[Mk2] [Generic] engine lid fan

[jack-p]

I got given a fan to put into the engine lide so I thought why not.

it has two wires and I'd like to wire it in so that it comes on with the engine fan.
is it these wire I need to splice into or will this not work?



Thanks

[Peter Gidden]

Use the existing fan wires to switch on a relay. Feed your new fan through the relay. Job done.

[jack-p]

If I put in a relay what exactly will that do? I'm not exactly up to speed with electricals

[craig]

If I put in a relay what exactly will that do? I'm not exactly up to speed with electricals

existing fan wires energise a relay. Relay contact makes, and this controls your new fan

[jack-p]

I see, so it's a way of splitting the energy?

Without wanting to come accross as lazy where would I get one/what type of relay am I looking for? An ebay search seemed to bring up alot of different types most of which were flasher unit relays.

I take it the wires on top of the engine fan in the pic I put up are the correct ones to use then?

[Peter Gidden]

A relay is a device that uses a small current flow to switch a large current flow.

Google "Bosch relay" and you'll find loads of info. Halfords, Maplin and all car spares shops will have what you want. About £4.

You need a 4 pin Bosch-type relay.

[jack-p]

Okay cool, I'll try to get it done tomorrow afternoon and let you know how I get on.
Cheers guys

[slipping clutch]

I did this a few years back- cannot take credit for it though as its an ats racing mod ( or thats where I first saw it and bought the fan from) - its really quite effective given that a large part of the fan is covered by the rain tray But as peter has already stated use a relay - I did at first just pull into the cables youve shown and sparked it up to see if it worked - instant problems !!! the fan just draws too much current. Also at first I had it switching on and off on the temp. sensor in the engine bay but changed it over to a switch in the cabin.
Hope this helps.

[jack-p]

Oh cool, that's good to know. To be honest overheating isn't an issue since my cars just an n/a but it wont harm keeping it cool.

I'm hoping wiring it in this way will activate it by temperature, my theory being it will just kick in when the other fan does. Is that right? and why did you change it to a switch?

My main concern is the noise but guess I'll just have to see how it goes.

[shinny]

Just out of curiosity, do you know what size fan you need to fit in there?

I'm tempted to punt on these: http://www.ebay.co.uk/itm/350568218465

[jack-p]

Mines a 12" fan I believe and fits in there perfectly. It's held in position quite tightly by the rain tray so does't need securing whereas a smaller fan may do.

[KarlBristol]

It is a 12"

This one isn't produced anymore, but I spoke to the original seller and this is pretty much identical just a bit cheaper (they get the parts from a different supplier now )

http://www.ebay.co.uk/itm/Electric-Radi ... _937wt_689

Looks really good in there mate
Pleased that one of us got around to doing it, lol

[slipping clutch]

Hi Jack, I swopped over to a switch in the cabin when I fitted my spearco i/c - it made no sense to me to wait until the spearco got heatsoaked beforee the fan kicked in so I wired up the boot lid fan and the i/c to come on when I wanted too. I also swopped to an aftermarket engine lid which alowed me to run 2 fans - the second fan is wired to the temp switch now.

[KarlBristol]

Wired in today jack?

[jack-p]

nope, haven't had time yet. I went and got the parts so will hopefully crack on with it tomorrow. I got a relay with a fuse because it was a couple of quid cheaper, guessing there's no real difference?

[jack-p]

Okay well I'm a little confused with how to wire this up so if anyone can spell it out for me that would be great.

I have two wires on the engine lid fan (the one im trying to wire in) and two wires going to the engine bay fan (where I plan on taking power from).
The relay has four pins:
30 - battery/power
87 - accessory (in this case the engine lid fan)
86 - switch - supply from ignition or lighting
85 - earth

My question is, what gets wired into where.

I know this is basic for most but the is my first attempt at anything like this so it's got me a little confused.

[shinny]

Wire 85 and 86 to the two going to engine bay fan (doesn't matter which side is which)

Wire 30 or 87 to another 12V source (preferably fused... the screws under the rubber boot in the rear fuse box will work if you must, tho it's not ignition switched or fused so will always be live unless you disconnect the battery)

Wire the other pin (30 or 87) to one lead from the fan

Wire the other lead from the fan to ground

Your fans should now go on and off together. If your new fan pushes instead of pulls, reverse the wires going into it

[jack-p]

Exactly what I was after, great answer and thank you.
Is there anything else nearby that would work better than the screws under the rubber boot as I'd really rather it wasn't constantly live?

[shinny]

Well, if you think about it, you're just creating a new switched live by adding your relay... just it's switched on the engine bay fan rather than the ignition (which itself is ignition switched). Put an inline fuse on there and I really don't see a problem

Now, you could get more clever and pull the power from the engine bay fan instead... the VENT fuse is 20A so more than capable of running both the fans. The blue wire with the black stripe is the positive side of the engine bay fan, so you could use that instead if you wanted...

At this point, I'm not sure how useful your relay is. I know you can't just wire the fans in parallel, as the fan control unit in the boot will shut them down for taking up too much current. What I don't know is whether you can connect the fan from the blue/black wire to ground and it work as expected, or whether you still need to relay to get the two to match up. (The reason being, I'm not sure if it's the relay in the fuse box or something in the control box that controls the stock fan to turn on.

[shinny]

Hi Jack, I swopped over to a switch in the cabin when I fitted my spearco i/c - it made no sense to me to wait until the spearco got heatsoaked beforee the fan kicked in so I wired up the boot lid fan and the i/c to come on when I wanted too. I also swopped to an aftermarket engine lid which alowed me to run 2 fans - the second fan is wired to the temp switch now.

Just a note on this, the previous owner of my car had rogue fans fitted (which I removed as I was getting annoyed at water ingress) and was controlling them directly from a switch by the fog light switches. However, that switch got extremely hot running 13-14A through it and would burn your knee if it got dislodged!

There's nothing wrong with switching fans in the cabin, but be careful of the currents involved and use a relay where required (or a properly rated switch if you must)