anyone fitted a radiator fan switch?

[Simon Baxter]

I don't get why you need to fit a switch, it's "fixing" something that isn't broken.
If all the parts of the system are working as they should then there is absolutley no problem with the system.
This is the UK, remember, VW used the same cooling system for here as they did for Africa (a bit warmer than sodding chipbury!) and places like Arizona, Australia...
Rather than fit an extra switch you would be better spending your time/money on making good the automatic system that VW spent £££ developing.
I have yet to see an instance where a override switch has been a necessity.
I've also never seen a van here with a single speed fan.
The first stage is usually all thats needed here, I think I have only ever heard the second stage work on anything once, and that was my own mTDI when the headgasket went and it got seriously hot on the motorway, no switches would of helped prevent that!!

Seriously, tell me why you need an override switch?

[Mocki]

a very rare thing has occured........
i agree with simon....lol!

[tencentlife]

Can anyone recall if it is possible to simply connect a switch to the the 30 and 87 relay connector? this brings on the fan but not sure if the Amps of work are too much for a little switch. Is connecting to the 85 or 86 points any better or just wire to the thermo switch on the radiator? Any help appreciated. Ta.

I don't have the exact schematics for the vans you all have over there, but if there is a fan relay you can use a light-rated switch to trigger the relay, that is always the best and cheapest way to accomplish this rather than running fat wire and a heavily-loaded switch. You just have to ascertain how the relay is triggered now, is its coil always grounded and power is switched to the other side of the coil, or is it constantly powered and triggered by completing the coil's ground circuit. Could be either way, but VW tends to favor the former. You can find out by probing for power on either 85 or 86 with the ignition switched on. If neither pin is powered, check that one of the two pins is common with ground and the other not. Then bring power via your switch to the ungrounded pin. It is best to get the switching power from the X-bus, so it is load controlled and will shut off during cranking. There is X power on the back of the headlight switch, or at the fresh-air fan switch, wiper switch, and at the fuse panel.

That's the generic way to go about it. In the schematic shown earlier in this thread you would just bring power to pin 86 of the relay for the 200/300w fan shown. But I don't know if those drawings cover all the versions you might see so my description above is how you go about finding out on your own.

[Dantes]

Simon I think you answered your own hypothetical question. Second stage fan on your TDI was insufficient on a flat constantly air feeding motorway; then compare this to a T3 climbing up above 2000 meters from nigh sea-level. That takes some work with a 1600cc motor, when you are hardly moving with its little heart racing you feel for it. When you are going up and down its okay of course, but when you feel like your are at the back of the peloton and constantly climbing mountains to go up its best to act first, before the heat level starts to build to a crescendo. Everybody in montainous Spain fits one, don't know about Africa but here at least I'd recommend it.

Just fitted mine, and you know what even before use its peace of mind. Cheers forum, all the previous articles a good source to get this done. Ta all.

[Simon Baxter]

Simon I think you answered your own hypothetical question. Second stage fan on your TDI was insufficient on a flat constantly air feeding motorway; then compare this to a T3 climbing up above 2000 meters from nigh sea-level. That takes some work with a 1600cc motor, when you are hardly moving with its little heart racing you feel for it. When you are going up and down its okay of course, but when you feel like your are at the back of the peloton and constantly climbing mountains to go up its best to act first, before the heat level starts to build to a crescendo. Everybody in montainous Spain fits one, don't know about Africa but here at least I'd recommend it.

Just fitted mine, and you know what even before use its peace of mind. Cheers forum, all the previous articles a good source to get this done. Ta all.

Used the van with no problems prior to the head gasket going at altitudes up to 2000m regularly.
The head gasket went, it was an old engine, sh!t happens.
No amount of silly switches would have helped.

[Bert2]

Sorry to jump in but does anyone know where to get the high and low temp switches as my low speed is OK but the terminals on the high speed temp switch have corroded off any pointers welcome, ref the switch I think if it makes the driver feel better then go ahead, there are far more mods carried out on these vans that you can argue about that are not required but this old chestnut always stirs up a few remarks. any info on the high switch much appreciated.

[Simon Baxter]

We don't stock them, but maybe we should?
Drop us an e-mail to sales@brickwerks.co.uk and we'll see if we can find some decent ones.

[Bert2]

Cheers Simon
Email sent, If I could get a proper High Temp switch that worked I would get one, but it looks like I will be going down the road of a manual switch unless I can pick a working one up on Ebay as I have been unable to source one to date.

[HarryMann]

Thanks all contributors.. interesting + controversial + informative

Saving and re-posting those wiring schematics for posterity here; then in time whole thread will be copied to Technical Archive forum and the 8090 Wiki Tech linked to that, hopefully creating some etheric permanance.

