Thermo Fan won't turn off

Hi,

All the threads I have looked at talk about the thermo (electric) fan not coming on. My problem is that it won't switch off.

Happened once before and I walked away expecting it to shut off once it had cooled down enough, I had been having overheating problems but since solved by replacing the blocked radiator. At that time I came back to find the battery flat.

Didn't happen again until......

A few weeks later now and I switched off after arriving home and the fan kept running (something I don't recall normally happening even after 14 years of ownership).

Went back out a while later and still running, so I disconnected it. The next morning before starting up I reconnected it again and it still wanted to run.

I suspect something to do with a controller or thermo switch but would like to know before I start replacing parts based on a guess.

Thanks,

Guzzi

Post year/engine for most accurate results.

Normally, the e-fan is controlled by a relay, most likely inside of the power distribution box under the hood if its a 4.0

I'd try swapping that relay with another one (they are all the same part number so it's okay) to see if that resolves your problem. If it does, you know what relay to replace.

If that isn't it, suspect a problem with the coolant temperature sending unit that controls the fan.

Hi,

Sorry about the info. oversight!

1996 XJ 4.0 6cyl with 230,000kms

Engine mods include

Hi flow water pump and thermostat housing, ADRAD Radiator.

Thanks for the reply, I will do the swap around this evening and will post findings.

Guzzi

it would almost have to be the relay, as the fan control circuit is only powered when the key is on. A stuck relay, however, has the ability to complete the circuit to the fan even without the key.

The same thing happened to mine last year. Bad relay = Dead battery.
Same type of relay that controls ac clutch and that one died on me a year earlier. Another dead battery.
I keep a few extras in the glove box now. Just in case.

Hi,

Thanks to all for the great feedback suggestions.

Took a punt and invested the princely sum of $12 in a new relay and it seems to have cured the problem.

The old relay could be made to work by taking the cover off and un-sticking it but I believe that once it got hot from use/engine bay temp. it would fail to earth and therefore leave the fan running.

Thanks again, saved me the min service charge at the Auto. Elect. and down time on the vehicle.

Cheers,

Guzzi

Relays are good salvage yard items, get a couple of handfuls for $5.