TDI “Slowly” Overheating

[Huckfinndy]

I purchased my 2014 Passat TDI SEL in March 2019 from a VW dealership. It was CPO because it received the emissions fix from VW. Because it was a CPO TDI it received the 2yr Unlimited Warranty from VW. From March 2019 - August 2021 I never saw the temp gauge “slow creep” past 190°. Beginning on September 4, 2021 on a one hour trip across a flat Highway road it began to “slow creep” up over 190°. I contacted the VW dealership where I purchased the vehicle and the Service Manager and I discussed the issue. At the time, the thought process was the temp changes could be related to the TDI completing a regen. Fast forward a few weeks and the TDI continues to have the overheating issue. I contacted The VW dealership and had them take a look at it on October 11, 2021. They scanned with the computer and completed a manual regen at my request but ultimately said it is not showing signs of overheating. On the way home from the dealership the TDI overheated twice. I returned to the VW dealership on October 16, 2021 to drop it off so they could look at it again. While at the dealership the TDI did overheat for them. While troubleshooting they found that the fans were randomly shutting off. This was covered under the CPO warranty so they replaced the fans. Unfortunately, they found that the fan replacement did not solely fix the overheating issue. The next day an identical Passat came into the dealership for service not related to overheating issues. the same year year and engine They ran a comparison test with them. Both went on identical 35 minute trips and both pulled the same temps for the block and coolant temps with scan tools. Originally, the dealership thought the temps were too high even after the fan replacement; however, they got VW tech support involved. VW tech support said temp fluctuation is normal in a TDI and if it’s only going up to 210 or 220° VW doesn’t consider it as overheating. They said as long as I was not operating the vehicle in the “red line” it should not cause any engine damage. At this point, the dealership believes that the replacement fans did fix the issue because per VW tech support it is normal for the temps to fluctuate. The dealership assured me that all is documented with them and with VW tech support in case something occurs in the future concerning the overheating. Well I picked up the car from the dealership on October 22, 2021 and it overheated three separate times on my two hour + trip home. I took pictures of the temp gauge just like I have previously in case any further action is needed.
I guess my issue is that a vehicle occasionally overheating does not seem right to me….I think that following the emissions fix VW is “washing their hands” of the TDI’s in the U.S. Anyone else have similar issues or experiences with their TDI overheating? Anything that was brought to your attention that differs from what I experienced? My plan is stay in constant contact with the dealership in case the TDI engine goes south….

 

[Lightflyer1]

You never said if it was setting a code or not. If so what code? Warranty will only cover items that set a check engine light. Some dealers are reluctant to help much. Some others do much better. Luck of the draw. It just pays to know the warranty and know the car. My Beetle also operates in these higher temps at times but no codes or check engine lights or other adverse effects. I think it is considered normal as long as it isn't throwing codes.

 

[Huckfinndy]

You never said if it was setting a code or not. If so what code? Warranty will only cover items that set a check engine light. Some dealers are reluctant to help much. Some others do much better. Luck of the draw. It just pays to know the warranty and know the car. My Beetle also operates in these higher temps at times but no codes or check engine lights or other adverse effects. I think it is considered normal as long as it isn't throwing codes.

Sorry I did forget to mention anything about codes. It was not showing any codes and the dealership was very quick to point out that unless it was showing a code most things are not covered under warranty. Thank you for the response.

 

[TurboABA]

Why do you think it's overheating? Have you had any idiot lights pop up or has it gone into limp mode or anything like that? Is your coolant boiling or anything?

 

[Huckfinndy]

I am basing my overheating solely from the temp gauge reading (it goes up to about 220°). I will try and attach a picture if I can figure out how. I have not had any other idiot lights come on. As far as the coolant boiling not that I am aware of. When the dealership tested the temps in the block and coolant tank they said they were ok.

 

[TurboABA]

Temperature gauges are supposed to fluctuate as temps are never rock solid..... VW purposely programmed the gauges to be dumb (read not react or be very accurate) so that people like you don't worry about a system temp that's not constant. Unless you're having actual signs of overheating, quit being so fixated on a needle that you think should always stay pointing north no matter what.

Lastly, when was the last time you had a coolant system flush?

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[Windex]

VW's temperature gauges are notoriously inaccurate. If your car was mine, I would do two things.

1 buy a scangauge or similar scanner and get the temp reading directly from the ecu.
2 buy an inexpensive IR thermometer and take the engine temp at the upper rad hose when you suspect it is overheating.

