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Discussion Starter #1
I have done my best to search clubtouareg, vwvortex, and google and have come up short on finding much on the newer models with regard to overheating. Created an account to post this question. Thanks for any help you can offer.

Model:
2012 Touareg Lux V6 3.6L 80k miles

Issue Description:

The Treg will sometimes overheat about 10 mins after cold start. Temp gauge goes into the red (260F +) with a warning on the dash to check coolant level. When this happens, pull to the side of the road and it cools off quickly (like 2-3 mins). After it cools back to the nominal 200F on the dash, it doesn't overheat for the rest of the trip.

I have VCDS and pulled one code: P2181 performance malfunction in cooling system and the freeze frame data shows a coolant temp of 72C (normal). I just replaced the thermostat three days ago. The old one was broken and I thought I had the problem licked. It drove fine for 2 days but them the issue returned on the next two days. When it overheats, I turn the inside heater on HI and noticed that for a brief moment that cool air came out but then was hot again (happened twice). This leads me to believe I have air in the system. The coolant level is fine. I have been watching it to see if it falls much (meaning air was escaping) but I haven't seen an appreciable difference.

Service History:
- 40k miles, carfax indicates that the thermostat and water pump was replaced
- 43k miles, carfax indicates that the termostat and water pump was replaced again as well as the thermostat housing and coolant temperature sensor.
- 80k miles I replaced thermostat and drained coolant, replaced with G13 coolant

Possible issues:
- Thermostat: Symptoms still sound like a sticking thermostat. Could have gotten a bad thermostat.
- Air in the system: The fact that cool air came out a little bit with interior heater on really sounds like air in the system but the system should be self bleed. Maybe I have a plugged return line or something. I plan to remove the little line on the top of the expansion tank to ensure a stream of coolant is coming through when the system is at temperature
- Sensor: Seems like the older touaregs have 2 sensors. I can only find 1 sensor on the parts diagrams but VCDS does offer 2 readings (can someone confirm if mine has 2 sensors? I see the one at the rear driver's side of the engine) . Maybe the sensor is bad but the system isn't even overheating. The dash does not appear to act like a bad sensor... the needle moves smoothly and doesn't jump around.
- Electric Fan: Nope, I have confirmed the fan is off when cold and on when hot.
- Head gasket: Please no... I am close to spending $40 to get the exhaust gas leak tester thing just to cross this off.

Thoughts?? Thanks in advance.
 

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My V8 (I know, different motor) needed a little time until the air got purged after a complete drain and refill of the cooling system. It took 1 or 2 drive cycles, IIRC, to "self purge".

Now, most newer cars require an air purge of the cooling system any time it's opened up.
:- /
 

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Discussion Starter #3
Thanks for the reply. We have driven it 4 days totaling 7 drive cycles. The first 4 were fine and the last three had an overheat. I think you are right that it is an air bubble. I just ordered the vacuum fill kit from ECS tuning. Hoping I don't have to drain the system first.. there is no good way of draining and catching the coolant. Opening the lower radiator hose only empties the radiator unless the system is hot enough for the thermostat to be open. Cheers.
 

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Interesting. The history seems to indicate this may be an old problem that hasn't been solved, but that isn't original to the vehicle (think engine casting defect) and stemmed from some unknown event. Was the thermostat OEM or some aftermarket job (only buy OEM).

Was the secondary pump (the electric one) one of the items that didn't make it to the T3? Might check this (if you have it).

Seems clearance related...like something is making the thermostat stick part of the time. Have you done a proper pressure coolant flush? Not just a drain and fill. Someone could have put some leak fix crap in your system at some point and it could have gummed stuff up??

Whatever it is is sure odd.

Another strange solution...(doesn't fit your issues...just is interesting) is someone had a radiator where the vanes were packed full of mud from offroading. A careful wash fixed his (again not your issue).
 

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Discussion Starter #7
Thanks all for the replies. We have had about 14 successful drive cycles now without any overheat. Meanwhile, the cooling system vacuum tool came... I did not pull a vacuum on the system nor did I re-drain the system and do a proper flush. I will if it overheats again. Here are some shots at the questions I missed.

- The old thermostat was definitely broken and came out in three pieces. The plastic was white.. I didn't check to see if it was OE. The replacement thermostat I bought was from RockAuto and was not OE. It was easy enough to replace if it does fail (as long as I don't warp a head if it does go).
- The overheat after the thermostat replacement was most likely a bubble in the system. I did not have the vacuum tool when I refilled the system so it was not filled correctly. I think the bubble was somewhere in the heater core since cool air came out of the system briefly when the system was at temperature (yes I turned the heat and fan on to ensure heater core valve was open before filling the system). The system must have successfully self bled the air bubble out over three days.
- I don't have more details on the past issues so I can't tell if there is a systemic issue or not. I am definitely worried about this but I think time will tell. There was 40k miles between the previous issues and now. I hope I just got a flawed thermostat.
- The old coolant was very clean and clear. I don't think there was any leak stop stuff added but I can't tell for sure.
- I didn't see how the aux coolant pump could cause this issue. It is used to ensure a hot engine does not overheat after the engine is turned off since no coolant or air is moving. Unless the aux afterrun pump is required to assist the system to bleed... I never heard that pump kick on after I shut off the engine.
- Radiator fins are fine. It cools with no issues after the initial overheat. I ran it hard to try and intentionally overheat it and could not so I ruled out radiator and water pump.


My big lesson learned is that I should really do the correct coolant fill procedure if the cooling system is opened. Thanks all.

Siiboga.. I'll post some thoughts on your thread.
 

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2012 touareg has a 10 year 100,000 mile powertrain warranty, unless you like pulling your hair out trying to diagnose and flushing money away bring it to a dealership.

