# Coolant Temperature Issue



## Scotsman1971 (Nov 10, 2016)

Hi All,

New to the group.

I've had my 2011 CC for a couple of months now and have a coolant temperature issue. 

It started the temperature gauge would not rise off the bottom - I could drive for over 45 minutes at approx 60 mph with no movement. Reviewing the forum and being a bit of a DIY'er I figured the thermostat was stuck open.

Change the thermostat last Saturday - complete pig of a job. Anyway, after changing the stat on taking the car for a short run the gauge started to rise up to about 85 deg.C. On getting home I checked the coolant bottle and it was low so I opened it, not thinking about it being pressurised and the level in the bottle rose above the max. Left the car to Sunday morning, topped up the coolant to the max level and took the car for a drive and again the gauge started to rise to approx 75 Deg.C (just a short run). Didn't use the car much more on Sunday but the wife drive if for about 40 mins. Monday morning went to start the car and had a low coolant warning so topped up the level. Figured this is fine as the air comes out with the stat opening and closing.

Drove to work (75 miles / 90 minutes). The gauge never reached the middle (90 Deg.C). Same on Tues, Wed & today. The gauge does rise to approx 70 Deg.C after about 15 - 20 minutes and will then move up and down by approx +/- 10 Deg.C. Oil temperature on the display varies from about 65 - 80 Deg.C. Coolant temperature is always about 10 Deg.C lower than the oil.

Here's my thinking:

Option 1:
The new thermostat is working. This is why the temperature on the gauge moves - as the stat opens and closes. The coolant temperature sensor is faulty and giving low readings. The gauge has a dead band around the mid point (90 Deg.C) so it does not move when at normal operating temperature. As the gauge never reaches the middile the 'dead band' does not function.

Fix: Change the coolant temperature sensor. Anybody know where it is located?

Option 2:
With opening the coolant bottle on Saturday evening and releasing the pressure quickly it has caused the stat to stick open again. This results on the temperature / gauge never reaching 90 Deg.C.

Fix: Fit another new stat. Hope it's not this as it is a nightmare of a job.

Other info:
Outside temperature has been between 0 and 6 Deg.C. Heater is working but I don't know if it blowing hot or only warm as I've not long had the car and not needed to use the heater till the past week.

Any idea's what it could be. All suggestions welcome.

As you may guess I'm from Scotland but I'm actually in Ireland.

Thanks All.


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## OEMplusCC (Jan 27, 2013)

Scotsman1971 said:


> Hi All,
> 
> New to the group.
> 
> ...


Personally, I would first grab a vagcom and do some basic test.

1. I would go to 01- engine module and see what temperature is being reported by ECU. I would then correlate that to what your gauge shows
2. I would then go to 17- instrument cluster module and do basic output test on the gauge just to make sure the gauge is not broken
3. Look for any error codes


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## Scotsman1971 (Nov 10, 2016)

Quick Update: This morning going to work the temp gauge took a good while to heat up and then only reached about 75 Deg.C and the oil temp was always higher was about 2 Deg.C). Then this evening the temp gauge was up to 80ish on the motorway (half an hour at 80mph) and the oil temp was around 85. Then when I get into town the gauge goes to nearly 90 (mid point) and the oil temp was still 80 - 85. First time the gauge has been higher than the oil temp.

Thanks OEM. I'll try those tomorrow before going to the motor factors to see about a Coolant Temperature sensor (CTS). 

Can't think on anything else it could be given that the cooling system is just a pump circulating water, a valve (stat) that opens/closes at a set temperature to allow the water to go in to the rad to cool it and a temperature sensor to let the ECU and the gauge know what temperature the water is at.


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## CC'ed (Dec 1, 2009)

1) Make sure all the air is bled out : follow the VW Factory Service Manual for the correct procedure.
2) The Coolant Temp Sensor is part of the water pump housing, located on the left side....should have changed that when you did the thermostat....
3) VAGCOM (or a generic scan-tool which can read engine operating temperature) reads the engine temp from this same sensor that the instrument cluster gauge uses, so the 2 values should coincide (unless the temp is above about 85C, when the gauge needle stops moving (it is in a dead-band from about 80C to about 110C).


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## Scotsman1971 (Nov 10, 2016)

Well. Went out and checked the car yesterday using VCDS.

Started the car from cold to make sure the radiator fans were not running all the time making the time to heat up longer. They were not running so ok. Left the car running while using VCDS.

In '01-Engine' I looked at the following:

066 - Coolant Temperature
067 - Coolant Temperature at Radiator Outlet; actual value
099 - Engine oil temperature

To start with 066 was indicating -40 Deg.C so that was strange.











