# R32 thermostat



## Rallyaudis34 (Aug 2, 2015)

The fan is not kicking on and causes over heating. Which thermostat switch should I get and is that the problem?


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## Eric D (Feb 16, 1999)

No need to replace the thermostat temperature, the stock one is fine.
By design the VR6 has a low coolant flow, this was done for emissions reasons.
You'll get very poor fuel mileage if you switch to a cold thermostat.

The fans on the Mk4, unlike those used in the Mk1, Mk2 and Mk3 has cooling holes in the motors case.
These are not used in the early models and those fans have little issues, save for the Mk3 which had a recall for improper materials.
The Mk4 holes allow road debris to enter the motor causing damage to the armature. I've replaced more Mk4 and newer generation fans, than I have the older ones.
This is called forced obsolescence, meaning the part only has to last as long as the original warranty. Sure you can argue that the fans are more efficient because the motors are smaller, but I will counter that the old ones are still working . The old ones are 20, 30 and 40 years old, and I've been replacing fans on newer models within 4 years of its production date.
The other reason for the early ones lasting longer has to do with the wire gauge size used. Older models had thicker wires, where the new cars are much thinner, its gone down every generation.

Mk4 has issues with melting fuse boxes, the one located on the battery. 
The failure is caused be dissimilar metals used, the bolts and nuts, fuse strips and the stamped steel used for the buss bar and ATC fuses.
All the failures I've seen happen at the body wiring side, the side with the darker color nuts.
The buss bar side rarely melts unless power to the circuit wasn't cut, or the wire is frayed where its crimped or a loose connection at the battery post.
The ATC fuses will melt the plastic too.

In case you are wondering why VW uses "S" to describe the fuse location, it has to do with the fact its a German word *S*icherung meaning fuse.











In this pic, you'll see S164, the fuse strip is blown and look carefully at the wire itself. Its oxidized and this will cause an increase in resistance, thus leading to voltage drop or higher current draw.
Notice the adjacent wires are bright copper and there is no discoloration of the wires plastic sheathing.
This is the wire for your fan control module, and the damage warrants a repair by removing the damaged section or replacing the entire wire. VW won't sell your this single wire in the same color (repair wires are yellow) but will sell you a harness if you want it. Most techs will cut our the damage and repair the section unless the damage is found throughout the entire length.











In this example you'll see S180 is burnt. This damage warrants replacing the fuse box.
This is the cooling fan fuse.











Keep in mind that even though these fuse boxes look the same for other Mk4 cars, they have different part #s.
What isn't told and I had to search for awhile is the amperage rating, with the R32 having the highest amperage rating of the Mk4 vehicles.
The other ones having the same high amperage are service vehicles (Police/fire/taxi). 

If you have a Mk5 R32, the fuse box isn't a issue, but the fan motor has a fan control module built it.
This module faces the radiator which is the hottest side and the reason for its early demise.


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## Pitchwayne (May 3, 2014)

Eric D said:


> No need to replace the thermostat temperature, the stock one is fine.
> By design the VR6 has a low coolant flow, this was done for emissions reasons.
> You'll get very poor fuel mileage if you switch to a cold thermostat.
> 
> ...


Do you have any idea why on my mk4 12v, (which already has a new radiator switch on the bottom driver side of the radiator) the fans wont turn on? It overheated and maxed the temp gauge when I just let it idle for 10 minutes

Sent from my LG-E980 using Tapatalk


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## Eric D (Feb 16, 1999)

Pitchwayne said:


> Do you have any idea why on my mk4 12v, (which already has a new radiator switch on the bottom driver side of the radiator) the fans wont turn on? It overheated and maxed the temp gauge when I just let it idle for 10 minutes
> 
> Sent from my LG-E980 using Tapatalk


Yes I do, but I hope you have a Bentley manual because the information for troubleshooting is there.
The troubleshooting guide in Chapter 19 will help you isolate the issue.

If you didn't get a Bentley for one the several December holidays, fear not the manual is still available. Shop around for the best price and ideally you'll get the hard back book, the soft cover like I have will tear its spine, it won't if you don't read it. :laugh:


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## Pitchwayne (May 3, 2014)

Eric D said:


> Yes I do, but I hope you have a Bentley manual because the information for troubleshooting is there.
> The troubleshooting guide in Chapter 19 will help you isolate the issue.
> 
> If you didn't get a Bentley for one the several December holidays, fear not the manual is still available. Shop around for the best price and ideally you'll get the hard back book, the soft cover like I have will tear its spine, it won't if you don't read it.


Ill go grab one. Do you have any personal thought you think it may be? Fuses are also good.

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## Eric D (Feb 16, 1999)

Pitchwayne said:


> Ill go grab one. Do you have any personal thought you think it may be? Fuses are also good.
> 
> Sent from my LG-E980 using Tapatalk


Yes, it will be an issue with one of the various components in the cooling system.
Since I don't have the car in front of me with a work order, I will say it will be an issue with an electrical/mechanical failure.
I know you want a specific component but it doesn't work that way, troubleshooting is required to identify the exact location of the fault.

With the Bentley manual and its specifications for various sensors and components you can isolate the problem and replace just that part.
No need to throw money at everything you suspect, troubleshooting require specific tools some that will make the job faster but will cost some money.

I have factory break out boxes that allows me to test a vehicles harness easily.
I also have a Power Probe 3 with ECT-2000 wireless detector, this tool will allow you to find the exact location in a wiring harness for an open circuit or short. The old way of doing it with a DVOM will not pin point the issue, you'll be cutting tape, or removing the complete harness in an attempt to find the fault, then you'll be probing other wires in the same harness for shorts to that other wire you suspect. Its time consuming, but truthfully this power probe is less than 2 hours labor at the dealer. You can find it online for less than $200.
http://www.ebay.com/itm/Power-Probe-PPKIT03-Master-Kit-w-Gold-Leads-and-Short-Finder-/261332296620


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