radiator fan won't turn off

[dansk]

hi ... so the other day, stopped our camper and the radiator fan kicks in. Athis has a tendency to drain our battery so its become common for us to remove the fuse for the radiator fan except rthis time nothing happened - as in the fan still powered away at full strength depsite the engine being cold, the outside temp below 10 deg and the fact that I had removed the bloody fuse! How can the fan still work with the fuse disconnected? What do I need to fix?

[CovKid]

Been a while since I messed with the fan circuit but given that there are two speeds and therefore two circuits, plus it will run for a certain amount of time with engine off when radiator is hot (or when it THINKS it is hot), it could be the the radiator thermo-switch has failed and causing it to stay on indefinately. I'd change that first (they don't last long from experience). The fuse you removed may only affect the one circuit. I just don't have the circuit diagram in front of me but I'll bet the thermo-switch on rad is the culprit. When working correctly, once the switch detects temperature has dropped, it should go open circuit (ie fan go off) but sounds to me like its stuck.

Cheap to replace and a quick job really.

[kevtherev]

My thoughts too.
The fan switch can be removed and replaced without draining coolant
And if you're quick, without the need to bleed.

[CovKid]

Aye, and post a pic of old thermo-switch. I've swapped out some very deformed ones over the years. They're always interesting to look at

[kevtherev]

You're weird.

[Oldiebut goodie]

He is wired also!

[itchyfeet]

Agreed switch,

mine started doing the high speed only recently, cutting in and out randomly, swap switch is a 5 minuite job do it quick and loose virtually no coolant, no bleeding required.

[CovKid]

My last one

[kevtherev]

Nice picture.
Is that the one on your bedside table?

[CovKid]

Nah, don't be silly. I keep old brake pads next to the bed

Seriously though, that last one was all dished in the centre - well weird.

[itchyfeet]

typical fan circuit in haynes shows seperate fuse for 2nd stage but in a VW diagram shown as same fuse for both stages.

if you are not pulling the wrong fuse it most likely it has second fuse somewhere, the only other explanations I can think of is shorts between wires due to overheating or somebody has modified wiring before.

[CovKid]

You'd think it would be two fuses - for redundancy otherwise at a standstill with engine running (ie in traffic) there'd be no cooling at all if one fuse popped. VW tended to make changes as they went along though and didn't always get things right - like shoving wipers and dash blower on one fuse for instance.

Fuses and shorts aside, if the rad fan isn't running when you start off, but comes on and stays on forever when you park up, then its thermo-switch. Remember, its designed to keep running for a minute or so when coolant is excessively hot, so if, after replacing switch, its still running even for a short time after you've stopped in what is now relatively mild weather, you may also have an overheating problem because normally the fan delay after you switch off tends to be a Summer or heavy traffic thing. When you pick up speed, the air ram effect is more than enough to keep water cool unless its in the 90s out there. However, if it does go off after a minute, then at least you know its doing its job.

All roads do point to thermo-switch. Have the new one in your hand ready and when you remove old one, you'll lose very little water at all. Best done when rad is cool obviously. As the switch ages, it will tend to get inaccurate anyway. Better stuck on than stuck off.

[kevtherev]

. Remember, its designed to keep running for a minute or so when coolant is excessively hot,:

I wonder if this is being misinterpreted?