Radiator Fans Will Not Come On !

touaregv10tdi

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Bettle 2001 TDi ALH. Question for the experts. My Radiator fans are not coming on when the engine is hot.
The fans come on when I turn the A/C on , that rules out the fans themselves being burned out.
I have replaced the thermo swith on the bottom left side of the radiator, Fuses are good, ( Included the ones on topr of the battery and the driver's kick panel ) yet the fans will not come on when the engine reaches normal operating temperature.
Any hints ? Next I will check the connectors under the battery .
Please let me know if any of you has experienced this issue before.

Thanks.
 

steelmb

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Have you used Scan Gauge or VCDS to read the actual temp of the engine. Is the engine over heating? The fans will only come on when the engine temp cannot be maintained at opperating temp by the water pump and rad alone.
 

touaregv10tdi

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Thanks for the quick response. I have not checked the actual temp via VCDS. I will do it this afternoon when I get home. I drove the car for 10 miles , parked it on my driveway idling for 15 minutes and the fans did not come on. I thougt it should have after a 10 mile drive, but yes I will check the temp today. Thanks again.
 

steelmb

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jcrews said:
Low speed is 94C and high speed is 105C. The thermostat is 87C. My fans rarely turn on; it has to be very hot out.
Thanks jcrews. I couldn't remember the temps they operated at but since the OP was not complaining of overheating I am thinking all is fine with his car.
 

DanG144

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Yes, even dragging a trailer down the interstate in August, the fans would not come on.

Even when comming off the interstate directly to a rest area.

Though I would slow down to 60 mph over the last mile, if traffic allowed.

But even when I did not slow first, the fans never came on.

And I did verify that they work, from all signals.
 

touaregv10tdi

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Temperature.

Awesome guys ! Thanks. I will drive it today for few miles. Park on my driveway again , hook up my VCDS to it and monitor the temp while it idles and see if the fans come on.

:D
 

DanG144

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I am now seeing some ALH cars which do a VCDS output test to verify that the ECU can run the fans. I am not able to figure why some have it and some do not.
I do not remember seeing that on any ALH cars a few years ago.
All PD's that I have run across do have ECU fan tests under the Engine Module, Output Tests.
 

touaregv10tdi

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Oh, cool , that is good to know. I will check my VCDS. I was afraid of overheating the engine, but I believe if it does, I will get a Red temp icon on my Dash. ( yeah the beetle 2001 does not have a gauge per say ) the temp icon lights up, or flashes depending on the issue you are having.
 

touaregv10tdi

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Radiator fans

:confused: I am kind of puzzled now. I replaced the radiator thermo switch and the coolant temperature sensor on the block. I have monitored the temp on VCDS , it got to 101C and none of the fans came on...:confused:
What gives????
 

oilhammer

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There are just too many to list....
So, why do you think the fans should come on when the coolant is at 100 C ?

I had an ALH running in the shop today, after a test drive, I know it was fully warmed up, and it sat and idled quietly for about 25 minutes as I was checking some [unrelated] things and I am pretty sure its fans never came on either (I was under the hood) yet it never 'overheated'.

The NB's temp lamp will flash red if it gets too hot. And that will happen in a hurry if the cooling system is not working, like when the plastic water pump impeller tooefs.
 

fnjimmy!

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touaregv10tdi said:
Bettle 2001 TDi ALH. Question for the experts. My Radiator fans are not coming on when the engine is hot.
The fans come on when I turn the A/C on , that rules out the fans themselves being burned out.
I have replaced the thermo swith on the bottom left side of the radiator, Fuses are good, ( Included the ones on topr of the battery and the driver's kick panel ) yet the fans will not come on when the engine reaches normal operating temperature.
Any hints ? Next I will check the connectors under the battery .
Please let me know if any of you has experienced this issue before.

Thanks.
The fan won't come on simply because the engine is at operating temperature, that would be a poor design. The fan will only come on automatically if the temperature in the radiator itself is greater than specified. Turning on the A/C activates the fan to cool the A/C condenser regardless of the temp of the radiator. I don't think you can check radiator temperature with VCDS but I could be wrong.
 

mctdi

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touaregv10tdi said:
:confused: I am kind of puzzled now. I replaced the radiator thermo switch and the coolant temperature sensor on the block. I have monitored the temp on VCDS , it got to 101C and none of the fans came on...:confused:
What gives????
The temp sensor for the dash gage and ECU are together in the one unit, at the coolant outlet of the cylinder head.

The temp switch for the fans is in the second half of the radiator near the outlet. Coolant flows from the driver's side to the passenger side in the top half of the radiator, in the right header from the top half to the lower half, and across the lower half to the outlet header on the driver's side with the fan temp switch.

