# TT thinks it's overheating---but it's not. Cluster repaired, greentop sensor swapped.



## CageyBee (Jun 15, 2000)

*FIXED: solution below*

Hi all, my '03 TT roadster seems to think it's overheating. The gauge goes into the red, the overheat icon starts flashing-and the kicker the rad fans go on high.

I've searched the forums and the internets and can't seem to come to anything conclusive. Here are the steps I've taken:

1) Had the cluster repaired -> no effect
2) replaced the green temp sensor -> no effect
3a) hooked up a "scangauge" to the OBD2 port -> coolant reads accurately (72*C)
3b) the climate control shows a bad value for #49, it shows -10*C. 
3c) #51 shows about 20 degrees less than my OBD2 reader.

What I don't understand is how the rad fan turns on, what triggers that? I thought it was triggered by a rad fan switch, but clearly something else is at play. The second the cars beeps at overheating (and flashes the icon) the rad fan comes on. Can somebody tell me what sensor sends the value for #49?

Any advice is greatly appreciated, I'm lost!

Thanks

-danny


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## TTC2k5 (May 23, 2008)

Waterpump issues??


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## CageyBee (Jun 15, 2000)

TTC2k5 said:


> Waterpump issues??


Nope, I just the waterpump+belt+tensioner last year. I also replaced the electric waterpump earlier this year.

To confirm, I'm 100% certain the car isn't overheating. It's been doing this for month and there has never been any true indicators of overheating.

Also, an extra tidbit for those curious is that 49C reads what I believe to be accurate when it's not misbehaving. The problem is somewhat intermittent but will occur every time I drive the car. It's like it gets a bogus reading 50% of the time. Is it normal for 49C to display such an oddball reading (-10*C) when you first start it up (in the middle of summer)? 

THANKS

-danny


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## omarquez510 (Apr 5, 2009)

How long did you let the car idle before running your scantool? 

Also, what kind of driving causes the gauge to rise? If it's intermittent i would check electrical connections. Make sure your ECT sensor is plugged in correctly.I'll TRY to get you a wiring diagram when i get back to my apartment.

Read page 4:
http://www.autoshop101.com/forms/h32.pdf


BTW average Engine coolant temp sensor should see 200-250 degrees f


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## fetah (Sep 10, 2006)

I had the same thing happening on my car and I replaced teh cluster. Didn't repair it. Fixed the problem.


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## CageyBee (Jun 15, 2000)

omarquez510 said:


> How long did you let the car idle before running your scantool?
> 
> Also, what kind of driving causes the gauge to rise? If it's intermittent i would check electrical connections. Make sure your ECT sensor is plugged in correctly.I'll TRY to get you a wiring diagram when i get back to my apartment.
> 
> ...


Thanks for the think-but I must apologize I'm not quite sure what I should be looking for.

Sometimes the car will report overheating immediately after starting up the car. It is not dependent on driving. When you say ECT sensor, you mean next to the battery? I just replaced that this morning with a new sensor-no result unfortunately. 

Is there more than one temp sensor? Does anybody know where 49C and 51C pull their data from?

I suspect it is the cluster that is bad but I really want make sure that's my last resort as the fix is over $1400 as the dealer does not want to supply me a new cluster (bah!)

Thanks again

-danny


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## Late__Apex (Dec 2, 2007)

The beeping and flashing temp icon can also be caused by indicated low coolant levels. This can be because of 1) actual low coolant levels or 2) a corroded or bad coolant level probe or bad connection at the plug. The probe is in the overflow tank. Check your coolant level and if it is good check the probe.


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## CageyBee (Jun 15, 2000)

Late__Apex said:


> The beeping and flashing temp icon can also be caused by indicated low coolant levels. This can be because of 1) actual low coolant levels or 2) a corroded or bad coolant level probe or bad connection at the plug. The probe is in the overflow tank. Check your coolant level and if it is good check the probe.


