# Very High Coolant Temperature - V8 Engine



## j3w (Feb 7, 2012)

Okay, I did a little research and I think this will end up being a thermostat or water pump ish...but I wanted to throw it out there, explain and then I'll follow up with a diag from my dealer.

I bought my 2004 Phaeton V8 with 40k miles on the clock.

Sidenote, having too few miles on an older car seems to be as bad as having too many? Ugh.

Anyway I parked the other night and noticed that the Phae was a little loud, both fans were running full blast. I didn't pay attention. A night or two later I was out driving and it was about 76 degrees, the temp gauge slowly climbed from it's normal 200 degrees water temp up to 240, 260, 280, but NOT into the red zone.

I got where I was going - maybe 15 miles. Came out 2 hours later and drive to another location, same thing. Temp climbed up, up, up but didn't redline.

Next DAY it was extremely hot here, 101 ambient. I drove about 5 miles before it climbed to 260.

So...so far it's not overheated yet, but the water temp is really, really high. I looked in the manual and it said that 200 degrees is normal, but there is a further bit - the manual says that as long as the temp is NOT in the red "don't worry".

So...any input, guys?


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## j3w (Feb 7, 2012)

Coolant is pink and topped off, btw.

Just turned over to 50,000 miles.


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## Jxander (Aug 5, 2008)

j3w said:


> Okay, I did a little research and I think this will end up being a thermostat or water pump ish...but I wanted to throw it out there, explain and then I'll follow up with a diag from my dealer.
> 
> I bought my 2004 Phaeton V8 with 40k miles on the clock.
> 
> ...


It's probably your thermostat. The 4.2l V8's thermostat seems to be a bit of a problem as miles or possibly time pass. This is true not just for the Phaeton but also the Touaregs and Audis that have the same engine. 

However, as another possibility I experienced the same phenomenon two different times but it has never happened since. I attributed mine to having the coolant replaced but the system not bled correctly. My guess is that the heater valves were not opened, so the flush was complete and I had a bubble in the heater core or line. My problem occurred when I turned my heater on for the first time in approximately a year ( I live in Florida). Since then I periodically turn my heater up to max temp irregardless of the outside temperature so that I get coolant flow through the heater cores. 

If it is determined to be a thermostat, you may want to consider doing the timing belt, water pump and related parts normally included in the timing belt service. To get to the thermostat is fairly labor intensive and the work is somewhat redundant if you do the timing belt and/or water pump at a later time. There's much discussion about the lifetime of the timing belts on Phaetons. VW officially recommends 80k and I've heard age or time in service is also an issue. For a typical driver of 15k per year, 80k miles would be 5+ years. Since a 2004 Phaeton is roughly 8 years old, it's probably time for the timing belt service despite low miles. I know a risk of belt failure is there but it is your dime and obviously your decision. 

Despite some of the problems of low mileage cars, I'd still prefer low over high.  Sounds like you found a good one.

Jim X


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## j3w (Feb 7, 2012)

Jxander said:


> Sounds like you found a good one.
> 
> Jim X


Two weeks after I took delivery the tranny sheared 3rd and 4th gear.

$7000.










Just went for a drive and the coolant temp rose to here, and stayed for a good half hour of driving at about 50 mph.


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## ArtWarshaw (Feb 15, 2006)

*Coolant Temp*

Had a similar experience a couple of years ago - drove it straight to the dealership. New thermostat fixed the problem


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## Jxander (Aug 5, 2008)

j3w said:


> Two weeks after I took delivery the tranny sheared 3rd and 4th gear.
> 
> $7000.
> 
> ...


Ouch - sorry about that. I also had a tranny replacement due to harsh shifting and an eventual episode of limp mode. I was lucky that mine occurred while I was still under CPO warranty. Was the transmission replacement recently? If so make sure the cooing system was bled properly. Probably not as likely as a flawed thermostat but it is possible and much cheaper to remedy than the thermostat replacement. 

I also noted your oil temperature gauge is registering abnormally hot. Thus, this is definitely not an issue with the coolant temp gauge or temp sensors. Probably not wise to continue driving until problem is resolved.

Jim X


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## j3w (Feb 7, 2012)

I have an appt tomorrow, so will report back.


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## j3w (Feb 7, 2012)

Jxander said:


> It's probably your thermostat.