Sent from my SM-G930T using Tapatalk
 

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Had this issue on my '12 TDI Exec. Off we went on vacation only to get 50 miles away and my temp gauge starts going HOT.
1st the dealership thought it was a Thermostat sensor... they replaced. Week later starts again......this time its coolant pump.
They replaced (thank you Wrap warranty..lol)

Been good to go since!!!
 

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Discussion Starter #10
The stupid thing overheated again this morning with cold air coming from the vents when it was too hot. Guess I'll get to use that coolant system refill tool after all...
 

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Discussion Starter #11
Well I drained the coolant and used the vacuum tool to put the coolant back in and it still overheated. I took logs of the engine coolant temperature and oil temp. It looks like as soon as the coolant reaches 189 F (temp that the thermostat is supposed to open) the temperature immediately starts climbing quickly. I talked to a dealer tech and they said to always use OEM parts and that the water pump has some sort of shroud that helps the engine reach operating temperature quickly. There is a N545 valve that operates the shroud and it sounds like that might be the problem. I looked at parts diagrams and I cannot see any reference to this shroud or valve. It is possible that it is internal to the pump.

Also, I am able to log 2 Engine Coolant Termpatures with VCDS (ECT1/ECT2) but I cannot find a second coolant temperature sensor on this engine. I see the one at the rear of the engine on the driver's side but there is none on the radiator.

1) Can anyone validate the water pump shroud or N545 valve thing is real?
2) Can anyone confirm how may coolant temp sensors the T3 3.6L has and where the second one is?
 

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As a general rule on VW, always OEM. Less frustration is always worth its weight in gold. Been there done that with many parts over the years.

The other sensor is on the radiator (per page 40 of the pdf I attached in previous post.)

The last aftermarket part I ever used was a starter in a 1988 16V. Install was a PITA, during last bolt tightening the protective shroud cracked exposing internals!!!! I never purchased an aftermarket part after this (exception being the Touareg center main bearing because that OE design is rubbish).
 

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Discussion Starter #13
I looked at the PDF you attached (thank you) and see the 3 temp sensors listed but I do not see Coolant Temp Sensor G85 on my TReg and cannot find it in the parts diagrams at VW Parts website. I am thinking the T3 3.6L does not have a 2nd coolant temp sensor on the radiator.

Entire Cooling System (the one coolant temp sensor is not labeled but near #5:
https://parts.vw.com/a/Volkswagen_2012_Touareg36LV6-Lux/_53892_6001587/MAIN-HOSES--LINES-COOLING/9241077.html

Waterpump (same temp sensor #15):
https://parts.vw.com/a/Volkswagen_2012_Touareg36LV6-Lux/_53892_6001426/MAIN-WATER-PUMP-COOLING/9241088.html

Radiator (no temp sensor):
https://parts.vw.com/a/Volkswagen_2012_Touareg36LV6-Lux/_53892_5981255/RADIATOR--COMPONENTS-COOLING/9241075.html

Waterpump and Radiator (no temp sensor):
https://parts.vw.com/a/Volkswagen_2012_Touareg36LV6-Lux/_53892_6387263/COOLING-SYSTEM-RADIATOR-WATER-PUMP/F50C040.html
 

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Seems missing. You might just call dealer parts guy...really common motor.

In the last link: It goes in #3 left (smaller component...lower radiator hose). You can even see the spot for it. Here is an actual picture of the joint between these two number three items (sorry for how filthy my engine is, my truck was built eleven years ago and has been offroading a bit and in snow often as well). The left one has the sensor in it.

Standing at front of truck, passenger's side, look down and it is directly in view (on mine unless something changed).

It is possibly this was done away with in later engine generations...but just seems unlikely.
 

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Seems missing. You might just call dealer parts guy...really common motor.

In the last link: It goes in #3 left (smaller component...lower radiator hose). You can even see the spot for it. Here is an actual picture of the joint between these two number three items (sorry for how filthy my engine is, my truck was built eleven years ago and has been offroading a bit and in snow often as well). The left one has the sensor in it.

Standing at front of truck, passenger's side, look down and it is directly in view (on mine unless something changed).

It is possibly this was done away with in later engine generations...but just seems unlikely.
Thanks for all your input. I have pulled the lower radiator hose twice and can guarantee that there is no sensor on the lower hose connection. I am not sure if the 2nd sensor has been deleted but at minimum it has been moved.
 

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There is a flow check valve in the coolant hose right off the cylinder head (above the cooling fans), it uses a plastic ball, sometimes the ball gets hammered into the plastic hole, remove and inspect.

Check vacuum supply to your water pump, the diaphragm should indefinitely hold a vacuum, also watch vacuum supply from the supply solenoid it should open producing a vacuum on cold start and then after a few minuets of run time turn off opening the shroud for coolant to flow.
 

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2012 touareg has a 10 year 100,000 mile powertrain warranty, unless you like pulling your hair out trying to diagnose and flushing money away bring it to a dealership.
This is 100% true unless your vehicle was totaled at some point,

OP Bring your car to the dealership, powertrain coverage is FREE
 

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Discussion Starter #20
Thank you very much for the vacuum tip. I still can't find the part on a diagram but should have enough to test with.

Yea.. I hate dealers. The nearest one is 45 mins away and I still hold a grudge about an alignment lie they told me on my past B5S4 (yes you can freaking adjust camber but it sucks to do it by moving the entire subframe). I have never owned a car new enough to have warranty and always wrench on my stuff. We bought this used also so I assume the warranty transfers. Bottom line is that I am stupid and haven't tried to figure out the warranty stuff. If I can't figure it out this weekend, I will go the warranty route.

Thanks for all the help.
 
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