Thanks!!! The coolant level is accurate and I'm certain of it---the icon beeps and flashes when the needle is pegged fully to the right (indicating overheating).

Incidentally, I do know that the coolant level sensor is working accurately as I did run low on coolant a few months ago when my electric waterpump sprang a leak and spilled my coolant everywhere overnight.

With that being said---is there only one coolant sensor in the entire car? And how does 49C and 51C get their data?

Thanks again

-danny


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## CageyBee (Jun 15, 2000)

so-nobody knows where 49C gets its data from? Pretty please :beer::beer::beer:


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## bauch1425 (Jun 29, 2006)

It's all from the same green top sensor. IIRC, the coolant sensor is dual sided. One side sends the data to the instrument cluster (49C) and the other side to the ECU (rounded value, 51C). I've had my 49C readings start falling 1 deg C at a time until it reaches -10 deg C (which I assume is the absolute minimum for the sensor). 

I've had around 4 fail on me - weird how the black top sensor lasted WAY longer, yet they're the bad ones...


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## DurTTy (Aug 14, 2007)

check your thermostat --- thast what triggers the fans on. 

basically, what may be happening is that your T-stat may not be engaging until the car starts to overheat and then triggers the fans. 

when you did the tbelt job-- did you get an oem tstat or aftermarket ? 

basic check instructions. 

1.) let the car do what you describe at the top. 
2.) pop the hood. 
3.) grab the lower rad hose ( dont burn yourself lol) this is the rad to t-stat hose 
4.) grab the top rad hose, this is the engine to rad hose 

!! IF !! the lower rad hose is *considerably* cooler than the top rad hose then the t-stat aint working properly 

IF they are pretty much the same temp then there is proper flow of coolant to and from the motor and you need to look elsewhere. 

give it a shot. :thumbup: 

IIRC the car takes 2 Water temp readings 1 at the WTS and 1 at the Tstat.


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## bauch1425 (Jun 29, 2006)

What? The thermostat is completely mechanical. There is no electrical sensor there.


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## DurTTy (Aug 14, 2007)

check the bentley, if the 2nd coolant reading isnt at t-stat housing assembly then its somewhere along the rad hosees. 


in either case, the OP is showing signs of a malfunctioning T-stat and should get it checked out b4 he blows the headgasket.


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## CageyBee (Jun 15, 2000)

bauch1425 said:


> It's all from the same green top sensor. IIRC, the coolant sensor is dual sided. One side sends the data to the instrument cluster (49C) and the other side to the ECU (rounded value, 51C). I've had my 49C readings start falling 1 deg C at a time until it reaches -10 deg C (which I assume is the absolute minimum for the sensor).
> 
> I've had around 4 fail on me - weird how the black top sensor lasted WAY longer, yet they're the bad ones...


I agree with -10*C being the lowest of the range---I just replaced that green top sensor so i thought that would have fixed that-but I get the same results as my old green top.

I'm wondering if 49C piggybacks off the cluster-and it's actually the cluster that's reporting the bad (bogus) temperature.

I don't think the car is overheating. It just thinks it is. The rad fans coming on is a mystery to me because they can come on right when I start the car even after it's been sitting for a whole day. I thought the fan was controlled by the rad fan switch. 

I'll have to triple check that it isn't really overheating... Thanks for all the help-this one is truly a mystery to me.

-danny


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## CageyBee (Jun 15, 2000)

DurTTy said:


> check your thermostat --- thast what triggers the fans on.
> 
> basically, what may be happening is that your T-stat may not be engaging until the car starts to overheat and then triggers the fans.
> 
> ...


Well tell you what-the lower rad hose does feel considerably cooler---much, much cooler. The rad feels hot and the flow of radiator fan air blows very hot, so I suspect the tstat is working...yet the lower hose feels warm but not hot. Isn't it possible that the rad is just cooling the coolant that well? 

I'll replace the thermostat if the general consensus here is that it's a good idea.... 

Still doesn't tell me why 49C still shows -10*C though 

Thanks again and as always i'm always open to any ideas or thoughts.

