Guide: Lowering engine fan kick in temperature

[Niall]

Im sure most GTi owners hate this time of year due to the chronically hot engine temperatures. Ive never seen one cook its self because of this (except when the engine fans have failed) but i know a lot of owners unplug the brown coolant sensor so that the fans default to high speed. Issues with this can be over cooling (which can do just as much damage as over heating!) and premature wear on the fans not to mention that god awful noise all the time!
So, simple solution. Lower the kick in temp. On the gti, low speed comes in at 87 and high speed at 97 i believe. With this simple mod, you can set (to an extent) where the high speed fan kicks in

Locate the brown coolant temperature plug. Its located on the theromstat housing (right hand side of the block) between the green and blue sensors. There are two yellow wires running into this and we need to find out which the supply is. Grab a multimeter and find which wire has voltage running down it (should be about 4.5-5v).

Once you have found the wire, cut it and extend the wires to where you want the switch (no need to have it in the cabin really. Once its set, you may as well leave it) and solder a variable resistor on the end of the wires.

   

Next, mount your switch, tidy everything up and make sure you heatshrink all your wires to protect from water ingress.

   

Now its time to set it up. I suggest running the car upto the temp you want the fan to kick in (mines at about 95 degrees) and turn the knob (giggidy) slowly until the fan kicks in. Take it for a drive to try and drop the temp back down to normal driving temp and make sure the fans turn off. Normally they will turn off at about 7-10 degrees lower than kick in point so make sure you dont set it too low that it cant drop the temperature down low enough to switch them off

[Grant]

Serious observation, no trolling.

How will leaving the fans on cause over cooling, in comparison to the airflow of doing 70-80mph on the motorway?

[Niall]

Serious observation, no trolling.

How will leaving the fans on cause over cooling, in comparison to the airflow of doing 70-80mph on the motorway?

Tbh it only happened on mine due to a sticky thermostat but during town driving, it will never heat up enough. Dont forget, the fans arent just cooling the radiator. There is also a fair bit of heat being carried away from the external faces of the engine when the fans are on full chat. Mine had been down to 60 degrees stable during the winter which is far too cold!

[Grant]

But the point I am making is, you say having them going full chat can cause it to run too cool. Surely more air displacement is caused from driving at 70mph. With a properly functional thermostat, leaving the fans on constantly shouldn't make a difference? In terms of running too cold that is..

[Niall]

But the point I am making is, you say having them going full chat can cause it to run too cool. Surely more air displacement is caused from driving at 70mph. With a properly functional thermostat, leaving the fans on constantly shouldn't make a difference? In terms of running too cold that is..

Well as i said, i dont know the full physics of it but i know with mine, it sat at a steady 60 during the winter with the fans on full chat. plug them back in and it was at 75 which is still a bit low (due to the thermostat) but much better.

[Dum-Dum]

What resistence do you need to drop for every degree.

[Niall]

Dunno. Hence why using a variable resistor lol. Tbh it was a bit of a rushed job but tomorrow ill go out with PP and a multimeter and work it out for every 10 degrees and post up here

[Niall]

Guys just to update on this, ive run this setup for a month now and can confirm the temp hasnt gone over 85 once including sitting in heavy traffic on the way to ace on monday. Ive also confirmed its reading correctly several times with PP.
I did have a slight issue where if i brought the fans on any lower (wouldnt want to anyway), it would bring up the stop light and they would go to high speed as a fail safe. Tomorrow i will measure the resistance i have mine set at so you can go and buy resistors to do this. Tbh there is no need for a variable pot as it wont need adjusting

Im also happy to do this for people at meets as its only a 2 minute job

[vlj]

Do you know of a way you can do this for mine without the middle plug - as I said to you, it's blanked off!

[Just Sean]

Im also happy to do this for people at meets as its only a 2 minute job

sweet! Need to see you soon anyway xx

[Niall]

Do you know of a way you can do this for mine without the middle plug - as I said to you, it's blanked off!

Therotically it will be exactly the same but from the sensor on the rad but let me check that they give the same resistances for temps and ill work something out for you

Im also happy to do this for people at meets as its only a 2 minute job

sweet! Need to see you soon anyway xx

Yeah we need to meet up soon! Ill be at CC so will bring a bunch of resistors with me. Work kindly gave me a box of a few thousand that im sure i can take 1 or 2 lol

[Iceman299]

But the point I am making is, you say having them going full chat can cause it to run too cool. Surely more air displacement is caused from driving at 70mph. With a properly functional thermostat, leaving the fans on constantly shouldn't make a difference? In terms of running too cold that is..

Im guessing driving at 70mph keeps the engine hotter than down driving at 20mph