Scirocco Register

Morning all,
Looking for a bit of help with my MK2 Scala, and overheating issues due to the radiator fan no longer coming on.

The last few times I've run the car she's overheated, and the fan shows no sign of coming on even when the temp gauge is up to the right edge of the scale.

So far I've done the following:
- replaced fuse
- replaced old knackered radiator
- replaced rad temp switch (2 pin)
- replaced water pump and thermostat
- squeezed top hoses with engine running to try and get ride of any air pockets
- hooked fan directly to battery with jump leads to check motor works fine, which it does
- hot air coming from heater ok
- all hoses getting warm, including bottom hose from thermostat



No idea what else to try to be honest. The only other thing that comes to mind is that the wiring to or from the rad temp switch is no longer working perhaps?
Any help would be hugely appreciated.

what colour is your radiator cap?

the black ones can cause this.

DannyH wrote: ↑Thu Sep 09, 2021 3:44 pm what colour is your radiator cap?

the black ones can cause this.

The colour change is widely rumoured to indicate a technical improvement, but this is apparently a myth - I have seen on a German VW forum an extract from an email from VW confirming there is no technical difference. Black was the colour in use right up to the end of Scirocco production. The switch to blue came later, I suspect just part of a migration to the colour codes for caps VW use today - blue for water, black for oil, yellow for brake fluid, etc.

That said, I am sure these can fail, perhaps not holding pressure, which would lower the boiling point of the coolant, but I'm not sure that would explain the fan not coming on when the instrument temp gauge is at max. That sounds more like an electrical fault to me.

GT_II wrote: ↑Thu Sep 09, 2021 9:41 pmI have seen on a German VW forum an extract from an email from VW confirming there is no technical difference.

Having located said email again, I realise this related to the later wide flat coolant cap fitted to the Golf Mk2 and other VWs, which underwent the same colour change during the 1990s, prompting various rumours circulating online that the colour change signified a reduction in pressure, most commonly cited as from 1.5 to 1.3 bar, an improvement in design, or even a more heat resistant plastic. These rumour were apparently fuelled by a spate of heater radiator failures, as well as variation in quoted pressure specs for some after-market caps. VW's email confirmed there was no difference in spec between the two different colour caps.

My bad, wasn't paying attention of course it won't affect the fan!

However I and others had huge problems with dodgy (usually black) radiator caps

PS VW doesn't have a very honest reputation when they give specs!

It's a fairly simple system - the rad fan earth wire is a permanent earth. Permanent 12v+ power is supplied to one terminal of the rad fan switch. At a certain temp it allows that current through to the fan.

Take the plug off the fan switch and bridge the two terminals - if the fan comes on you know the wiring is OK.

After that there are limited possibilities:

• Even though you have a new switch it might still be faulty - easiest enough to test with some hot water. Also make sure you have the right one, ie correct temp rating.
  
  If the switch is OK, is the radiator around the switch area getting hot? Are both top and bottom rad hoses getting hot. If not, there may be an airlock. When you refilled the system after all the works did you run it for a few mins with the expansion cap off?
  
  Lastly, is it actually overheating? The gauge could be faulty. A cheap IR gun from Amazon/eBay is a worthwhile investment and will tell you actual temps of the hoses

mr.brown wrote: ↑Sat Sep 11, 2021 10:29 am Take the plug off the fan switch and bridge the two terminals - if the fan comes on you know the wiring is OK.

If the fan doesn't come on with this test, check whether you have 12V between the terminal with the red wire and an earthing point. If you don't, check for 12V at the two-terminal connector which feeds the radiator fan circuit, which I think is located fairly close to the left chassis leg near the radiator. If you don't have 12V here, there may be a fault in the wiring from the fuse board to the 2-terminal connector.

If you do have 12V at the fan switch, Check continuity of the wiring between the fan switch and the fan, then test continuity of the wiring between the fan and earth, via the two-terminal connector.

Thanks all, I'll look into the wiring next by the sound of it.

Out of interest, I've noticed on the loom before the rad switch / fan connection there is this rather odd looking connection. Is this supposed to be there, or is this a sign of a previous wiring repair? If it's been repaired I'll definitely be opening this up to have a look at the condition inside too.