Engine fan draining battery help

[boombastictiger]

On my 1.8t Passat, after it is switched off one of the fans in the engine bay comes on and off intermittently. This caused the battery to die after a few hours so i called breakdown out and he didn't have a clue what it could be! The engine light was on so he reckoned something to do with this. The fan is not for the radiator and has a loud hiss which comes from near the turbo but seems to be behind some covering so cannot see it.

Does anyone have any ideas what it could be?

Thanks

Sk

[IanCress]

First thing i'd do is to get that code read. A fan and a hiss makes me think it's air-con, however it wouldn't run with the engine off. What other fans do you get in the engine bay!?

[boombastictiger]

IanCress said:

First thing i'd do is to get that code read. A fan and a hiss makes me think it's air-con, however it wouldn't run with the engine off. What other fans do you get in the engine bay!?

Going to the garage in a bit hopefully the code will show the source. I am not sure if there is a turbo fan as thats where the it comes from and it is defo not the engine fan.

[swisstoni]

I was recently parked next to a Mercedes doing exactly the same thing.

[Matt_N]

1.8T have two fans near the radiator, one for the main engine cooling and one for air con cooling, most problems with these cars come in the form of the fans either pulsing on and off or only working on one speed but as far as I know this only happens when the engine is running and is due to a failed relay.

The only other fan type unit I can think of in the 1.8T is the secondary air pump which runs at start up for a while to speed the cars warm up cycle up to reduce emissions, it could be that?

[andy-xr]

My guess, just purely based on limited info is that you have a water leak (hiss) that's causing overheating and the fan stays on to try and cool the car down once stopped. Why it would do it for so long though is another matter, it'd need to have a constant power supply regardless of ignition which I'm not sure an engine fan always has.

[thatdude]

I'm going to go with a failed relay sticking on (have you noticed any trend e.g if its been wet or anything like that?)

My wife had relay problems and her wipers were getting ever such a wee bit of power to them, making them creep slowly across the windscreen. I had a starter relay on my motorcycle stick on so the engine kept turning over even when turned the ignition off.

[boombastictiger]

thatdude said:

I'm going to go with a failed relay sticking on (have you noticed any trend e.g if its been wet or anything like that?)

My wife had relay problems and her wipers were getting ever such a wee bit of power to them, making them creep slowly across the windscreen. I had a starter relay on my motorcycle stick on so the engine kept turning over even when turned the ignition off.

Not really, it was yesterday afternoon, that it started happened, and when it was being driven as well it sounded like it was coming on. I think the weather was just the grey clouds and a bit a rain.

andy-xr said:

My guess, just purely based on limited info is that you have a water leak (hiss) that's causing overheating and the fan stays on to try and cool the car down once stopped. Why it would do it for so long though is another matter, it'd need to have a constant power supply regardless of ignition which I'm not sure an engine fan always has.

When the fan comes on, it spins and as it speeds up its a very high pitch squeak/hiss. Bear in mind the fan is intermittent when engine is off, so something is telling it to come on and off.

Matt_N said:

1.8T have two fans near the radiator, one for the main engine cooling and one for air con cooling, most problems with these cars come in the form of the fans either pulsing on and off or only working on one speed but as far as I know this only happens when the engine is running and is due to a failed relay.

The only other fan type unit I can think of in the 1.8T is the secondary air pump which runs at start up for a while to speed the cars warm up cycle up to reduce emissions, it could be that?

The fan is packaged on the left hand side of the engine and enclosed within the turbo housing so I can't see it, but can hear it and feel the air at the bottom. It is defo an electrical fan. It actually sounds like maybe the air con cooling or secondary air pump?

Edited by boombastictiger on Friday 27th February 09:54

[Matt_N]

Does it look like a black plastic turbo?

If so that's the secondary air pump, don't think I've heard of them running on their on accord though.

[benharris]

I had this several years a go on a Volvo 480. The radiator fan wiring was effectively connected direct to the battery, with no ignition based relay control, so that the fan could continue to run after the the ignition was switched off. It also had an electric water pump so that water would continue to circulate until cooled down, but that's beside the point!

The sensor for controlling when the fan would run was screwed directly into the radiator and was a waxstat switch (similar in operation to a thermostat). In my case, when it failed, it failed in a 'make connection' state - not a 'break connection' state, causing the fan to permanently run until the battery died.

It might be something as simple as this - worth checking if you have any sensors connected coming directly out of the radiator. If you have, and unplugging it stops the fan, then you've found the problem!

EDIT - just realised you said it's not a radiator fan, so my post is probably wrong. Might still be worth a check though!

[boombastictiger]

benharris said:

I had this several years a go on a Volvo 480. The radiator fan wiring was effectively connected direct to the battery, with no ignition based relay control, so that the fan could continue to run after the the ignition was switched off. It also had an electric water pump so that water would continue to circulate until cooled down, but that's beside the point!

The sensor for controlling when the fan would run was screwed directly into the radiator and was a waxstat switch (similar in operation to a thermostat). In my case, when it failed, it failed in a 'make connection' state - not a 'break connection' state, causing the fan to permanently run until the battery died.

It might be something as simple as this - worth checking if you have any sensors connected coming directly out of the radiator. If you have, and unplugging it stops the fan, then you've found the problem!

EDIT - just realised you said it's not a radiator fan, so my post is probably wrong. Might still be worth a check though!

Thanks Ben and everyone. Turned out it was a faulty sensor of some sort for the cooland/engine. Replaced and now working fine £30 job.