Solved: engine fan staying on

[steveiy]

I thought I'd share my experience for the benefit of whoever it was that had the same problem a couple of years ago. Bleedin' annoying, but quick to cure once you know.

Car: 1998 Chimaera 450

Problem: Engine fans were coming on when the ignition was switched from on to off, even if the engine wasn't running. Only happened infrequently, but when they did come on they stayed on. The only way out was to start the engine and run for 10 minutes until the thermostat cut in, resetting the relay.

Solution: find the engine fan relay (a little yellow one on my car) and swap it with one of the other ones of the same type. I chose the headlamp dip relay. Now the problem's gone away. Yippee!

And no, before you ask, I don't get the headlights staying on...

[Tim-b-123]

Thanks Steveij - I found the relay and changed it (success !), reporting back on my initial thread.
Thanks for the help.

[jonathant]

here too success[1]! Thanks muchly after 18 months of head-scratching.

[1] well, I think so, the symptom of seeing and hearing the fans just-but-not-quite kicking in when ignition off has now gone...

[MrE]

Can anyone point a dunce (me) in the right direction of this relay?? Thanks.

[Bunglist]

MrE said:

Can anyone point a dunce (me) in the right direction of this relay?? Thanks.

You will have to scrabble around in the passenger footwell, but on mine the relay was the top Left on the fuse board basically the one that is the most awkward to get to.

[MrE]

Managed to identify them in the end - thanks for the post regardless. Swapping them around however, has not solved the problem. Now thinking maybe the problem lies with the thermostat??

[BryanWilton]

A Thermostat is just a switch, if you take the wires off the thermostat & the fans stop then the thermostat has probly gone 'closed circuit' & the Thermostat is probably faulty
If the fans don't stop its not the thermostat
When you say thermostat i assume you mean the Fan switch (Otter switch)?

I believe most cars(if not all) have separate Thermostat as part of the cooling system which is nothing to do with the Fan switch, i think the thermostat controls the water pump, could be wrong on that though?

[Littletidnock]

And no, before you ask, I don't get the headlights staying on...

[/quote]

Might be worth changing the now head lamp relay, you may inadvertently flash someone out of a junction into your path, that may stop the fans working altogether

[Littletidnock]

MrE said:

Managed to identify them in the end - thanks for the post regardless. Swapping them around however, has not solved the problem. Now thinking maybe the problem lies with the thermostat??

if you pull the wires of the otter switch do the fans stop

[Cider Andy]

BryanWilton said:

I believe most cars(if not all) have separate Thermostat as part of the cooling system which is nothing to do with the Fan switch, i think the thermostat controls the water pump, could be wrong on that though?

Yes, they all have a traditional mechanical thermostat that controls the flow of hot coolant from the engine into the radiator, via the swirl pot. It doesn't control the water pump though, the water pump is mechanical and runs all the time. All cars (unless modified!) have an 'otter' switch to control the fans. Earlier cars have this mounted in the swirl pot, later cars have it mounted in the radiator.

[BryanWilton]

Thanks Cider Andy
I was close, but no cigar

[Littletidnock]

Cider Andy said:

BryanWilton said:

I believe most cars(if not all) have separate Thermostat as part of the cooling system which is nothing to do with the Fan switch, i think the thermostat controls the water pump, could be wrong on that though?

Yes, they all have a traditional mechanical thermostat that controls the flow of hot coolant from the engine into the radiator, via the swirl pot. It doesn't control the water pump though, the water pump is mechanical and runs all the time. All cars (unless modified!) have an 'otter' switch to control the fans. Earlier cars have this mounted in the swirl pot, later cars have it mounted in the radiator.

the thermostat does work in conjunction with the water pump albeit it does not directly control it. When closed the thermostat does not allow full circulation of the coolant via the water pump a small amount flows through the bypass hose, when open full circulation through the radiator is allowed.

[MrE]

Littletidnock said:

MrE said:

Managed to identify them in the end - thanks for the post regardless. Swapping them around however, has not solved the problem. Now thinking maybe the problem lies with the thermostat??

if you pull the wires of the otter switch do the fans stop

Yes, if I disconnect either of the wires on the otter switch (mounted on the radiator), neither fan works. Does that mean that fault lies here or not? Would it be worth buying brand new relays?

[BryanWilton]

I would say that indicates the otter switch is fauty
Have you got a multimeter?

If you have then check the continuity across the terminals with the wires disconnected(when its cold)
If you get continuity across it when its cold, its faulty

[MrE]

Unfortunately I don't.

Is it a cheap and easy job to replace the switch? I'm happy to have a punt on that being the cause if can do it myself without too much bother. Where can replacements be found?

Thanks for your help btw

[BryanWilton]

The TVR Shop (online website)
£15 Odd, plus VAT & postage, i'd go for the early switch on type as recommended in 'The Bible'

I think i remember someone on hear saying that a landrover one fits but they tend to go wrong so use a TVR one...
I might have imagined that though (:

[BryanWilton]

Please excuse my awful spelling!

[BryanWilton]

Do a search for 'fan switch' on that website not otter switch...

[MrE]

Thanks, I'll let you know how i get on.

[BryanWilton]

Ok, good luck with it