-danny


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## DurTTy (Aug 14, 2007)

CageyBee said:


> Well tell you what-the lower rad hose does feel considerably cooler---much, much cooler. The rad feels hot and the flow of radiator fan air blows very hot, so I suspect the tstat is working...yet the lower hose feels warm but not hot. Isn't it possible that the rad is just cooling the coolant that well?
> 
> I'll replace the thermostat if the general consensus here is that it's a good idea....
> 
> ...


there should not be a HUGE difference between the coolant hoses. the system is designed to maintain a relatively constant temperature.

if you have an OEM T-stat it should be aprx 87* C to 90*C -- anywhere north of that should start to trigger the fans by opening the t-stat. 

if you blast the heating to max-- will the temp slowly go down? does it blow as hot air as you expect Max to? have you done a coolant system flush at any point? 


get a vag-com or go to a vw shop with a vag-com and have the car scanned to see what the CTS reading is vs the cluster readout, 

while your there, have them do a cluster readiness check and check for Trouble Codes.

the $30 you may pay for the scan may end up saving you $$ 

try this before you go an buy a T-stat to replace. --- tstat apprx $30 with gasket, labour apprx 30 -45 minutes..


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## CageyBee (Jun 15, 2000)

DurTTy said:


> there should not be a HUGE difference between the coolant hoses. the system is designed to maintain a relatively constant temperature.
> 
> if you have an OEM T-stat it should be aprx 87* C to 90*C -- anywhere north of that should start to trigger the fans by opening the t-stat.
> 
> ...


Thanks for the heads up. There is def. a big difference in coolant hoses but I'm fairly certain there is flow through the hoses---I can feel water trickling through the bottom pipe via the electric waterpump. I had the waterpump/timing belt changed last year (ESS) and thought the thermostat was done too but I could be wrong. I don't mind swapping the tstat and it's something that i'm more than able to do anyway. I do have a VAG COM cable... here's what came out:

VAG-COM
Windows Based VAG/VAS Emulator
Version: Release 311.2-N
www.Ross-Tech.com
Dealer/Shop Name: auditt
Workshop Code: 000 00000
Self-Diagnosis Log
Friday, 13 August 2010, 22:36:54
VIN Number: TRUTC28N431003116 License Plate:
Mileage: Repair Order:
Chassis Type: 8N - Audi TT
Scan: 01,02,03,08,15,17,22,35,37,45,54,55,56
Address 01 -------------------------------------------------------
Controller: 8N0 906 018 BD
Component: 1.8L R4/5VT G 0002
Coding: 07570
Shop #: WSC 01236
TRUTC28N431003116 AUZ5Z0B8066084
1 Fault Found:
18058 - Powertrain Data Bus: Missing Message from Instrument Cluster
P1650 - 35-10 - - - Intermittent
Readiness: 0000 0001
Address 02 -------------------------------------------------------
Controller: 09G 927 750 L
Component: AQ 250 6F 0301
Coding: 0008201
Shop #: WSC 01236
No fault code found.
Address 03 -------------------------------------------------------
Controller: 8N0 907 379 J
Component: ESP FRONT MK60 0101
Coding: 0019473
Shop #: WSC 01236
No fault code found.
Address 08 -------------------------------------------------------
Controller: 8N0 820 043 A
Component: TT-KLIMAVOLLAUTOMAT D03
Coding: 00140
Shop #: WSC 01236
No fault code found.
Skipping Address 15-Airbags
VAG-COM
Self-Diagnosis Log
Friday, 13 August 2010, 22:36:54
Page 2
VIN Number: TRUTC28N431003116 License Plate:
Address 17 -------------------------------------------------------
Controller: 8N1 920 930 S
Component: KOMBI+WEGFAHRS. M73 D04
Coding: 06344
Shop #: WSC 00000
TRUTC28N431003116 AUZ5Z0B8066084
2 Faults Found:
01039 - Coolant Temperature Sensor (G2)
29-10 - Short to Ground - Intermittent
00668 - Supply Voltage Terminal 30
53-10 - Supply Voltage Too Low - Intermittent
Address 35 -------------------------------------------------------
Controller: 8N7 962 267 F
Component: Central Lock/Alarm D08
Coding: 15900
Shop #: WSC 93030
1 Fault Found:
01371 - Alarm triggered by Door Contact Switch: Driver's Side
35-00 - -
Address 55 -------------------------------------------------------
Controller: 4B0 907 357
Component: LEUCHTWEITEREGLER D004
Coding: 00010
Shop #: WSC 01236
No fault code found.
Address 56 -------------------------------------------------------
Controller: 4B0 035 186 H
Component: concert II NP2 0007
Coding: 00202
Shop #: WSC 93201
2 Faults Found:
01317 - Control Module in Instrument Cluster (J285)
49-10 - No Communications - Intermittent
01336 - Data Bus for Comfort System
49-10 - No Communications - Intermittent
End -------------------------------------------------------


