Temp Gauge stays by the "C" when driving in the cold.

[elopez_1990]

Hey All! So I've been having what I'm considering is a small issue with my car. I bought it a couple of months back (2004 A4 1.8T FWD) and had the CEL on(I checked the code and it has to do with the CAT Converter). Guy was selling it for a good price and i decided to pull the trigger on it, but Anyways back to the issue. The temp gauge has been staying or going back to the "C" during my commute to work whenever is 75 or less degrees outside and it won't heat up as long as i am driving.

I did some searching on Google and found a few suggestions:
- Thermostat broken / not working properly
- Coolant Temp Sensor (Supposedly this might contribute to the CEL being on? or maybe the thermostat?)
- Temp Sensor (I'm assuming is the same as coolant temp sensor?)

Also i found out by my mechanic that the one of the fans on the car isn't working properly. I'm currently working on replacing Could this also be something that would affect the temperature even in the cold? I hope i can get some help from you guys!


Thanks,

Lopez!

[A4Maine-iac]

Does it go up when sitting? If so I lean towards the CTS. If it stays mostly on C I lean towards Thermostat. Probably about time to change both out any way and you O2 sensor.

[elopez_1990]

Does it go up when sitting? If so I lean towards the CTS. If it stays mostly on C I lean towards Thermostat. Probably about time to change both out any way and you O2 sensor.

It Does Actually. Once I'm at a light or something making me stop for a few mins the needle starts going up right until i start driving again. So you would recommend me changing both items along with O2 sensor?

[Jflow23]

You can try a new green coolant temp sensor...like 10-15 bucks on ECS. It will most likely not fix your problem...but it's a cheap fix. Your problem is most likely the thermostat...it's not a terribly painful job, there is a DIY on here that I followed. Recommend you do the j-plug w/ the thermostat. I got my thermostat from Rockauto...lucked out, it was an OEM part with the Audi SN scraped off. My thermostat only had ~60k when it failed but it was ~9 years old.

[SlickFix]

Sounds like a thermostat to me, too. But, you should also check to see that your radiator cooling fans are not stuck on all the time.

[SJorge3442]

for a 1.8, sounds like a thermostat, especially since its electronically controlled and not dependant on Wax like most other thermos. BUT! A failing coolant temp sensor can cause issues with the thermostat function. I say start with the sensor, then go from there.

[old guy]

Just an FYI. The thermostat opens mechanically just like any other thermostat. It also has a heating element in the wax that allows the ECM to force the thermostat open under certain conditions. Sounds to me like a faulty thermostat.

[ECS Tuning-Audi]

If the vehicle isn't overheating at all but the gauge just acts sporadically chances are its the coolant temp sensor.

It's located on in the coolant flange at the back of the head near the fire wall. We have them available below.

Click HERE to order or for more information


Jason

[SJorge3442]

Just an FYI. The thermostat opens mechanically just like any other thermostat. It also has a heating element in the wax that allows the ECM to force the thermostat open under certain conditions. Sounds to me like a faulty thermostat.

thanks for the knowledge!

[SlickFix]

OP, whatever you end up replacing, make sure to buy OEM Audi/VW parts. I've had too many third party knock off parts fail on me, so now I buy OEM exclusively. Well, most of the time, anyway.

[ZipMeUpJ]

For the tstat behr Is the oem supplier. Buying a behr is just the oem with the rings scratched off and about $60 less. Same part number I think

[elopez_1990]

You can try a new green coolant temp sensor...like 10-15 bucks on ECS. It will most likely not fix your problem...but it's a cheap fix. Your problem is most likely the thermostat...it's not a terribly painful job, there is a DIY on here that I followed. Recommend you do the j-plug w/ the thermostat. I got my thermostat from Rockauto...lucked out, it was an OEM part with the Audi SN scraped off. My thermostat only had ~60k when it failed but it was ~9 years old.

This is what i had in mind. But didn't want to make the move until i had a few opinions about changing it! And i do appreciate the tip for the J-Plug. I will go ahead and replace since i'll be doing some work the thermostat

[elopez_1990]

Sounds like a thermostat to me, too. But, you should also check to see that your radiator cooling fans are not stuck on all the time.

Actually the fan doesn't turn on at all sometimes. My mechanic said he thinks the fan is just old and needs replacement. Plus i checked them and the big fan, I think, does not move at all.

[elopez_1990]

for a 1.8, sounds like a thermostat, especially since its electronically controlled and not dependant on Wax like most other thermos. BUT! A failing coolant temp sensor can cause issues with the thermostat function. I say start with the sensor, then go from there.

Its what i had in mind. or at least what i could put together from the Google Searches.. I will go ahead and do it on this order! Thanks man!

[elopez_1990]

Just an FYI. The thermostat opens mechanically just like any other thermostat. It also has a heating element in the wax that allows the ECM to force the thermostat open under certain conditions. Sounds to me like a faulty thermostat.

I gotta say i am a little lost with this info.. What do you mean by WAX?

[elopez_1990]

OP, whatever you end up replacing, make sure to buy OEM Audi/VW parts. I've had too many third party knock off parts fail on me, so now I buy OEM exclusively. Well, most of the time, anyway.

Oh yeah! I always do! I don't like taking my chances with knock off parts!

[elopez_1990]

For the tstat behr Is the oem supplier. Buying a behr is just the oem with the rings scratched off and about $60 less. Same part number I think

Thanks for the info man! I will look into this.. I usually buy them at VWPARTS2GO.com they have like a 20 or 30% off from the dealer price.

