctly deduced from that the fans dont do anything if they are used.....all you have established is that ram air is sufficient to keep your vehicles at thermostat temp at cruise.

Lets say at 60kmh on a level road at 25C that you are cruising at your thermostat temp of 82C without the fans on. If you switch the fans on you will see your temp gauge stay in the same place because the system cant drop any lower than thermostat temperature(unless super cooling goes on in the radiator).Its unlikely that you will experience ambient temps where your system will rise above thermostat temperature at cruise so this is why you need to do this test to be able to prove to yourself what effect running the fan has.

If you have a sensor at the bottom of the radiator it will give you an indication of how much cooling is actually going on.
For example,the temp while cruising at 60km/h at the bottom of the radiator maybe at 50C or so.
If as you claim the electric fans wont make any difference to airflow through the radiator, then when you switch them on the bottom of the radiator will stay at 50C, Im suggesting it will drop below 50C(or whatever it was at) when you switch on the fans. You can then be the judge of if they do anything for yourself. Hope that makes sense.

GM didnt use wind tunnels?, bet your life they did, especially with the VN to get flow under the bonnet just right to be able to make sure that it would be able to survive with just electric fans. I could make comment on the rest that you have written, however, the best thing would be for you to actually do as I have suggested as I believe (given your responses so far) that only hard evidence, that you can see for yourself, will make any impression on you.

I have actually done exactly what I have proposed to clarify some cooling issues I was having with a car............and the results didnt surprise me, just went against every bit of rhetoric I had heard from "radiator experts" etc.
A thermocouple is easy to poke into the bottom hose/radiator connection and hooked up to an appropriate multimeter can get you at least 1C accuracy on what is going on.

 

[Immortality]

Okay, Ill explain the point for you.

At the moment you have no actual way of measuring whether switching your fans on or off actually cools down the radiator at speeds of 40km/h or not. You appear to be basing your conclusions(that fans do nothing above 40km/h) on the fact that the vehicles you have driven dont need any supplementary cooling at speeds >60kmh, which is a perfectly likely observation, however, it cant be correctly deduced from that the fans dont do anything if they are used.....all you have established is that ram air is sufficient to keep your vehicles at thermostat temp at cruise.

Lets say at 60kmh on a level road at 25C that you are cruising at your thermostat temp of 82C without the fans on. If you switch the fans on you will see your temp gauge stay in the same place because the system cant drop any lower than thermostat temperature(unless super cooling goes on in the radiator).Its unlikely that you will experience ambient temps where your system will rise above thermostat temperature at cruise so this is why you need to do this test to be able to prove to yourself what effect running the fan has.

If you have a sensor at the bottom of the radiator it will give you an indication of how much cooling is actually going on.
For example,the temp while cruising at 60km/h at the bottom of the radiator maybe at 50C or so.
If as you claim the electric fans wont make any difference to airflow through the radiator, then when you switch them on the bottom of the radiator will stay at 50C, Im suggesting it will drop below 50C(or whatever it was at) when you switch on the fans. You can then be the judge of if they do anything for yourself. Hope that makes sense.

GM didnt use wind tunnels?, bet your life they did, especially with the VN to get flow under the bonnet just right to be able to make sure that it would be able to survive with just electric fans. I could make comment on the rest that you have written, however, the best thing would be for you to actually do as I have suggested as I believe (given your responses so far) that only hard evidence, that you can see for yourself, will make any impression on you.

I have actually done exactly what I have proposed to clarify some cooling issues I was having with a car............and the results didnt surprise me, just went against every bit of rhetoric I had heard from "radiator experts" etc.
A thermocouple is easy to poke into the bottom hose/radiator connection and hooked up to an appropriate multimeter can get you at least 1C accuracy on what is going on.

if you wanna go to the trouble of doing said test then be my guest, please post the results if you wish. i'm quiet happy with my setup as is. soon i will be able to burn my own tunes so will reset my thermostat on and off temps to suit my cooler thermostat. i personally beleive that i don't need my thermofan on when traveling around 50km/h cause natural airflow is more then sufficient to keep her cool and so far i haven't had any cooling issues, even when i left my thermofan disconnected for 2 weeks after i had the radiator out. so whether or not the thermofan has any cooling ability when traveling at 40+km/h is debatable and if you wish to prove me incorrect then i'll except any proof but is the thermofan required at those speeds to keep an engine at operating temp then the answer is no, even with a cooler thermostat then normal (as i have proven when i left the thermofan disconnected for 2 weeks without having overheating problems when traveling at normal speeds and having to stop at traffic lights etc)