# Radiator Fan Switch????



## kwolfsburgk (Sep 25, 2008)

My 2002 jetta is overheating. The fans kick on sometimes and i replaced the thermostat already. I think it may be a fan switch or relay. Can anyone tell me where these parts are? That would be great


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## BrothaVduBVA (Aug 19, 2010)

ECStunning.com 

I had this problem last year and it was the water pump? 

IS the car overheating at a stop or when it moving. Also have you checked your T-stat???


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## kwolfsburgk (Sep 25, 2008)

Thermostat is brand new. Doesn't Really overheat when not moving


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## BrothaVduBVA (Aug 19, 2010)

are you getting any coolant flow back into the coolant bottle. Have you ever changed the pump before? also How many miles do you have on your VW?


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## kwolfsburgk (Sep 25, 2008)

I know the pumped has been changed but idk when. It is my sisters car but i think about 140k on it. I think it may also be the water pump but was hoping it could be a simple switch or fan relay or something


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## BrothaVduBVA (Aug 19, 2010)

My symptoms were: Overheating while driving, I overheated at idle but that didnt happen til we let it run for an hour trying to bridge the fan switch with a paper clip. After spending money on fan switches, radiator fan switch relay I had spent about 120.00. In my case I had a plastic impellar on my pump which the impellar wanst attached to the pump( at idle and low revs the pump functions, but at engine strain and high RPMs it does not turn. When I remvoed my pump the plastic impellar collapsed in about 100 peices. I know its a pain in the ass but its most likely the cause of the problem. If you remove the t-stat and coolant flange, stick a finger in the hole and feel if the pump its either metal or plastic. When I did this I realized my coolant pumps impellar was loose and moving and made of plastic. The only way to tell If the pump is bad, is to either take it out, or observe if the coolant is being cycled around the system. I did this by removing the coolant return line from the top of the coolant bottle. If coolant comes out the line when the t-stat opens then you have flow. If you do this be careful I sprayed hot coolant everywhere, so wear some work glasses or something.


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## slowbluVW (Oct 15, 2002)

kwolfsburgk said:


> My 2002 jetta is overheating. The fans kick on sometimes and i replaced the thermostat already. I think it may be a fan switch or relay. Can anyone tell me where these parts are? That would be great


 The fans kick on sometimes? In the summer, they should cycle on and off regularly if the AC is off, especially at idle. With the AC on, they should run continually as long as the AC button is pushed in. Fan failure on MK4 VWs is common now that they are getting up there in age. 

I had to replace my "large" fan last year because it would lock up from time to time and the car would run hot when the AC was on (and the AC compressor would groan from a lack of proper airflow through the condenser). I got a new fan from germanautoparts.com and all has been well ever since. 

A quick check to see if your fans are working is to open the hood and turn the AC on. Both fans should be running in either low or high speed depending on how hot the coolant is in the radiator. Bottom line, both fans should be on. If not, smack the fan motors with a screwdriver handle or small hammer to see if they come on and also check the fuses under the cover on top of the battery box. 

If the fans run with the AC on but do not cycle with the AC off, your fan temp control switch is probably bad. This is what tells the fans to kick on and at what speed. It is on the bottom driver side of the radiator, a few inches from the bottom. Another fairly common problem on MK4s as they age. There's also a fan control module that is known to go bad-the fans plug into this module. 

It could be the water pump, but since our cars use electric fans to cool the coolant, you have to make sure the fans and the respective electrical system is working properly first.


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## blue.mike (Jun 8, 2011)

i have the exact same problem on my 2005 jetta 1.8t.

i JUST ordered the rad fan thermo switch and wil install it as soon as it gets here. hopefully that fixes the problem and its not the fan control module.

im a little worried about the way the coolant is flowing in the reservoir though. with the car running at normal temp and the reservoir cap off, the coolant just bobs up and down until it actually overflows... when i turn the car off... the reservoir is practically empty!?

also, when the problem first started happening, only one of the fans actually turned on when the a/c was switched on, i played with the wires and hit the fan with a pry bar a little and drove it around the block and next thing i knew both fans were running.

thnks slowbluVW very informative post, and everyone else of course for their input :thumbup:


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## BrothaVduBVA (Aug 19, 2010)

I replaced all the above components you all have mentioned. but the bottom line is, if the pump doesnt circulate the coolent past the fan switch the fans WILL not cut on. At least they didnt in my case, and I replaced the fan switch, radiator fan switch relay under the battery box, and the entire fuse box on top of the battery, and i brought test fans froma junk yard for 50 beans. total cost in parts that did nothing 220.00. i spent that again on a complete water pump kit at ECS, hell for 350 u can get a complte coolent pump kit with everything needed and a pulley kit, which makes it easier to install with everything off. In the end I wish I had enough balls to just take the pump out from jump street. But like I said, if the pump is failing the coolent is not circulated, which doesnt hit the fans switch, which doesnt force the fans to cut on, and draws the air across the radiator. Im going to ask u a question ps2375 asked me, what comes before the thermostat and fanswitch?


