Flamin' fan!

[rovamota]

The (noisy) fan keeps cutting in on every journey on my BRM, and at the Beaulieu meet Adam suggested replacing the fan transducer. I bought one from my local dealer and fitted it, but the fan still comes on no after a few miles no matter. Temperature is normal, everything else is okay.

I was having trouble with a fast idle problem on it and everything possible was replaced, then one day I knocked the ECU whilst the engine was running and the revs dropped back to normal! I have to do this quite regularly to get the engine to idle respectably. I can only conclude that there's an internal fault with the ECU.

Any suggestions?

Kev.

[Dom]

buy a bigger hammer?

Are keys/instrument consoles coded to the ECU? I'd imagine that would make replacing one a complete pain in the arse :(

Bite the bullet, go for a megasquirt and tune the bugger ;)

[soberphil]

Hi Mate,

I have the exact same problem - fan coming on really early yet car not overheating.

Had it in the workshop and fan seemed to be coming in when top hose was getting to about 90 degrees and cuting out when it got back to about 85 degrees.

I think the actual figure it should come in is 104 degrees (I'll check that). I suspect the coolant temperature sensor is playing up, so I have bought a new one, but as yet I haven't fitted it.

A few people told me that if the fan is coming in early not to worry, but I think that overcooling isn't a good thing, plus the coolant temperature doesn't just affect the fan, the ecu uses it to adjust other things like ignition timing, so the car can't be running at its optimum.

I'll hopefully get round to fitting the new temperature sensor, new coolant and new rad next weekend. I'll let you know if it makes any difference!

What is the fan transducer that you speak of?

Cheers,
Phil.

[soberphil]

Just checked the temperature the fan should operate:

Cooling fan operation:
Heater cars:
On - 104°C, Off - 98°C

Air conditioned cars:
Slow speed On - 104°C, Off - 98°C
Fast speed On - 112°C, Off - 106°C

[rovamota]

Hi Mate,

What is the fan transducer that you speak of?

Cheers,
Phil.
The fan transducer sits below the CTS on the cylinder head outlet. You have to be quick when swapping them over to save having to refill the cooling system and bleed it! Costs about £14.

Kev.

[rovamota]

Right, it would seem after a lengthy period of trial and error the cause of the fan staying on was the earth connections on the slam panel just in front of the battery. Here you'll find 3 wires, one direct from the battery, that all meet up and are held in place by an 8mm bolt. I've undone it and cleaned up the connectors and the bolt hole with abrasive paper and now the fan seems to operate correctly, switching on and off intermitantly instead of coming on and defaulting to fast speed and staying on until the engine is switched off.

The moral I guess is if you are having cooling fan issues then check all the earth connections before going down the route of replacing sensors and the like and still having the same problem.

Kev.

[Adam]

Glad you found the cause at last. Amazing how such little things can cause such problems.

[soberphil]

Right, it would seem after a lengthy period of trial and error the cause of the fan staying on was the earth connections on the slam panel just in front of the battery. Here you'll find 3 wires, one direct from the battery, that all meet up and are held in place by an 8mm bolt. I've undone it and cleaned up the connectors and the bolt hole with abrasive paper and now the fan seems to operate correctly, switching on and off intermitantly instead of coming on and defaulting to fast speed and staying on until the engine is switched off.

The moral I guess is if you are having cooling fan issues then check all the earth connections before going down the route of replacing sensors and the like and still having the same problem.

Kev.

This is of great interest to me - having replaced sensor, rad and thermostat I thought I had this licked, 'till the thermostat housing started to leak, so I replaced the housing (and stat again), and all was well for a while but the problem has since recurred. I shall investigate asap (which may not be for a while), so thanks for the advice!

[soberphil]

Right, it would seem after a lengthy period of trial and error the cause of the fan staying on was the earth connections on the slam panel just in front of the battery. Here you'll find 3 wires, one direct from the battery, that all meet up and are held in place by an 8mm bolt. I've undone it and cleaned up the connectors and the bolt hole with abrasive paper and now the fan seems to operate correctly, switching on and off intermitantly instead of coming on and defaulting to fast speed and staying on until the engine is switched off.

The moral I guess is if you are having cooling fan issues then check all the earth connections before going down the route of replacing sensors and the like and still having the same problem.