In '17-Instruments' I looked at the following:

082 - Coolant temperature
107 - Engine oil temperature










When the temperature gauge was indicating 80ish I got the following in VCDS:
066 - Coolant Temperature = 70
067 - Coolant Temperature at Radiator Outlet; actual value = 70.0
099 - Engine oil temperature = 74.0
082 - Coolant temperature = 69.00
107 - Engine oil temperature = 74.0

When doing this the radiator fans were coming on when the gauge indicated about 80 - seemed low as would stop the temp reaching 90.

I let the car cool and then changed the Coolant temperature sensor as I already had a new one. At this point my VCDS decided to go on the blink and not work - software would not detect the cable (that's today's job to fix).

Car warmed up and took to a run. When I got back I let it tick over. The gauge did eventually get up to 90 and this time without the radiator fans kicking in. I also had the heating on high and it looks like I got more air out the system as the level in the bottle dropped - I'll check it again this morning before starting the car.

I stopped the car and as a test disconnected the CTS I'd just installed. Turned the ignition on (not started) and the temp gauge went back to 90 - so the sensor I changed is not connected to the gauge - maybe its linked to when the rad fans come on.

*Questions:*
During the first tests: 

067 - Coolant Temperature at Radiator Outlet; actual value started around 20ish and came rose as the other temperatures rose. Given that the thermostat should be closed to start with should 067 reading/temperature not lag a good bit behind the others until the stat is open and the water is circulating through the rad as well as the engine?

Does this point to the new stat I fitted may be faulty and is opening too soon/early?


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## SandmanG500 (Nov 12, 2016)

Check for CTS wiring continuity.


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## supra661 (Mar 22, 2007)

*Did you find any instructions anywhere to change that thermostat?*

Hey, I have similar issue... Thermostat always running slightly cold, throws a check engine light and when it is cooler weather outside like now in Flirida, the gauge does not reach normal running temp.

Bottom line, did you find any instructions anywhere on how to get down to that thermostat? 

From what it looks like, I would have to pull the whole intake (at which point I may as well plan to clean the intake valves too)... 

Just hoping you can point me to some instructions or a good write up somewhere to help. I need to do this same work very soon on my '09 CC 2.0T.

Thanks!


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## Scotsman1971 (Nov 10, 2016)

Supra661: 
Mine is a 2.0 TD and it is a pig of a job to change. You need to be able to get to it from the top and bottom (my mate has a pillar lift which helped). You need to remove the air inlet pipe and take out the bolts holding the alternator so you can move it out the way (you need to remove the tension off the belt as well). You don't need to remove the inlet manifold or anything like that. The hardest bit is getting the pipe clips to move (unless you have the special tool). Then getting at the 2 bolts that holds the stat in are tricky to reach.

Took the best part of four hours to change it. If you had the special tool for the pipe clips it would have been a good bit quicker.

Update on mine:
Had it in the dealer today to do there diagnostics on it (Costs €90). After them having it for over the hour they couldn't find out what was wrong (no charge though ). They said they need it in for longer so it is booked back in for Friday morning.

What I have found is that since I changed the coolant temperature sensor my mpg has gone up.

Does anybody know where the second sensor is located? The one I changed is on the left hand side of the engine on. Looks like this: http://www.micksgarage.com/ProductDetails.aspx?pid=1254564&carid=28283

I'll update on Friday with what they find as it may help others.


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## Scotsman1971 (Nov 10, 2016)

Quick update: Car in the dealer from 08:00. They phone me around 13:15 with an update that they haven't got to the bottom of it. I talk to there technician and explain again what the issue is and what I'd already done - change stat, CTS and the testing. Also said that I know there is a second sensor but didn't know where it was. Tech said it is in the block on the gearbox side. I explained that the CTS I changed wasn't connected to the temp gauge as when I disconnected the CTS the gauge was still reading. At this point the tech said he'd go and look at the other sensor.

I go and pick the car up at 15:15 and it's not ready - they still have parts off it. About 16:00 the service manager calls me and explains what they have done including checking the wiring on the CTS and the other sensor which is all OK. They have got it down to either the second sensor or the clocks are faulty at which point I thought no **** batman it's hardly likely to be anything else.

Explain to them it can't be the clocks as when I used VCDS I could make the clock do 0, 50 & 100% and it worked fine. Asked when they can change the sensor but it is not in stock and they didn't know how much it will be.

