Engine Compartment Fan Query

[teeerex]

Hi,

I know this topic has been done to death and I've searched for as much info as I can find on this excellent site. However, I would like to know why my engine compartment fan turns on without fail and refuses to turn off, when my coolant temperature reaches what I believe to be 'normal' - ie needle dead centre.

Car : 996 - MY1999 UK Spec -GT3 Aero with Row030.

I have personally replaced the coolant tank with the latest model and latest cap - after the previous one split. I used Porsche antifreeze with a 50:50 mix of distilled water to fill the system afterwards.

Coolant levels are static,

Purged/Burped for a couple of weeks now,

No water in the oil,

Compartment fan draws air 'in' as normal.

Oil/Filter recently changed after 2nd track day.

Front Rads have been jet washed clean with the front bumper / AC Condensors removed - both front fans work fine - they do not cut in until I have been sitting in traffic for 10-15 minutes (ie normal)

If I turn the ignition off and restart the engine then fan comes back on after a few minutes and again, fails to go off - this can happen with 'normal driving', motorway normal driving or heavy track day driving. Throughout all of these scenerio's the temperature remains at a perfect top dead centre, or slighly over in traffic. (which I believe is 'normal')

I think I've covered all the 'try this' suggestions from this website so believe it to be a faulty temp sender to the fan - is this feasable ? Has anybody else experienced this ? Could it be the 'Aero' kit restricting air flow ? (I notice that the only route for hot air to escape unassisted is via the fan shroud - is this enough ?)

I'm tempted to just unplug it, but know I shouldn't ! (assume I'll get a warning light anyway...)

Has anybody got any further ideas ?

Many Thanks in advance,

Richard.

[1999Porsche911]

Could be a bad sensor. Remove it and measure the resistance. Also, by design, the fan will come on when the engine reaches operating temperature if the cable is not solidly connected to the sensor. Check the connection. Air flow is not a problem as I have the same setup as you do. Mine seldom comes on and only when sitting in direct sunlight on 100F temps.

Edited November 29, 2005 by 1999Porsche911

[Loren]

Two things come to mind. One is that the water level sensor (in the coolant tank) sends a message to the cluster (and DME) to turn the fan on. I would think if this were the case then you would also see a flashing coolant warning light.

Secondly, there is a relay that turns on engine compartment purge fan. The relay is in position 8 (part number 141 951 253 B ) on the DME relay panel.

[teeerex]

Excellent - thanks 1999Porsche911 and Loren - I'll post the outcome ... :-)

[teeerex]

Excellent - thanks 1999Porsche911 and Loren - I'll post the outcome ... :-)

Update : I've checked the relay's - They don't seem to be numbered (?) so checked all the relays matching that part number (4) - VW Part btw.. - All had a coil resistance of 68 Ohms, all N/O contacts were open ie no stuck contacts, and all operated normally closing the contacts when +12v applied to the coils. I guess it's not those then...

Sender unit on the coolant tank was replaced when I did the tank - double checked the connection there and looks good.

Temperature sender in the engine bay - er.. where is it ! I think I've spotted the main coolant sender (pic attached) and another 'sender' type component with two wires coming from it (both attached) but can't see anything obvious that monitors the 'air' temperature in the engine compartment ?

Thanks for your help so far ...

[1999Porsche911]

The lower picture is of the sensor. It slides out to the right to remove. Unplugging it on a warm engine should activate the fan immediately.

Edited November 29, 2005 by 1999Porsche911

[teeerex]

The lower picture is of the sensor. It slides out to the right to remove. Unplugging it on a warm engine should activate the fan immediately.

Ok Thanks - but I'm a tad confused now. Are you saying this sensor monitors both the air temperature of the engine compartment AND the coolant temperature ? (it does have 4 wires I have noticed). If so, how can it monitor the air when it's almost at the bottom of the engine - surely the sensor should be at the top near the lid ? (not that I'm doubting you - just doesn't make much sense..) Also, I assume if I replace the whole sensor - I'll need to catch the coolant as I assume I'll make a hole in the block when removed !

