Mk3 Cavalier Owners Club | Vauxhall Cavalier Dot Com

I'm going away with my caravan next weekend and when I used the cav to move the van home the other day it got abit hotter than I'd like

Vauxhall in my experience always set the fans to turn on just as the engine is about to explode which somehow seems to be ok in normal driving but as I'll by dragging a caravan behind me keeping the engine at boiling point for a long time doesn't sound too clever to me

So does anyone know how to 'override' the fans so I can turn them on with a switch on the dash? For reference it's a 93 td hatchback with front and back rad fans. They both work but as I say only when the temp gets close to 90 and with the van on the back it was creeping over the 90 mark.

I'm hoping there's a relay I can just tap into, and if so, can I just wire up a 12v feed to turn it on or will that cause issues? I'd assume because there's no ecu it should be ok to just tap straight into it???

This has been covered before somewhere as I wanted to do the same thing when my V6 fan was playing up... There is no ECU as such for the fan, it just runs off the temperature switch, if it's not a hot day, then you can whack the heater on full blast to dump some excess heat out of the system, it will help slightly, failing that you can wire in a switch if you like, I don't know exactly how though, someone can help who knows more in detail about it.

Whenever I have had fan switch problems, or a burst radiator,
I have shorted the switch out on the radiator using a 20 amp blade fuse with the blades twisted to fit snugly.

Always got me home without killing the engine.

You could splice in a relay to short out the rad fan thermo-switch pins. In a similar way that I did with a blade fuse.
Then use a dash mounted switch to operate the relay.

I can do a quick wiring diagram later if you need further explanation.

Okay pictures coming up...

On the standard 2 pin thermo-switch, there are two thin wires.
Haynes quotes 0.75mm csa.

On the three pin switch, the wires are much beefier
Brown and Brown-Yellow are 4mm csa
Brown-White is 2.5mm csa

For the link bit between the connector and the fan switch, I would suggest that you use the same size wires as the original wires to the connector.

You could splice directly into the loom wires - but please use soldered and crimped joints and heat shrink sleeving.
NOT THOSE CRAPPY SCOTCH LOCK THINGS.

So for 2 pin , 20 amp relay would be fine.
For 3 pin, I reckon you should go up to a 40 amp relay.

So less waffle - here are the pictures.

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From what I have heard you can use the aircon switch to wire in an override (on a car with the aircon removed), but I have never found a wiring diagram.

If you have ac you can just turn it on and you'll get a low speed fan constantly. It runs the fan to keep air flow through the condenser.

My car used to have air con, but it has all been removed for intercooler, etc... I believe you can use the old wires / switch to wire in an override for the fan?

if as you say the fan comes on at 90, you have nothing to worry about, thats about normal running temp, the fan on my cav turbo comes on about 95 - 96 normally, i wouldnt worry until the temp gets up to 100 or so. Ads

For mine anything over 75 is hot, I thick its a izusu thing because my frontera 2.8 also runs colder than 'normal' at around the 75 mark too.

Cheers for those diagrams, from memory the switch in the rad has 3 wires so I'll have to investigate that. I was hoping there would be a relay for each speed that I could just tap into avoiding having to add any thick gauge wiring but oh well lol, such as life

Oh and I don't have a/c

I'll keep you all posted when I get around to doing it later in the week

The three pin diagram was based on the wires to the Turbo Diesel Engine in the Haynes manual.

There are two relays in the Diesel Cav, but I could not say where they are.
those big chunky wires appear to come from the relays, all the way to the two stage thermo switch and then to ground.

Oh, and diesels do tend to run cooler anyway. - My Vectra-C 1.9CDTI kicks in at about 85 degrees.

Back to your car -
You'll probably find that the first fan cuts in at around the mid-seventies as you describe, and then the second stage will kick in at around the mid-nineties degrees celcius.

The temperature that the fans appear to kick in at is all subjective, as it depends upon the accuracey of the thermostat mounted temperature sensor and your temperature gauge.

My father in law used to have an early Corsa-C that got upto an indicated 103 degrees before the fan kicked in. It never over heated though.

The relays on the td are in the under bonnet fuse box, two green ones I think they were Thought about doing this to mine because long hill climbs can see it reach over 100 on hot summers days. It never overheats though and when I thought about it they'd be on full blast anyway via the rad switch lol. Mine runs just over the 90 mark normal daily driving and I think the fan cuts in about 96/97. They get hot quick fast road, heavy load driving.

Great diagrams Robsey, handy for future reference.

When I did mine I was in a hurry so just cut the original wires for the relays coils and wired them up on a switch only. Risky in that the car now can't turn the fans on itself but as it turns out the fans don't need to be on if the cars moving at a constant speed without a trailer on the back. The fans only need to be turned on if stood still for more than a few minutes.

I've got 2 switches, one for low speed and one for hi speed, the high speed won't turn on unless the low speed is turned on. By the looks of it the front fan is a slave fan to the larger back fan so that when in the low speed mode both fans are connected in series thus getting about 6v each then turn it to high speed mode and it grounds out the back fan effectively cutting out the front fan so the back fan gets the full 12v thus spinning much faster

I hope that makes sense lol. I'm the only person that drives it so I'm not that bothered that the car can't turn the fans on. But it towed my caravan last week without any problems with the fans on low constantly and flicking upto high for the long motorway hills. Only got near the 90 mark twice I think so well chuffed with that

Hi guys, can anyone recommend somewhere to get hold of a radiator fan switch ( good quality ) for a cavalier turbo C20Let & part number, thanks claire

Hi Claire,

The part number you want is -
90339500

The price for a genuine GM part is £22.60 plus postage from Genuine Parts Search.

Just to confirm yours does NOT have the permantly attached short length of loom between the connector and the switch body.
In other words, the connector plugs straight into the switch body.