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Discussion Starter · #1 ·
I have a problem with the cooling fans not turning on when they should. I am monitoring the temp with VAG-COM and the low fan speed will turn on at 100 degrees celsius and at times it will not causing the car to overheat, but at no point will the fans kick into high speed.Here is a list of test I have tried.

Fans kick in low speed when ac is turned on
Fans high and low speed work if connected directly to battery.
Fans high and low speed work by jumping the thermo fan switch.
Checked the fuse connects on top of the battery.

Today I replaced the tempature sensor and thermo fan switch with no luck of fixing the problem. Earlier I was monitoring the car with VAG-COM and the fan would kick in low speed at 100 degrees celcius every time durring idleing, but once I took it for a drive and parked and let it idle the fans never kick in at all then the car overheated. The water pumps is new and is circulating the water. If anyone has a suggestion of what could be the problem please respond.
 

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The fan should not switch to high speed until the temperature of the sensor in the radiator reaches something in the 210-220 degree range. This won't happen if there is not enough flow through the radiator for some reason. Common causes (other than the coolant pump) would be:

Failed thermostat.
Plugged radiator.
Or most likely for the 2.0, air in the cooling system because the purge line is plugged.

See this thread:

http://newbeetle.org/forums/2-0-liter-gas/69386-yet-another-runs-too-hot-thread.html
 

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water pump

sounds like your water pump is not circulating or you have blockage some where. Easy way to find out on the 2.0; drain some of the coolant, remove the upper hose and plastic flange at the motor, you should be able to touch the water pump impeller with your fingers, try to spin impeller and if it turns than you found your problem. Good luck.
 

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Discussion Starter · #4 ·
The water pump was replaced about a year ago with one that has cast iron blades.I forgot to mention that I have replaced the thermostat and while replacing it checked for slack in the blades and the pump seamed fine. Also the return line has water flow when checking.You can tell when the thermostat opens because both upper and lower hoses get warm. Here is my monitoring results from cold to hot, if it helps.

Blue temp light goes out around 55c
Low speed fan comes on at around 100c (which seams a little late)

When the fan comes on at 100c it cools the engine and does not overheat, but at times it does not come on and I have let the car reach 110c before turning off with no fan action at all. Could the fans working intermittently be cause by the FCM?
 

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yep

yep almost everything about the fans and thermal switches go through the FCM. You sure you checked the 30 AMP fuses on top of the battery? I mean put a digital meter on the connector and then wiggle the fuses to make sure you don't lose continuity. well that's the last thing left to check in the system loop-fan control module.
 

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Here is the thread with all the info about the cooling fans:

http://newbeetle.org/forums/questio...3260-summers-coming-here-check-your-fans.html

An intermittent problem is probably the 30 amp fan fuse, leftmost of the three smaller fuses on the panel above the battery. If the fans don't run on low speed when they should be, try wiggling the fuse in its socket. Bad contacts on this fuse are a common problem.
 

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Discussion Starter · #7 ·
I have tested the fuses using a piercing probe at the small wires coming from the fuses, so the fuses and connections are fine. I went ahead and ordered a FCM today. Hope its just bad relay contact causing the intermittent problem.
 

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Discussion Starter · #8 ·
I have replaced the FCM now and followed the "Summer's coming/is here - check your fans!" guide and every thing tested good. Is there anything else that controls the fans other than the thermo switch and fcm module? The thing is every time I start the car up after it sets a little while it will not overheat at idle and the fan kicks in at 100c and cools the engine down then I can take it for a long drive and shut the car off when I park it and its not overheating, but if I park it and let it idle instead of turning it off in a few minutes it will get up to 120c without the fans coming on and be overheating. Its strange that after a drive the fans stop working every time but work at idle. The whole time I am testing I am monitoring the engine temp with VAG-COM.
 

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I still think it could be a circulation problem. The sensor used for the temperature reading is in the coolant flange in the cylinder head whereas the sensor for turning on the fans is in the radiator. If there is not enough flow through the radiator for some reason the radiator will stay below 100C while the temperature reading is higher and the fans will stay off. It could be that the higher RPMs of driving allow enough circulation but at idle there is not enough and it overheats.

A few things to check when the fans don't come on:

Is the coolant still flowing into the expansion reservoir?

Is the air from the heater still just as hot?

Are the upper and lower radiator hoses equally hot?


BTW, has your cooling system ever had green coolant in it?
 

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Discussion Starter · #10 ·
I have water comming from the top return line when I first start the engine when cold and the upper and lower equalize in heat around 100 degrees celcius. I changed the recovery tank cap and the boiling point has raised about 15 degrees celcius. I am wondering if the tank needs to be replaced do to wear and its not keeping the pressure it needs to. Took it out twice tonight and after parking the fans did not work again, but they were kicking on while driving because it would slowly go up to 100 and then quickly go down to 93, then I parked it and the fans would not come on at all. I understand it could be a circulation problem but both upper and lower hoses get hot at around 100 and both heater hoses do to which would not make sense.
 

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"Slowly go up to 100c and then quickly go down to 93c" does not sound like normal operation. The temperature should be steady while driving and the fans should not come on at all. The car moving through the air should be all it needs. Did you have this problem before you replaced the thermostat? Could be a bad thermostat.

Also, the temperature should not change quickly. The only way that can happen is if there is air in the cooling system.
 

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Discussion Starter · #12 ·
Last night I pulled the thermostat and the thermo switch and put them in boiling water on the stove. The thermostat opened each time I put it in the water and closed when I pulled it out, so its not sticking. The new and old thermo switches gets continuity between pins 1 and 2 (slow speed), but never gets any continuity between pins 2 and 3 (high speed),that explains why the fast fan speeds not working but does not explain why the slow is not working after a drive. I am going to pick up another switch today. Also I am going to create a wiring harness to go between the thermo switch and its plug so I can put a fused hot directly from the battery to make sure there is not a short in the harnesses hot wire somewhere which could explain not working after a drive.
 

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The spec on the switch for the fans is stage 1 on between 92-97c, stage 2 on between 99-105c. Your switches are probably both good.
 
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