Thanks - almost there I think ...

Richard.

[teeerex]

The lower picture is of the sensor. It slides out to the right to remove. Unplugging it on a warm engine should activate the fan immediately.

Ok Thanks - but I'm a tad confused now. Are you saying this sensor monitors both the air temperature of the engine compartment AND the coolant temperature ? (it does have 4 wires I have noticed). If so, how can it monitor the air when it's almost at the bottom of the engine - surely the sensor should be at the top near the lid ? (not that I'm doubting you - just doesn't make much sense..) Also, I assume if I replace the whole sensor - I'll need to catch the coolant as I assume I'll make a hole in the block when removed !

Thanks - almost there I think ...

Richard.

Further update - I called Porsche East London to find out the cost of the engine coolent thermostat (£11.27 btw) and they advised that there is a 2nd sensor as I suspected called the 'Ambient Temperature Sensor'. (Great service from Porsche East London parts department - thumbs up) It is located in the plastic inlet manifold on the right hand side of the engine. I've been told that it sometimes pops out of it's mounting and causes this problem. Reseating it should solve the problem. This sensor is only £14.71 but they said they haven't ordered one for 3 years so sounds very reliable. I'm at work at the moment so will check this tonight and report back ... Hopefully this is the problem ...

Cheers,

Richard.

[1999Porsche911]

The lower picture is of the sensor. It slides out to the right to remove. Unplugging it on a warm engine should activate the fan immediately.

Ok Thanks - but I'm a tad confused now. Are you saying this sensor monitors both the air temperature of the engine compartment AND the coolant temperature ? (it does have 4 wires I have noticed). If so, how can it monitor the air when it's almost at the bottom of the engine - surely the sensor should be at the top near the lid ? (not that I'm doubting you - just doesn't make much sense..) Also, I assume if I replace the whole sensor - I'll need to catch the coolant as I assume I'll make a hole in the block when removed !

Thanks - almost there I think ...

Richard.

Further update - I called Porsche East London to find out the cost of the engine coolent thermostat (£11.27 btw) and they advised that there is a 2nd sensor as I suspected called the 'Ambient Temperature Sensor'. (Great service from Porsche East London parts department - thumbs up) It is located in the plastic inlet manifold on the right hand side of the engine. I've been told that it sometimes pops out of it's mounting and causes this problem. Reseating it should solve the problem. This sensor is only £14.71 but they said they haven't ordered one for 3 years so sounds very reliable. I'm at work at the moment so will check this tonight and report back ... Hopefully this is the problem ...

Cheers,

Richard.

I made a mistake. The sensor in the lower picture IS NOT the engine compartment sensor. I didn't look at the picture close enough yesteday to see the coolant hose. That is the temperature sending unit for the coolant. The sensor you are looking for is located on bank 2 (right side of engine) on top, between the middle and back intake shown in the first picture above. It is a 2 wire sensor and your can remove it by sliding ut out towards the right fender. Sorry for the mixup. And YES, it can fall off and sit on top of the manifold, raising the temperature it reads.

Edited November 30, 2005 by 1999Porsche911

[teeerex]

The lower picture is of the sensor. It slides out to the right to remove. Unplugging it on a warm engine should activate the fan immediately.

Ok Thanks - but I'm a tad confused now. Are you saying this sensor monitors both the air temperature of the engine compartment AND the coolant temperature ? (it does have 4 wires I have noticed). If so, how can it monitor the air when it's almost at the bottom of the engine - surely the sensor should be at the top near the lid ? (not that I'm doubting you - just doesn't make much sense..) Also, I assume if I replace the whole sensor - I'll need to catch the coolant as I assume I'll make a hole in the block when removed !

Thanks - almost there I think ...

Richard.

