Cooing fan not switching off?

[flatyre]

Hey folks started up the tipper today and the cooling fan came on straight away, ran the engine for about fifteen seconds then switched it off, but the cooling fan kept running, had to disconnect the battery to knock it off, it didn't come back on once I re connected the battery. don't think its a thermostat issue, what else could it be?

thanks.

[Stubby]

Stuck relay .

[flatyre]

will see if I can find it and give it the old WD40 treatment. thanks.

[daveatdave]

do not think wd40 will be any good on a relay as they are enclosed and water proof 

[Lazurus]

Was it half way through a DPF regen and never finished - had a similar problem on a diesel Focus as the DPF wasn't getting cleaned up enough - ended up having it bypassed and a remap, all's good now.

[Daniël Bos]

Relays are clever things.

But, breaking a circuit is much more wearing than making one. The contacts get welded together by the current, everytime the relay needs to open or close it makes a spark. When closing the circuit this spark gets smaller as the contacts are moving together, but when opening a circuit there is a current flow to interrupt making not only a bigger spark but the very act of the contacts moving away from each other sort of stretches the spark. if it gets stuck in the closed position the contacts will have welded together by that spark.

 

In short: Just stick a new one in, they cost pennies

[openspaceman]

28 minutes ago, Daniël Bos said:

But, breaking a circuit is much more wearing than making one. The contacts get welded together by the current, everytime the relay needs to open or close it makes a spark. When closing the circuit this spark gets smaller as the contacts are moving together, but when opening a circuit there is a current flow to interrupt making not only a bigger spark but the very act of the contacts moving away from each other sort of stretches the spark

That's why many relays have a snubber diode across the coil, if it doesn't maybe worth fitting one they only cost pennies.

[flatyre]

thanks folks, as soon as I find the relay i'll get a new one!