fan relay switch

[wkulestat]

I was wondering if anyone has ran a fan relay to a switch inside the car so that you could turn the fan whenever you wanted to, but it would still come on if it got hot enough, if you didn't turn it on. If someone could help me out, I would appreciate it.

 

[Doug99RS]

The obvious question to me is WHY???

But to answer your question... there have been others that have wanted to do this but have not had any success. The reason being here that the computer checks the circuits for the relay and if there's a problem, it will throw a code.

Here's some reasons why you should NOT mess with this system.

The computer is set up to turn on the radiator fan when the engine coolant temperature reaches a certain temp. Anything above that temp will cause the engine to get to hot and start damaging the engine or causing performance problems. The circuit is rather simple for this relay. Basically when the temp gets high enough a very small voltage is sent to the relay. This voltage trips the relay which then completes a second circuit inside the relay itself. This second circuit carries alot more voltage through it for the fan itself. By doing this the computer only has to deal with a small amount of voltage and has other components deal with the larger voltage. This cuts down on the temps inside the computer.

What you're suggesting would involve breaking up one of those two power circuits with a user controlled switch. There's no fail-safe way you can do this because there's not multiple levels of voltage being sent to the fan relay based on temp levels. Either it's on because it's too hot or it's off because it's cool enough. You'd be interupting the ONLY signal wire for the circuit.

So back to the original question of Why? And then maybe other suggestions could be made to do what you're trying to do.
Doug

 

[wkulestat]

the reason why i want to do it is because when i go to the drag strip, i like to keep my engine as cool as i can, and with a fan relay i can keep it on and cool off my engine quicker.

 

[Doug99RS]

the reason why i want to do it is because when i go to the drag strip, i like to keep my engine as cool as i can, and with a fan relay i can keep it on and cool off my engine quicker.

That's a reasonable response. Pull out the relay for the fan, jump pins 30 and 87 of the relay itself together with a piece of wire. This will complete the circuit. This won't set a code because you're still not messing with the control circuit which is controlled by the PCM.
Doug

 

[wkulestat]

oh, and i am not taking about cutting into the wire and separating it,.. i am talking about splicing into it, and using a separate relay for the switch

 

[Doug99RS]

oh, and i am not taking about cutting into the wire and separating it,.. i am talking about splicing into it, and using a separate relay for the switch

Refer to the previous post for a way to do it. Judging by what you want to do... you can achieve this without having to hack any wires. Further down the road you will thank yourself for not hacking up your wiring harness. The jumper wire is non-intrusive and wno't damage anything.
D