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## DurTTy (Aug 14, 2007)

sounds like the cts is bad or the clip may be bad (terminals)

take the connector off, and inspect it for any damage, corrosion, loseness, is the metal clip that holds it in place rigged correctly? 

check the bentley for operating ranges and with a volt meter check the readings. compare and follow the instructions or have a mechanic diagnose the issue said. 

i suggest you clear the codes, drive around and when it throws a hissy fit, read the codes again. if the same ones appear .. check the CTS again. 

short to grown//insufficient voltage will definitely give you some weird readings.


also ... doesnt look like you used the vag-com to read out what the CTS temp says and compare to cluster readout and the Heating display. i suggest you take that step at least


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## CageyBee (Jun 15, 2000)

DurTTy said:


> sounds like the cts is bad or the clip may be bad (terminals)
> 
> take the connector off, and inspect it for any damage, corrosion, loseness, is the metal clip that holds it in place rigged correctly?
> 
> ...


First, let me start by thanking you for all your help----it's been HUGE! Really, I owe you a beer or two.

I've made some progress... turns out the thermostat was bad after all. That means that the overheating signs were probably true. After replacing the thermostat the lower rad hose is now as hot as the upper rad hose. I don't even know how long the car has been overheating for. The thermostat replacement wasn't tough but I did manage to break the dipstick in the process. For now I've corked the hole with a cork but will replace it this week.

It appears as though the cluster now shows the true temperature, but only after some time. 49C was showing -10*C until it finally started creeping up 1 degree at a time to show the true temperature (after about 5 minutes after the t-stat opened).

I suspect there is some bad wiring or a bad ground-as you suggested. I disassembled the sensor and inspected the plug and wiring for any damage but it really does look good as new. 

re:


> also ... doesnt look like you used the vag-com to read out what the CTS temp says and compare to cluster readout and the Heating display. i suggest you take that step at least


I don't know how to extract that reading, although i did try. Any chance you can point me in that direction?

All in all I feel pretty good about my progress, I think the problem here was the tstat wasn't opening, in addition to the green top sensor not outputting the true value. Hopefully I'll get the bottom of this soon.

Thanks again,

-danny


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## Late__Apex (Dec 2, 2007)

CageyBee said:


> I don't know how to extract that reading, although i did try. Any chance you can point me in that direction?


Many of the engine measuring blocks include coolant temperature including 001, 004, 011. See here for info on measuring blocks.


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## DurTTy (Aug 14, 2007)

CageyBee said:


> First, let me start by thanking you for all your help----it's been HUGE! Really, I owe you a beer or two.
> 
> I've made some progress... turns out the thermostat was bad after all. That means that the overheating signs were probably true. After replacing the thermostat the lower rad hose is now as hot as the upper rad hose. I don't even know how long the car has been overheating for. The thermostat replacement wasn't tough but I did manage to break the dipstick in the process. For now I've corked the hole with a cork but will replace it this week.
> 
> ...


glad to see things progressing :thumbup:

if the coolant got hot enough, the cts may not operate as intended, hence the weird readings.