Further update - I called Porsche East London to find out the cost of the engine coolent thermostat (£11.27 btw) and they advised that there is a 2nd sensor as I suspected called the 'Ambient Temperature Sensor'. (Great service from Porsche East London parts department - thumbs up) It is located in the plastic inlet manifold on the right hand side of the engine. I've been told that it sometimes pops out of it's mounting and causes this problem. Reseating it should solve the problem. This sensor is only £14.71 but they said they haven't ordered one for 3 years so sounds very reliable. I'm at work at the moment so will check this tonight and report back ... Hopefully this is the problem ...

Cheers,

Richard.

I made a mistake. The sensor in the lower picture IS NOT the engine compartment sensor. I didn't look at the picture close enough yesteday to see the coolant hose. That is the temperature sending unit for the coolant. The sensor you are looking for is located on bank 2 (right side of engine) on top, between the middle and back intake shown in the first picture above. It is a 2 wire sensor and your can remove it by sliding ut out towards the right fender. Sorry for the mixup. And YES, it can fall off and sit on top of the manifold, raising the temperature it reads.

Resolved ! - Thanks to all - It was indeed the sensor that had fallen off and was resting on the engine block itself.

It fits in the first gap between the first two inlet manifolds on the right hand side of the engine - took some pictures to assist if anybody else has the same problem :-

1. I traced the wires going into the inlet manifolds and pulled out ...

2. I tried to fit it into the holder but found it too tight and didn't want to foce it. Therefore, I took out the sender from the grommit, used some WD40 on the grommit and slid that in first...

3. Then it pushed the sender unit into the grommit from underneath until it clicked into place.

4. A picture of the sender poking it's nose into the air taking the ambient air temperature - as it should be !

Cheers,

Richard.

Edited November 30, 2005 by teeerex

[munro86]

The lower picture is of the sensor. It slides out to the right to remove. Unplugging it on a warm engine should activate the fan immediately.

Ok Thanks - but I'm a tad confused now. Are you saying this sensor monitors both the air temperature of the engine compartment AND the coolant temperature ? (it does have 4 wires I have noticed). If so, how can it monitor the air when it's almost at the bottom of the engine - surely the sensor should be at the top near the lid ? (not that I'm doubting you - just doesn't make much sense..) Also, I assume if I replace the whole sensor - I'll need to catch the coolant as I assume I'll make a hole in the block when removed !

Thanks - almost there I think ...

Richard.

Further update - I called Porsche East London to find out the cost of the engine coolent thermostat (£11.27 btw) and they advised that there is a 2nd sensor as I suspected called the 'Ambient Temperature Sensor'. (Great service from Porsche East London parts department - thumbs up) It is located in the plastic inlet manifold on the right hand side of the engine. I've been told that it sometimes pops out of it's mounting and causes this problem. Reseating it should solve the problem. This sensor is only £14.71 but they said they haven't ordered one for 3 years so sounds very reliable. I'm at work at the moment so will check this tonight and report back ... Hopefully this is the problem ...

Cheers,

Richard.

I made a mistake. The sensor in the lower picture IS NOT the engine compartment sensor. I didn't look at the picture close enough yesteday to see the coolant hose. That is the temperature sending unit for the coolant. The sensor you are looking for is located on bank 2 (right side of engine) on top, between the middle and back intake shown in the first picture above. It is a 2 wire sensor and your can remove it by sliding ut out towards the right fender. Sorry for the mixup. And YES, it can fall off and sit on top of the manifold, raising the temperature it reads.

Resolved ! - Thanks to all - It was indeed the sensor that had fallen off and was resting on the engine block itself.

It fits in the first gap between the first two inlet manifolds on the right hand side of the engine - took some pictures to assist if anybody else has the same problem :-

1. I traced the wires going into the inlet manifolds and pulled out ...

2. I tried to fit it into the holder but found it too tight and didn't want to foce it. Therefore, I took out the sender from the grommit, used some WD40 on the grommit and slid that in first...

3. Then it pushed the sender unit into the grommit from underneath until it clicked into place.

4. A picture of the sender poking it's nose into the air taking the ambient air temperature - as it should be !

Cheers,

Richard.

Fantastic illustrative description. I'm going to run down now just to look and see if that thing is poking up through the manifold!