So the whole radiator has to be HOT before the temp. switch will trip.
 

AndyBees

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FYI, looking at the car from the front, on the battery fuse panel, the left green 30 amp fuse is for the two fans out front... the other two green 30 amp fuses are for the ABS system. I've seen the Fan fuse creamated on more than vehicle!

Last July I worked on a 99 NB with fan issues... corroded fan motors. Anyway, after putting everything back together, the engine idled for almost 35 minutes before the fans come on! I observed the temp with VCDS during the process. As I recall, the fans kicked in according to spec and off according to spec.

The Fan Control Module could come into play with this issue. I'm not sure if it either works or is dead or maybe can work with the AC mode and be faulty with the engine cooling mode?

Right now, the fans don't work on my 2000 Jetta in the AC mode. I have "hot" wired them and they work fine. No fuse issue. So, it's either the Fan Control Module or a connector somewhere that's corroded! I will ferret the problem in the next few days!
 

Dimitri16V

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the fans are wired in a parallel configuration to the FCM so even if the FCM bites the dust the fans will still come on to protect the engine
 

touaregv10tdi

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oilhammer said:
So, why do you think the fans should come on when the coolant is at 100 C ?

Also Jcrews mentioned :
(Low speed is 94C and high speed is 105C. The thermostat is 87C. My fans rarely turn on; it has to be very hot out.)

Thanks for the input Oil. I was going by the temperature range the manual says the fans should come on.
I hooked up my VCDS and none at fans came on at 100C/212F
 

oilhammer

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There are just too many to list....
Yes, the fans come on when the coolant at the fan switch in the bottom of the radiator left tank hits 100 C, the coolant temp you see in the engine or intrument data is taken from the coolant temp sensor in the water neck on the cylinder head.

If the engine is not overheating, your red coolant lamp never comes on flashing, then motor on, your cooling system is working well enough that it rarely will need the fans anyways (like NORMAL on the ALH engine).
 

touaregv10tdi

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Thank You !

Thank you oil.
Your advise is always welcome. One of these days I will stop by jut to thank you in person, I am in Wentzville.
For others TDiers reading this , I am just few miles away from Oilhammer.
 

fnjimmy!

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touaregv10tdi said:
Thank you oil.
Your advise is always welcome. One of these days I will stop by jut to thank you in person, I am in Wentzville.
For others TDiers reading this , I am just few miles away from Oilhammer.
One thing you might consider is to ask whether you have a problem before you go about trying to fix a problem you don't have. These cars have some inherent differences to conventions that many people take for granted.
 

123jetta

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02 jetta tdi
can anyone help. im having the same problem,
vw tdi jetta ,
fans only come on when A/C is turned on, i jumped them yestday so the fans stayed on whole time while driving , well the dam jetta over heated again


i test the water pump is working
new cooling fan switch senor
and both of the fuses are good
and both of the fans wook so what can i test or do now?
 

123jetta

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tested waterpump by take the line off back of the expansion tank , and running the car . it has a constant flow ...
the heater in the car is hot and works fine ..
 

123jetta

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the car wont overheat when idling(190). starts overheating when driving , even with the rad fans on high and the inside heat turned on high
 

oilhammer

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There are just too many to list....
Yeah, you still have not answered my question. :(

Overheating... ? Does this mean the temp gauge goes up? Does the engine start boiling over and spewing coolant out the pressure relief channel in the cap/bottle? Is there pressure building up in the cooling system? Has there been a loss of coolant? Have you compared the coolant temp value with a scan tool on both the Engine and Instrument sides?
 

123jetta

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i haven't let it get that bad yet , i just see the temp gauge go up to 230 240 and pull over , and it cools down
 

oilhammer

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There are just too many to list....
Well I would want to verify with a scan tool that the gauge value is correct, although the sensors fail commonly they usually do not fail like that.

A thermostat is a possibility, although those rarely ever fail closed either, but it is possible, especially if it is some unknown Brand X one installed by someone.

The other possibility is that the radiator itself is plugged up, and that is rare, and would usually result in a plugged up heater core first.

You can feel both the radiator hoses once you've been driving it a bit, they should both be warm to the touch if the coolant is flowing. ALHs need very little cooling unless you are under a load on a really hot day for a sustained period. They are so efficient they just do not make much waste heat.

I'd try a thermostat first. Get an OEM one from the dealer or a Behr or Calorstat brand. And I would get an OEM neck and o-ring too. Quick and easy anyway, and while you have it off you can physically verify the water pump impeller is attached and working, too.
 
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