[Mk2] [Turbo] Wiring engine lid fan.

[kirk]

Hi guys, I realise this has probably been covered a lot previously but I can't seem to find a proper answer.

Basically I want to run an engine lid fan to help cool the engine bay a bit better during the warmer months. My question is how can I wire it in to come on when my IC fan comes on? Is there a way to do it without the fan controller shutting it off due to too much load on the system?

I don't know if this is a problem or not but I wanted to check. Any info would be great. Please don't be mean

[alanmr2turbo]

Why not just run the fans full time?
Isn't that the best way of sucking out engine bay heat?

[juliankv73]

Why not just run the fans full time?
Isn't that the best way of sucking out engine bay heat?

You could also wire it with a switch

[Pauln]

Or run the new engine lid fan(s) via a separate power supply is switched on and off by a relay with the relay coil connected to the IC fan circuit. That way the additional load on the IC fan circuit should be minimal.

Paul

[Bear87]

I agree with Paul (and he really knows his stuff) putting a relay in is the best way to ensure your not overloading the circuit. The fans draw a reasonably high current so a dedicated power supply of sufficient thickness of wire will increase reliability and lower risk of fire etc. Also don't forget the fuse the circuit!

[kirk]

Or run the new engine lid fan(s) via a separate power supply is switched on and off by a relay with the relay coil connected to the IC fan circuit. That way the additional load on the IC fan circuit should be minimal.

Paul

As I'm pretty average at wiring how would I go about doing that?

[Pauln]

First you need to check what current your new engine lid fan(s) are going to draw. Look for a label on the fans or ask the seller, but as an example a single 240mm fan could draw as much as 8amps.

Once you know the current draw you can purchase an inline fuse holder, relay and cable from the likes of Halfords or Maplins of suitable for that current.

Here's a rough sketch of how to wire your new fan(s) up.



Automotive relays usually come with the terminals numbered 85 and 86 for the relay coil and 30 and 87 for the supply you want the relay to switch.

You should then pickup a new supply and feed this via a suitable fuse to terminal 30 on the relay.

Then tap into the existing two wires that connect to the IC fan and run additional cables to terminals 85 and 86 on the relay.

When the IC fan comes on it will then power the relay coil which will in turn switch on the independent supply to your new engine lid fan(s).

Hope that all makes sense.

Paul

[kirk]

The fan I intend on running is has a 7 amp draw.

Would the 12v supply from the fuse box be suitable? Granted it would be live all the time rather than a switched 12v but it's probably the closest thing without tapping into other wires.

I'm guessing I just need a bosch type 4 pin relay as well?

[Pauln]

Bosch type 4 pin relay should be fine, just make sure it's rated t at least 10 amps as the starting current on a motor is often a bit higher than the running current.

It's a fairly substantial looking feed to the engine compartment fuse box, but I don't know if that's straight feed from the battery. It should be OK, but if it's a fused supply, I've no idea how much spare capacity there is.

As no current will be drawn by your new fan unless the IC fan is running it shouldn't really be an issue using a non ignition switched supply.

Paul

[kirk]

Thanks a lot Paul