You win the prize...I was afraid of this.



Jxander said:


> If it is determined to be a thermostat, you may want to consider doing the timing belt, water pump and related parts normally included in the timing belt service. To get to the thermostat is fairly labor intensive and the work is somewhat redundant if you do the timing belt and/or water pump at a later time. There's much discussion about the lifetime of the timing belts on Phaetons. VW officially recommends 80k and I've heard age or time in service is also an issue. For a typical driver of 15k per year, 80k miles would be 5+ years. Since a 2004 Phaeton is roughly 8 years old, it's probably time for the timing belt service despite low miles. I know a risk of belt failure is there but it is your dime and obviously your decision.


Gonna do the whole show....ugh.


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## Jxander (Aug 5, 2008)

Hopefully you'll have many miles of good motoring after this and some return on your investment. 

Best of luck.

Jim X


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## invisiblewave (Sep 22, 2008)

Make sure you carefully check the bumper cover after they've done the job. Look very closely for cracks, and check the operation of the headlamp washers. Also check the wheel well liners and headlamp alignment (by which I mean the physical position of the headlamp units and the panel gaps around them).


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## Reflect (Apr 4, 2007)

just need to go get a new thermostat and in teh process do the water pump etc. the dealer will inform you, it wasnt to expensive when i did it but it was done under warranty right around 50k like you. it happened to many of us but easy fix


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## Phaeton_qatar (Jun 20, 2012)

I have the same problem that J3W reported in the first thread. The coolant temp goes above 90C. I suspect it is the thermostat failure but want to confirm using the VCDS Scan. Which option in the VCDS will show the status of the thermostat and water pump? what steps do I need to follow?

Thanks
Asad


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## invisiblewave (Sep 22, 2008)

There are two measuring blocks to look at. I don't recall which, but if you have the genuine software it gives you a list, and the ross-tech website will also tell you. It shows the temperature readings from the two coolant sensors. Mine rise together, which I suspect indicates that my thermostat is stuck open, which I think is preferable to it being stuck shut, but I'm also suspicious that the tool isn't working correctly.


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## Bindaham (Apr 4, 2014)

Phaeton_qatar said:


> Which option in the VCDS will show the status of the thermostat and water pump?


Salam Asad, 

Try this sequence for the pump.

Regards,

Salah


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## Phaeton_qatar (Jun 20, 2012)

> Try this sequence for the pump.


Thanks Salah for the steps. this is useful for pump testing.



> It shows the temperature readings from the two coolant sensors. Mine rise together, which I suspect indicates that my thermostat is stuck open


Thanks invisiblewave. I did find more then 2 coolant monitoring values. They all show equal temperature while rising. does this mean that thermostat is not working ?


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## Bindaham (Apr 4, 2014)

This is an amazing write up by Michael (as usual) that might be useful.

This is for the W12 but nevertheless, the information is interesting. 




PanEuropean said:


> Hello All:<p>I reported the other day that my 'Check Engine Light' had illuminated - this was the first time that I have ever seen this light come on in over 2 years of Phaeton ownership. So, I dropped by my VW dealership and the technicians read the fault code out from the engine controller memory - it indicated that the F265 Map Controlled Engine Thermostat Replacement was showing an 'open circuit' condition. The consequence of this was that the engine was running quite hot (about 110°C, or 230°F). <p><B>Fault Code Generated by the Failed Thermostat</B><br>
> 
> 
> 
> ...


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## Phaeton_qatar (Jun 20, 2012)

> This is an amazing write up by Michael (as usual) that might be useful.
> 
> This is for the W12 but nevertheless, the information is interesting.


Yes, Michael does awesome in detailing. I read this earlier but it did not help me since my VCDS full scan is not showing any error relating to water pump or thermostat. In Michael post, the Scan is pointing to thermostat issues. 

The link you sent earlier is probably for testing Aux pump however I will still try that out tonight when I go home  .


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## invisiblewave (Sep 22, 2008)

Phaeton_qatar said:


> Thanks invisiblewave. I did find more then 2 coolant monitoring values. They all show equal temperature while rising. does this mean that thermostat is not working ?


I wish I could tell you for sure, because that's exactly what mine do too. Mine doesn't overheat though. If they're both rising, I THINK that means that the thermostat is open, which would cause the engine to run cold after starting, not to overheat.


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