Plan to try another dealer tomorrow morning and see if they have it in stock and I'll change it myself over the weekend. Failing that it will be back in the original dealer some time next week.

I'll update once the sensor is changed.


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## Scotsman1971 (Nov 10, 2016)

Well. I've now changed the second Coolant Temperature Sensor (it is fitted into a plastic housing on the gear side of the engine) on Saturday morning. Started the car and let it tick over. The gauge was slow to rise but did get up to 90 Deg.C. Took car out for a short run and had the heater on (it was about 4 Deg'C outside). GAuge moved slightly but stayed around the 90. Happy days it's fixed I thought.

Then today I was out in the car. It was 2 Deg.C outside. I had driven for approx 30 minutes at around 55 MPH and the gauge never reached 90. It would 70ish again then drop back down. I was out again this evening and the same thing.

It seems that if the car is parked and ticking over it will reach 90 (also driving around town the temperature rises). When driving out of town the temperature doesn't rise.


Here's my current thinking:

CTS - Both replaced with new so not the issue.
CTS wiring - checked by VW dealer and OK. Also, if the wiring was faulty the gauge would either work or not as it is a variable signal.
Error codes - VW dealer checked this and there we none.
Thermostat - replaced already but it may be stuck open with me releasing the pressure too quick when the coolant was hot - replace stat again??

Any other ideas out there as I'm running out of them.


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## CC'ed (Dec 1, 2009)

I think your instrument cluster ("clocks" as you say) is bad. Doing the VCDS coolant gauge indicator test may not really test all the circuits in the cluster that are associated with the coolant gauge, I suspect that the analog "front-end" circuit, which is between the coolant temp sensor and the microprocessor of the instrument cluster, is defective/intermittent. The VCDS gauge test probably only tests the micro and the actual gauge meter movement, not the analog front-end circuit.


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## Scotsman1971 (Nov 10, 2016)

Update on the on-going coolant temperature saga.

I had the car into an independent VW garage on Monday. They thought it was due to me not using a genuine VW thermostat so the fitted a new one - no difference.

More digging about on youtube and the net and I found out that cars with a DSG gearbox have a second thermostat - an in line one.

Link to youtube where I initially found out about the in-line stat: https://www.youtube.com/watch?v=z7R8UFvJzos

Link MK5GTI forum which has more info on them: http://www.mk5golfgti.co.uk/forum/index.php/topic,78341.msg817626.html#msg817626

Link to another web page that has info on them (not in english so need to translate it with google chrome): http://www.maximilian-sell.de/passat-b7-dsg-thermostat/

Link to another page about them: http://translate.google.co.uk/trans...10&client=safari&sa=N&rls=en&biw=1572&bih=883

Bought an inline stat at the motor factors yesterday for €27. Fitted it this evening in less than an hour - you need to take the airbox off and it is then located in the coolant line going to the DSG gearbox. Biggest pain is putting the pipe clips back on.

Took the car for a run and within 5 minutes the temperature was past 80 Deg.C and a few minutes later was up to 90 so fixed at last.

Part number for the inline stat is: 4E0 121 113

So if you have a problem with you car not heating up and you have a DSG gearbox I'd recommend that you look into changing the inline stat. It's cheaper and easier to replace than the main stat.

Hope this helps others with similar issues.


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## kbad (May 26, 2007)

oi mate .. welcome to the vortex and congrats on your cc .. good call on the inline dsg thermostat, glad you got it sorted out .. "In order for your transmission fluid to warm itself to operating temperature under extreme cold conditions this thermostat may remain closed until coolant reaches a certain temperature. This thermostat is located in the main line leading to the transmission oil cooler assembly." ... enjoy the ride .. good luck!


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## OEMplusCC (Jan 27, 2013)

Scotsman1971

Kudos for posting back with your solution.... :beer: I'm sure it will help out someone in the future.


I hate when you have people who just create an account to ask question and leave


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## CC'ed (Dec 1, 2009)

I don't think USA CC's with the 2.0T gasoline engine have this 2nd DSG coolant line thermostat.


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## Saff172 (Feb 25, 2021)

Hi guys, i have changed my thermostat and my coolant temp sensor. However still no luck! My temperature gets to 90 and then drops on a motorway run then when driving back on local roads it goes slightly back up close to 90 and then drops if i put my heaters on. 

My car is a 2012 audi a3 2.0tdi 140 black edition dsg. Is there some kind of inline thermostat that i need to change... i did replace a whole coolant hose pipe which came with the inline thermostat at the end. However this was a used part from the scrap yard... obviously still not sticking to 90 where it should be...


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