---- clear the codes, drive it around, check for codes again after a few on/off cycles.


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## ECS Tuning - Audi (Oct 12, 2009)

DurTTy said:


> glad to see things progressing :thumbup:
> 
> if the coolant got hot enough, the cts may not operate as intended, hence the weird readings.
> 
> ---- clear the codes, drive it around, check for codes again after a few on/off cycles.


Good read through. While I agree the cts may have been damaged - as we all know that they fail by looking at them funny - one other suggestion I have is trying some dielectric grease on the contact points to assure electric connectivity promotion. It should combat corrosion and possible water infiltration. Worth a shot before replacing a cts.


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## Levi (Nov 7, 2001)

*hello dude from europe*

check wireing between the cts and the ecu if you havent fixed your problem you probably have a wire grounding somewhere , all the best levi ... im comming back home soon if you havent fixed your problem ill have a look


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## CageyBee (Jun 15, 2000)

Levi said:


> check wireing between the cts and the ecu if you havent fixed your problem you probably have a wire grounding somewhere , all the best levi ... im comming back home soon if you havent fixed your problem ill have a look


Wow great to hear from you Levi! Hope you're doing well man, it'll be awesome to see you around again!

Sadly I have to say my problem is still lurking. On the positive side I've learned quite a bit from this mess.

If things weren't strange enough as it is, I can report this new data.

With my coolant sensor plugged in, my fans turn to high speed, and the cluster (and 49C) report 130*C. VAGCOM will however report the true temperature at that sensor, 70*C. If I unplug the sensor, VAGCOM will report -48*C, telling me that the sensor reading is true and accurate. In addition to VAGCOM reporting a null value, the fans will turn off, and the cluster will read the true temperature value (70*C) and the 49C trick will confirm this.

So, if I lost you, if the sensor is plugged in, then the fans go to high speed and the cluster reports inaccurate temps. If the sensor is unplugged, then the cluster reports correctly and the fans run as normal. It's almost like plugging in that sensor screws with the cluster's reading. 

I traced the wiring back for quite a bit until it reaches the largest part of the bunch near the intake manifold. It all looked good but some wires did look a little pinched, but not nearly enough to affect anything.

Is there a secondary coolant temp sensor somewhere? I guess it's interesting to know what can trigger the high speed fan to turn on. I thought it was only the rad fan switch and the AC but apparently something else can as well.

As always any help is welcome! Thanks fellas, I may cross post this in one of those UK TT forums-open to advice as to which one is most effective. Alternately I can take this to a dealer but I'm terrified they'll just tell me to put in a new cluster for $1500... 

-danny


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## CageyBee (Jun 15, 2000)

if anybody has any idea's I'm more than happy to hear them out


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## ManualOrNothing101 (Mar 2, 2009)

When this happened to me, the problem was that one of the fuses melted in that little fuse box with all the big guage wires connected and **** next to the battery and ****ed up the whole electrical system. Did you check those ?


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## CageyBee (Jun 15, 2000)

SupraSkylineSTI said:


> When this happened to me, the problem was that one of the fuses melted in that little fuse box with all the big guage wires connected and **** next to the battery and ****ed up the whole electrical system. Did you check those ?


Thanks for responding. Yes, I did check that fusebox and all the fuses were good. 

When this happened to you, exactly what were the symptoms?

Thanks! Danny


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## ManualOrNothing101 (Mar 2, 2009)

I'd just be driving along and the temp needle would randomly soar to max. So I'd pull over, and the car was basically making itself overheat for no reason somehow. I replaced the thermostat myself, and in the process I discovered that one of the fuses in the seperated fuse box with the big wires connected to it was absolutely melted and destroyed. I replaced it and voila, never had any more problems like it again.