Radfan_Wiring_032-01.jpg

Radfan_Wiring_TenCentLife_01.jpg

Radfan_Wiring_TenCentLife_02.jpg

PS Interesting about the condition of earths at the crown and the fan..

My Contribution: The TD diesels have the more powerful fans and wiring always looked very heavy to me - shall check the full earth return path though unless someone confirms it is heavy duty back to chassis or battery area

..and whilst it would be hard to overcool the TD diesels overcooling petrols never a good idea, engines are meant to run at the right temperature, not 'just be kept cool' (hence the sophisticated multi-stage fans and very accurate switching temps)

[AngeloEvs]

In the UK the Fan rarely kicks and Fan failure can occur for a variety of reasons due to lack of use. Fitting an overide switch is simple, inexpensive and, if nothing else, offers a convenient means to check that the Fan actually functions as well as being available if the thermo switch fails, unfortunately this component does fail - and when it is needed. I have experienced Rad fans seizeing and bearings suffering due to lack of use. The T25 design is good but not infallible - there are always aspects of it that can be improved as far as I am concerned.

[Red Westie]

Interestingly if you had asked me just 10 days ago about the usefullness or otherwise of a fan overide switch I would have been well and truly in Simons camp 'if the VW system works then why would you ever need an overide'......That was until we took Helga (2.1 MV petrol California) over the 'St Gotthard pass' in Switzerland....Now I can completely relate to situations as tencentlife described earlier on in the thread, where you know the engine is going to get a continuos and sustained hammering in low gears over many killometres, with little airflow through the radiator due to the low speed, where the coolant thermo switch is allowing the engine to rise above the optimal (needle in the centre of the gauge).
I think people have missed the fact that the coolant temperature rises several degrees above optimal running temperature before the fan cuts in and by the time the second stage engages I'm guessing the coolant is at least 8-10 degrees higher than 'optimal' running temp (centre of temp guage)
So a really stressed engine running at the UPPER limits of it's designed engine temperature running range! now the overide starts to makes sense for those EXCEPTIONAL circumstances?

Martin

[HarryMann]

If the switch switches to spec, then the power of the fan is phenomenal (certainly my TD one is) and temps come down quickly, VW have specced this so overheating doesn't happen, by 'their' definition... water going over 100 to 110 isn't overheating, that's why system is pressurised. As long as water (and not vapour) is in contact with the liners and head passages, local overheating is unlikely, impossible even.

TBH, a lot more harm can be done 'long term' by running too cool, than the od excursion to 'hot' on the gauge...

The value of the manual switch I'd say, is as Angelo says, a quick check that all is well, thought of it in that light myself.. in fact my thought was to have a tell-tale LED for the 1st stage fan, as I can't hear that at speed, whereas the 2nd stage is pretty noticeable!

[Red Westie]

HarryMann

VW have specced this so overheating doesn't happen, by 'their' definition...
TBH, a lot more harm can be done 'long term' by running too cool, than the od excursion to 'hot' on the gauge...

Agreed and that's why I was very careful not to use the words 'overheating ' but refering to it as working at the upper limits of the engines temperature range.
Of course it is running within VW's own design parameters but on the upper limit temperature wise and that's what this whole thread has been about.

I also agree with your warning about running too cool long term but knowone suggested leaving the fan permanently on.
I know people can be quite ignorant of the technology and subsequent problems associated with running a cold engine. Most making the assumption cooler is better and some removing the thermostat because they don't properly understand how it functions to regulate engine temperate and enable fast warm up.

Like I said, under normal everyday driving conditions, there should be no reason to modify a correctly functioning thermo switch/fan mechanism but after my own recent experiences I can see that there could be benefits in exceptional circumstances.


Martin

[Simon Baxter]

Good point about a pressurised system, a lot of people don't realise why it is important to have a pressurised system.
Without dicking about with google for hours getting the figures exactly right, but my memory from C&G courses over 15 years ago is that if you pressurise water you raise the boiling point for about 1° per PSI, so a cooling system running at 15PSI wouldn't let the water boil till 115°c.

And again as mentioned, going over the LED isn't "overheating" the needle at the end of the gauge and the water boilling IS over heating.
I would say anything up to 3/4's is normal, some fans don't come on till 3/4's.
I used to do the shopping run once a week from Chamonix down to Sallanches and back again, as noted, low gear up reasonably steep mountain passes, never had any issues, thats on a heavily loaded 1.6TD.

[HarryMann]

It's the oil where there can be more of a temperature issue IMO