Force Fans On?

[ukkid35]

How can you force the rad fans on? Does disconnecting the water temp sensor work, or shorting it, or something else I've forgotten?

Thanks

[aide]

I'm sure if you disconnect the water temp sensor the fans come on.
The sensor that feeds the ecu that is.
The one tapped into the steel pipe (that's replaced nowadays by the Act stainless pipes) that's just above the steering rack.

[Boatbuoy]

Correct, pull the plug and the fans should fire up.

[jammy_basturd]

Disconnecting the temp sensor will cause the ECU to take a default value of 97* as the water temp. This should be enough to test the fans but be aware of running for a prolonged period of time like this. Dan @ TaylorTVR advised me that it can cause start issues when cold as the ECU over-fuels.

[Stunned Monkey]

if the engine thinks it's 97 when cold, it will run lean on start-up.

[stlol]

Just remove the relay and get a toggle switch with two leads to bridge the two power connections to power the fan / fans.

[gruffalo]

stlol said:

Just remove the relay and get a toggle switch with two leads to bridge the two power connections to power the fan / fans.

Why when the standard system works fine?

[stlol]

Because the op asked how to force the fans to come on?

[ukkid35]

stlol said:

Because the op asked how to force the fans to come on?

Fans failed recently, just need to find the cause, rectify, and confirm they work without running car to temp.

[ukkid35]

Fuses and Relays seem ok. Other than wiring (which I will check next) what other causes do I need to consider?

[Jhonno]

Have you swapped a good relay in?

I'd be tracing the wiring next.. Unlikely both fans would die together!

[Stunned Monkey]

Mine had a problem with the engine temp sensor causing erratic readout at the ECU. This caused the ECU to chatter the relay powering the fan(s). The PO experienced a dead fan as a result, but the place that replaced it doen't look for the root cause. I found all this out after experienced a dead relay.

I've replaced the engine temp sensor (and both relays) which has made things a lot happier, however I've also wired in an override switch by soldering feeds directly to the back of the ECU PCB. It was the simplest place to get that control without cutting into the loom or removing the ECU's inbuilt control.

[ukkid35]

For anyone who finds this thread it is worth knowing that although the standard ECU Map will force the fans on with just the ignition on, if you have a remap you may need to have the engine running (hot start power saving feature).