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## MyTToy (Oct 19, 2006)

SupraSkylineSTI said:


> When this happened to me, the problem was that one of the fuses melted in that little fuse box with all the big guage wires connected and **** next to the battery and ****ed up the whole electrical system. Did you check those ?


If you haven't checked this, it may be your problem... it is VERY common. Just open the little fuse box on top of your battery. If you see any kind of melting or corrosion, it needs to be changed, along with the wires. Is your HVAC also blowing warm from time-to-time? That's also a sign.


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## CageyBee (Jun 15, 2000)

SupraSkylineSTI said:


> When this happened to me, the problem was that one of the fuses melted in that little fuse box with all the big guage wires connected and **** next to the battery and ****ed up the whole electrical system. Did you check those ?





MyTToy said:


> If you haven't checked this, it may be your problem... it is VERY common. Just open the little fuse box on top of your battery. If you see any kind of melting or corrosion, it needs to be changed, along with the wires. Is your HVAC also blowing warm from time-to-time? That's also a sign.


Absolutely not, the fuses are all in tip top shape and so is the wiring. There is a little mystery connection behind the battery sandwiched between the airbox and the battery. Any ideas what's stored in there?


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## CageyBee (Jun 15, 2000)

Finally fixed the problem. The connection at the back of the cluster was bad. The ground was intermittent.

Other symptoms (now that it's fixed, I realized some other indicators
Fuel gauge and Temp gauge lighting was off. Sometimes they would flicker. Once the ground was fixed, this problem went away.

Also, the bad ground to the cluster caused the high speed fans to come on during startup. Contrary to this thread, the coolant fans *can be turned on by the cluster*, whether its by design or defect. It is in fact a possibility.

Thanks all for your help.

BTW sister thread here:
http://forums.vwvortex.com/showthread.php?5209136-03-TT-What-triggers-the-high-speed-fan&p=72870976

-danny


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## thomasee (Dec 20, 2012)

How did you repair the ground? i try mine from the instrument cluster ground(pin 7) to the ground under the dashboard there is no con.




CageyBee said:


> Finally fixed the problem. The connection at the back of the cluster was bad. The ground was intermittent.
> 
> Other symptoms (now that it's fixed, I realized some other indicators
> Fuel gauge and Temp gauge lighting was off. Sometimes they would flicker. Once the ground was fixed, this problem went away.
> ...


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## thomasee (Dec 20, 2012)

when my insturment clusted is connected, i move the cable harness the gauge will go to cold( engine cold). i cut open the rubber protection, the wire look good.



CageyBee said:


> Finally fixed the problem. The connection at the back of the cluster was bad. The ground was intermittent.
> 
> Other symptoms (now that it's fixed, I realized some other indicators
> Fuel gauge and Temp gauge lighting was off. Sometimes they would flicker. Once the ground was fixed, this problem went away.
> ...


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## TTquattroTT (Jul 26, 2002)

OK CaseyBee... I'm currently living your hell right now. But my life is worst. My A/C kicks OFF when the gauge kicks to decon-8 and I live in Los Angeles @ 90 degree weather.

I'm going to go home tonight and try to see if I can find the ground. Do you have any idea which connector was bad for you? Thank you.


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## etischer (Aug 28, 2010)

I spent the better part of a day diagnosing the same issue on my dash pod, so I documented what fixed mine here: 




Problems I was having include temperature gauge intermittently jumping to hot, cooling fans running high speed with engine cold, banging on dash would bring everything back to normal occasionally.


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## ozenithordie65 (May 13, 2014)

*thermostat installed correctly???????*

The Thermostat being mechanical in nature depends on heat expansion inorder to function at the appropriate temp range. If your 1.8 is like mine then the therm has a big o-ring that is supposed to sit on top of the term. if you put the O-ring between the motor and the them, then your therm is not getting as hot as your engine. in other words. metal to metal heat exchange is much faster than liquid to metal(convection heat exchange). so yeah make sure your thermostat is making contact with the block and that your o ring is not in the way. i had this issue with my Jetta, also a 1.8 turbo


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