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## blue.mike (Jun 8, 2011)

so i changed the rad fan thermo switch. and still does the exact samething its been doing. i jumped the wires at the connector testing the motors at low and high speed and when the connector is bridged; the fans go on without a problem. did i get a faulty sensor
or is this determine my problem is caused by the rad fan controle module.

from what i can see, there is flow at the top hose hooked up to the coolant reservoir when engine is at operating temp. but the flow is not very constant and it flows a lot more when i rev the engine.
waterpump


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## BrothaVduBVA (Aug 19, 2010)

dude, I brought three different fan switches, and I had the same result you had, except my coolent was not circulating. In my case, my motor was boiling over. I know its a pain, but if you cant remember or there is documentation when the TB and pump were changed its time to do it cuz O. the most you have to loose is 2 days, well you could break it down and put it back together in 6 hrs, there no reason, besides not having THE RIGHT TOOLS you could have it back on the asphalt in the same day.


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## nrotteveel (Jan 27, 2015)

Do all of you buy OEM equipment to replace these parts? I have to check my system since my large fan doesn't turn on, but the small one does. So if it is the large fan, have you guys all used the OEM part for $$350-400 or do you buy an aftermarket. Given this is just a fan, I was looking at an aftermarket fan since it is half the price. But wondering what people have found.

If it is the temp fan control sensor, I will go OEM. But does everyone recommend that the OEM FCM be used or have folks used some of the aftermarket. For the electronics I typically stay OEM, but wanted to hear what people have used and if they have been any success or failures with aftermarket. Thanks


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## dogdog (Jul 26, 2007)

None of the parts I replace is OEM.... there are a lot of parts I replaces on my MKIV especially thing made out of plastic. and including this fan switch at the radiator, I got this from autozone, because it is convenient . needs a large 27mm or 30mm socket though.... If you think OEM is what you needed by all means.... other parts I can wait I just order online cheaper.

The FCM I got is from GAP and the 2nd one is from rockauto or ebay.... still none if it is OEM.


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## arubio1 (Jun 5, 2014)

BRINGING THIS BACK FROM THE DEAD. So my 1.8t awp is overheating. The radiator fan is new (only works with a/c on), new water pump, timing belt, rollers, radiator, radiator lower hose, temp sensor (from the dealer), and Thermostat (durmast). It overheats at highway speed but! my question is, would this be because my fan doesn't kick on without the a/c on? or could it be the thermostat? I don't wanna say its the pump because this was a problem before i got it changed and i got it changed literally 2 months ago (water pump). I don't mind spending the money on OEM parts but i wanna get an idea what i need to buy to fix it


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## Anony00GT (Mar 6, 2002)

Yes check the water pump. You can pull the thermostat and stick your fingers in the hole to feel the impeller.

Water pumps on these are the one place you DO NOT want to to OE. Get an aftermarket one with a metal impeller.


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## dogdog (Jul 26, 2007)

thermostat or radiator fan switch?

if your car is overheating at highway speed, coolant is not passing through the radiator to be cooled. Unless you blocked the front of the car with cardboard, dead body of some type or really dirty radiator for some reason.

if you suspect it is the thermostat. you can always do that boil the water dip in thermostat see if it opens trick to test it. or check if both top and bottom hose of the radiator is hot... if they are most likely your thermostat is fine (though some times it could be partial open)... and your water pump or something else is blocking the flow ...maybe time for a flush ?

Not sure about fingering the impeller though.... :laugh::laugh::laugh::laugh::laugh::laugh::laugh::laugh: mine is pretty far away from the water pump... or at least something I think it is a water pump.


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## arubio1 (Jun 5, 2014)

any suggestions on metal impeller water pump brands??


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## dogdog (Jul 26, 2007)

Didn't you say you just got the new water pump? Even if it is plastic it shouldn't fail that fast.
Maybe it's time for some triage / flushing / testing some suspected components.


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## arubio1 (Jun 5, 2014)

Well, i did a flush about a year ago, the radiator is about year old as well, i will check the hoses to see if the temps are different but i suspect the thermostat just because its a durlast brand one


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## dogdog (Jul 26, 2007)

arubio1 said:


> Well, i did a flush about a year ago, the radiator is about year old as well, i will check the hoses to see if the temps are different but i suspect the thermostat just because its a durlast brand one


boil it in water and see if it opens ( in pot that you will never going to be use for food of cause)... mine is from rockauto not sure what brand.... it opens .... I just do a water hose flush (both engine and radiator when I change that water pump.... no issue so far..... 
think the thermostat are install one way only, if you fit it the wrong way it would leak or maybe not opening , if you got it reversed maybe.... or a wrong temp range one ? for a $10 part I would change that before re-doing the water pump IMO.


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## arubio1 (Jun 5, 2014)

I didn't get a chance to pull the thermostat (Cause i work m-f) but i did check the hoses. The radiator hose coming out of the block where the thermostat housing is located was almost cold in comparison to the upper hose coming off the radiator that passes through the green top temp sender. Does this mean bad thermostat?


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## dogdog (Jul 26, 2007)

cheapest and easiest is to check the thermostat it could be installed incorrectly maybe backward or defective or one with wrong heat range.


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