Revs drop when fan comes on .95 VR6

[skid 1]

The revs drop dramatically, sometimes to the point of stalling when the fan kicks in on my 95 VR

Couple of mates and a tech suggested that it could be the Yellow temp sender could be faulty.

 

Could they be right or any other reasons could be causing this?

 

I have purchased a new sensor today which is Black to replace the original yellow one at the price of £32.66 inc the "O" ring.

Looks like a right chewy job to get in about and change esp since i have AC hoses.

[skid 1]

No advice on this guys?

[VW_OwneR_85 1]

it could very well be as that sensor does control the temp gauge and the fan control unit,

i replaced mine by swaping them over realy quick, obviously lost a small amount of coolant but nothing major

mine was none AC though, just dont forget to pull the old O ring out aswell.

 

edit: still trying to think why the revs would drop though?

i could imagine the revs dropping if the AC compressor comes on but why would it make a difference if the fans come on? strange, but you brought the sensor so idd get that swapped over first and try it.

Edited August 5, 2012 by VW_OwneR_85

[skid 1]

I thought one of the sensors told the ecu to raise the revs slightly to compensate for the fan going on and drawing more power from the electrics.

My thinking is that one of them is not telling the ECU to do this so once the fan kicks in its drawing heaps of power...................maybe somebody could explain better plz.

[VW_OwneR_85 1]

the fan is electricly driven by its own motor so it shouldnt affect the engines revs at all , the only thing that i can think of that would affect the revs is the aircon compressor as thats driven off the AUX belt and would affect the revs ,

 

edit: only just saw your sentence about drawing more power when fans on,

not sure but all i can say is when my fan comes on theres never any change in engine revs at idle, its allways below 1000,

Edited August 5, 2012 by VW_OwneR_85

[jamiehamy 0]

The fans on the Corrado are fairly powerful and therefore will likely draw a fairly large current when they start, which would put a load suddenly on the alternator, thus causing the revs to drop. This happens with mine but the revs settle almost immediatly.

 

The reason it happens with mine (I think) is a dodgy fan control module, meannig it doesn't work on speeds 1 and 2, therefore only on 3, hence the drop in revs when it comes on. IF it had gone through speeds 1 and 2, there would not be such a large and sudden draw of current.

 

My thoughts anyway :)

[GusPW 0]

My revs used to dip when my stage 1 fan was not working so was going straight to stage 2, was only brief but was worse at night when headlights were also a demand on the alternator.

 

Changed rad temp sensor and it's fine now.

[Stonejag 10]

Try cleaning your idle control valve. My fans only work on stage 3 (join the club!) and there's a noticeable change in engine note when they kick in. What should happen is:

 

1) the temperature-switch half of the yellow sender clicks on to run stage 3 fans

2) A relay somewhere (probably not the fan-controller, as the yellow sender is supposed to be the 'help, my fan-controller's failed) turns the fans on.

3) The fans start up, which draws a lot of current. Remember there's a 20A fuse on the fan controller!

4) Remember that the dynamo running your push-bike's lights spins freely until you flick the switch: then it puts more resistance on the wheel and you have to pedal faster to keep the same speed. Same principle applies for the alternator - the more current it has to supply, the greater the resistance to being turned it will put on the accessory belt.

5) Increased resistance on the accessory belt means the engine has to work harder to maintain the same output.

6) There should be a very short delay as everything works itself out, but the engine revs will rise to meet the new demand on engine power without stalling.

 

If 6 doesn't work properly it's a sign that everything before that point is behaving as it should and it's a problem with the engine not recognising when it has to increase the revs when it's being worked harder. The fans may not be working properly (in which case the sender in the radiator is a good place to start - bridge either terminal to the centre and you should get speeds 1 and 2, if you don't then try the fan controller) but if your engine's stalling when the fans come on then it should also struggle when you suddenly turn on all the lights, rear window heating etc etc.

 

Stone

[skid 1]

Could someone explain the fan stages?

How would I know the differance between stage 1... 2... 3?

[GusPW 0]

Have a read of the vr6 cooling thread in the engine bay forum. It should all be in there on first post.

if you try the fan speed tests it mentions you'll then know the difference.

 

Basically though if it's very noticeable from inside the car then it's stage 2 or 3

[Kevin Bacon 5]

If speed 3 kicks in, the voltage drops to 10V until the alternator can catch up, which definitely drops the revs.

 

Not even modern engines cope with huge voltage drops without a slight hiccup, so I wouldn't worry about it too much unless it does stall, but if speed 3 is coming on, it's normal for that to happen.