Kev.

Did you do anything else around the same time? I've now cleaned up the connections and my problem persits! It's getting me down! Strange how it seemed better for a while after I changed the thermostat - could another (a third) have failed?! I feel not - as I'm getting flow through the system and no overheating.

[rovamota]

Well, I thought I'd cured it. but I haven't. Fans come on even in this cold weather, but I did find this info;

"Problems with cooling fans sticking on: This fault is a rarer but known problem. The 2 black Vi solenoids that control the valve timing can cause "voltage spiking" problems via the MFU and keep the fans running. The engine ECU interprets the engine coolant temperature as 60celcius, and as a back up mode brings the cooling fans on all the time. in really bad cases, if the cooling fans are stuck on from cold, starting problems may occur, as there will be no fast idle."

If I knew what I was looking at maybe I could sort it.

Kev.

[burrows]

I know this isn't much help but I had similar problem with the fan coming on a couple of years ago, it continued for months so I mentioned it when the car went for a service, I don't know what they did but I've had no trouble since and there wasn't an extra charge on the bill so assumed it was a minor job.

[soberphil]

Well, I thought I'd cured it. but I haven't. Fans come on even in this cold weather, but I did find this info;

"Problems with cooling fans sticking on: This fault is a rarer but known problem. The 2 black Vi solenoids that control the valve timing can cause "voltage spiking" problems via the MFU and keep the fans running. The engine ECU interprets the engine coolant temperature as 60celcius, and as a back up mode brings the cooling fans on all the time. in really bad cases, if the cooling fans are stuck on from cold, starting problems may occur, as there will be no fast idle."

If I knew what I was looking at maybe I could sort it.

Kev.

Yep - it's a really strange one this, but I'm determined to get to the bottom of it eventually.

I've never had the fan come on immediately from start up but often very soon after. The poor starting would make sense - if the ecu sees 60celcius it won't provide enough fuel for a cold start? Come to mention it mine has started like a dog a couple of times this week. It always fires but runs very roughly for a few seconds before the idle sorts itself out.

Anyway, the question is, where to go from here...

My next check was going to be the relay for the fan - maybe voltage leak is causing it to switch when it doesn't need to!? After that I'm not sure where to go- if it is voltage spiking from the vi solenoids (or anywhere else) then I guess some sort of suppressor would be required - perhaps it has failed.

I tell you what is strange - that after I changed the thermostat and after you'd done some work we both thought we had it fixed for a while - conclusion: maybe it is something as daft as a loose or worn connection somewhere and we'd both disturbed it during our efforts such that it worked for a while?!?!

I'll continue to post any findings here.

p.s. another piece of information for the jigsaw (don't know if it is relevent or not), but at some point ages ago the fuse blew for the fan - the 25A (iirc), fuse in the engine compartment fuse box.

Cheers,
Phil.

[rovamota]

Where is the fan relay located.

Kev.

[soberphil]

Not sure, haven't tracked it down yet - under the dash drivers side?

I'll have a look in the Haynes manual later, though I seem to think I looked in that previously and it wasn't much help.

[soberphil]

Can anyone tell me what happens in a BRM when you disconnect the brown coolant temperature sensor while the engine is running?

I believe the fan should start (so watch where you have your hands - careful!), but what I'm really interested in is whether the fan stops when you reconnect the sensor?

Also what does the wiring loom look like where the wires from the brown temp sensor joins the rest of the loom? On my car it has a slightly non standard appearance to it - involving electricians tape - I'm wondering if it has been messed with or if this is the factory look!?

Many thanks!

Phil.

[rich brm]

my fan stays on as well about 10 seconds after start up does this effect the car in anyway?
thanks rich

[soberphil]

If anyone is interested I have concluded that this is a wiring problem.

My reasons are thus:

When I changed the termostat the problem disappeared, leading me to think the stat had been sticking, but the problem recurred, another stat, and again the problem recurred.

I changed the starter motor a few weeks ago and magically the fan problem as disappeared.

I can't see how the starter would have any effect on the fan so I can only conclude that in each of the jobs I've done I knocked some wiring or connectors somewhere and the fan fault has been "cured". How long it will last this time is anyone's guess!