2012 GTI Thermostat Replacement

Hey Guys,


So I have a 2012 GTI with a suspect thermostat. The water pump itself was last replace towards the end of 2015 under warranty. It is the model that was supposed to correct all the problems, 06J-121-026-BG. The pump has less than 25k miles since it was put in.


The issue I am having is that during driving, the coolant temperature will jump above the 190 mark. When in the past, it has stayed rock steady right dead center. Monitoring the temperatures with a scan tool, I've seen temperatures get as high as 243. At which point, I get concerned and turn the heater on full blast. Running the heater and driving, the temperature will hang around 210 with the scan tool. The gauge will stay dead center at 190 as it always has.


Both of the cooling fans are running. There are no leaks, and I have been monitoring coolant levels with no noticeable changes. Given that the water pump is pretty new, and that I do get heat through the heater core, I figure the thermostat is stuck closed.


So I did quite a bit of searching around this forum, and could not find any threads where someone had replaced the thermostat alone. I know it's buried in the housing attached to the water pump. Is there sufficient access from below to remove the housing and replace the thermostat? I was planning on jacking the car this weekend and taking a look. Probably removing the charge pipe and seeing if I can get to the one housing bolt. If anyone has any insight into replacing the thermostat alone, please let me know.


Otherwise, if I'm going to have to pull the pump, it may be time to look into carbon cleaning at the same time. USP motorsports also sells an all cast aluminum water pump. I would probably install that so I never have to worry about it again.


Thanks.

I'm surprised you have a bad thermostat already, are you sure there isn't air trapped in the system? If I recall, the thermostat actually throws a code and sets the check engine light. At least it did on my 09 with the TSI. I opted to replace the whole thing due to the age of the plastic housing, but you should be good. Sorry I don't know if you can get to it from underneath, I do know access is tight with the manifold.

You'll have to take off the manifold, doing it from under would be a total pain in the ass, especially on jacks.

zrickety said:

I'm surprised you have a bad thermostat already, are you sure there isn't air trapped in the system? If I recall, the thermostat actually throws a code and sets the check engine light. At least it did on my 09 with the TSI. I opted to replace the whole thing due to the age of the plastic housing, but you should be good. Sorry I don't know if you can get to it from underneath, I do know access is tight with the manifold.

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I tried putting the vacuum / purge / fill tool on the reservoir. The system held vacuum just fine for 30 minutes with no leakage. I did this twice. Squeezed hoses, etc. No change.

So, I decided to see if I could get the thermostat housing off without removing everything. Basically took out the air box, charge pipe, throttle bottle, and some various hoses, electrical connections, and brackets.

The housing had two bolts that needed to be removed. One was a torx, and the other a hex. I was able to get the torx off with no problem, but the hex one I had to take a key and lop off most of the 90 degree leg to get it in there. With some work, I was able to get the bolt out. However, there is just a smidgen too little room to get the housing off between the pump and block .

So at this point I can do nothing but remove the water pump. I did this without taking much else apart, leaving the intake manifold on. There is plenty of room to work in there without having to remove it.

With the water pump off, I could see the kit I ordered was incorrect. Somehow, here in Charleston, SC on the east coast, we ended up with a CBFA engine code. This has a special thermostat housing with an electrical connection, and a thermostat with what appears to be a temperature sensor.

After some searching, I couldn't locate the thermostat alone. It appears I may need to just replace the entire pump.

I do believe the thermostat is possibly to blame. I went ahead and threw it in a pot of boiling water, and saw no opening or change in its configuration. Not sure if the thermostat requires heat with some sort of positive pressure to open. After heating it, I did try and apply pressure to the valve, and wasn't able to get any movement.

It doesn't appear that there is anything wrong with the water pump itself. I applied torque to the pulley while holding the impeller tight. There was no obvious spinning or separation between the parts.

I think at this point, I have no choice but to replace the entire water pump itself. Any thoughts?

Thanks.

I see aftermarket pumps on ECS for reasonable prices. You could swap over what you need to your oem pump if you were concerned about that. Great username btw!