[AudiA4_20T]

Actually the fan doesn't turn on at all sometimes. My mechanic said he thinks the fan is just old and needs replacement. Plus i checked them and the big fan, I think, does not move at all.

Your mechanic doesn't know these cars

[AudiA4_20T]

If the vehicle isn't overheating at all but the gauge just acts sporadically chances are its the coolant temp sensor.

It's located on in the coolant flange at the back of the head near the fire wall. We have them available below.

Jason

Really Jason? Come on dude you're better than that. It's obviously not his CTS that's faulty. If you're gonna push parts at least push the right ones.

[old guy]

I gotta say i am a little lost with this info.. What do you mean by WAX?

Here is how a conventional thermostat operates. A map controlled thermostat is created by adding a heating element to the wax capsule so the ECM can apply power to the heater and force it to open sooner and or stay open longer depending upon specific engine conditions. Without power to the heater the thermostat will still open once it reaches the required temperature.

[ECS Tuning-Audi]

Really Jason? Come on dude you're better than that. It's obviously not his CTS that's faulty. If you're gonna push parts at least push the right ones.

It's a honest suggestion. I had an issue with my B6 around this time last year. Coolant temp gauge would work and sometimes not work. It would sometimes stay on the C and then jump to the first notch then to cold again. Or sometimes it wouldn't budge.

My car never overheated and I still had heat. After a while it led to starting issues when it got colder. Replaced the CTS and it fixed the issue.

Not to mention that sensor is directly related to the gauge. You can always pull it first and test it's resistance. Pull codes as well, this would be the for sure way to tell.

Just saying it might not always be the thermostat.

Jason

[elopez_1990]

Your mechanic doesn't know these cars

I don't disagree with you sir.. I usually tell him what to do Since i don't have many tools in my collection yet. He does the labor for me haha

[elopez_1990]

Here is how a conventional thermostat operates. A map controlled thermostat is created by adding a heating element to the wax capsule so the ECM can apply power to the heater and force it to open sooner and or stay open longer depending upon specific engine conditions. Without power to the heater the thermostat will still open once it reaches the required temperature.

Wow this is really nice to know. You definitely know what your doing sir! I've seen a couple of posts from you and you seem very knowledgeable!

Also, I see that you own a VW CC? I had one of those before the A4, they're awesome cars! the most complemented car I've owned to date!

[old guy]

My CC VR6, like my A4 is also approaching 200K miles. It has been pretty much bullet proof. It still has the original front brake pads! All I've done is mostly routine maintenance. Replaced the rear pads and rotors. I had to replace the wiring harness for the trunk lid because of broken wires but the complete harness was only around $80. Then a bulb or two. A parking sensor. That's about it. The chipped VR6 is a pretty impressive engine.

Same color as this with the 18 Interlago wheels.:

[EastTNPharmD]

Just a word of advice I wish I had been given when I changed my fans. When you place the car in service position and have to drain the fluid, replace the lower coolant temp sensor before you fill it back up. I'm living with a CEL cause I don't have the time right now to drain and refill. Also your issue sounds exactly like what I was dealing with. Turns out the thermostat was stuck open (not closed as traditionally they are) and apparently because of the fluctuation it would give it kept the fans running a lot more then they should have. Now did that cause my fan failure? My car has 160+ on it they were probably due, but definitely didn't help. Just my .02


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[DiertyEuroSpec]

First replace the coolant temp sensors. There's two one under the car (The sensor you pull to drain your fluid) and one at the rear of the motor in the coolant flange. Both are very easy to replace and if you haven't done so already will help the engine run smoother especially on cold starts. If that doesn't fix it and I am thinking it wont then you've got to do the thermostat, which is kinda PITA to replace because you've got to remove the intake manifold. Either way this will refresh all your cooling control components and is not a very expensive repair at all.

I would buy all parts together also just replace in that order. GL

[old guy]

First replace the coolant temp sensors. There's two one under the car (The sensor you pull to drain your fluid) and one at the rear of the motor in the coolant flange. Both are very easy to replace and if you haven't done so already will help the engine run smoother especially on cold starts. If that doesn't fix it and I am thinking it wont then you've got to do the thermostat, which is kinda PITA to replace because you've got to remove the intake manifold. Either way this will refresh all your cooling control components and is not a very expensive repair at all.

I would buy all parts together also just replace in that order. GL

Actually it is pretty straight forward to do without removing the intake manifold. Clicky click

[DiertyEuroSpec]

I stand corrected, and as always thank you OG.

[diagnosticator]

Sounds like a thermostat to me, too. But, you should also check to see that your radiator cooling fans are not stuck on all the time.

Even if the cooling fan was stuck on high speed, running all the time, the engine would run at the normal operating temp, unless the t-stat was stuck open. The t-stat controls engine coolant temp unless the t-stat is open, not the cooling fan.

[elopez_1990]

Thank you all! This definitely gives a weekend project now. Old Guy, thanks for the link on the DYI! very helpful!

[elopez_1990]

My CC VR6, like my A4 is also approaching 200K miles. It has been pretty much bullet proof. It still has the original front brake pads! All I've done is mostly routine maintenance. Replaced the rear pads and rotors. I had to replace the wiring harness for the trunk lid because of broken wires but the complete harness was only around $80. Then a bulb or two. A parking sensor. That's about it. The chipped VR6 is a pretty impressive engine.

Same color as this with the 18 Interlago wheels.:

Wow! That's a lot of miles on both cars! I need to make that a goal and reach for the same amount! Very nice car by the way, mine was white with the 2.0T Luxury trim. That Dynaudio sound system was very nice!