The two above will conclusively tell you if you actually have a problem, or if this is just a gauge inaccuracy. Additionally, you will know if the Engine coolant temp sensor is reading accurately.

Has anyone checked the thermostat for proper operation? Conirmed there's no dirt or debris partially plugging the rad?

 

[Lightflyer1]

The newer cars I guess have actual gauges or at least mine does. It is in the MFD and in the dash pod gauge. Reads out in actual degrees. It is very accurate and matches VCDS.

 

[06bluebeetletdi]

My ‘14 runs around 215* on the scangauge, it will go past 220* during regens in the summer (95*+) the gauge on the cluster stays at 190.

 

[Huckfinndy]

Here is a picture of the temp

210°

• Huckfinndy
• Nov 4, 2021

Here is a picture of my Passat as the temp gauge was rising to 210°

 

[Huckfinndy]

My ‘14 runs around 215* on the scangauge, it will go past 220* during regens in the summer (95*+) the gauge on the cluster stays at 190.

I am not sure what it runs on a scangauge because I do not own one. With that said, I should probably buy one. I have only ever noticed the temp gauge in the instrument cluster going up while driving. I have owned the car since March 2020 and until September 2021 never had the temp gauge move past 190° while driving in PA summer temps (80-90° on average). I think I have a general understanding of the regen process which is why I consider this issue unusual. My car does this several times per week and never did this prior to September 2021.

 

[Huckfinndy]

The newer cars I guess have actual gauges or at least mine does. It is in the MFD and in the dash pod gauge. Reads out in actual degrees. It is very accurate and matches VCDS.

That is interesting. I don’t know if mine has that but I will check tomorrow in the am.

 

[Huckfinndy]

VW's temperature gauges are notoriously inaccurate. If your car was mine, I would do two things.

1 buy a scangauge or similar scanner and get the temp reading directly from the ecu.
2 buy an inexpensive IR thermometer and take the engine temp at the upper rad hose when you suspect it is overheating.

The two above will conclusively tell you if you actually have a problem, or if this is just a gauge inaccuracy. Additionally, you will know if the Engine coolant temp sensor is reading accurately.

Has anyone checked the thermostat for proper operation? Conirmed there's no dirt or debris partially plugging the rad?

That is a good idea. I will look into purchasing a scanner and thermometer. I originally thought the thermostat may not have been functioning properly and asked the dealership to test it. I was told by the dealership that they tested the thermostat with the computer and it was functioning fine in October. I believe they should have pulled the thermostat and physically tested its operation but that did not happen.

 

[Lightflyer1]

I am in a Beetle so it may be different. Digital temp readout on the mfd for water and gauge readout for oil temp in the dash pod.

 

[TurboABA]

Have your coolant flushed before you spend on tools. It's not a lifetime item.

 

[oilhammer]

The CKRAs are starting to be notorious for messed up cooling systems. It starts with clogged heater cores (there is a TSB about this), but it proceeds to failing thermostats and clogged radiators (both for the engine and the intercooler). The other new trick up the CKRA sleeve is the cracking oil filter housing (they are plastic, and they crack exactly like the EA888 gasser engines' water pump housings).

The overheating will get worse, it'll eventually start pegging the gauge when under load.

I'd start with a thermostat, and while you are in there, a new oil filter housing. Huge job, but both those items are in there and can be done together. I also have a dipstick tube on hand (those can be brittle and break when the come out), and the coolant pipe o-ring. And if your car has the plastic water tube, replace it with the new metal one while you are in there (it has to come off anyway).

Closely examine the condition of the block inside where the thermostat assembly sits. It should be a clean, uniform, medium gray color. If it is rusty orange, or brown, or if there is a bunch of debris jammed in the thermostat (you can take the old one apart and see), then you may be wanting to replace both radiators.... but you can certainly try flushing them with the garden hose.

 

[TurboABA]

Here's the TSB that @oilhammer is referencing..... I suggest taking that into your dealer and saying that your passenger side heat is insufficient in order to get the system flushed out.

https://static.nhtsa.gov/odi/tsbs/2016/MC-10106581-9340.pdf

 

[tristan81491]

If your car and the identical Passat ran on the same loop and brought back the same #s, could it just be that the temp gauge itself is wonky? Is there something in VCDS that can calibrate it? I agree with folks that the temp gauge is a dummy gauge. My scan gauge tool in my MK4 TDI showed a number that fluctuated, my Polar FIS also did the same in my MK6 Golf

 

[oilhammer]

The gauge doesn't fail. The Instrument module is just displaying an average of what it is told to do via wherever it gets that information from (varies by model). This is normal. All modern cars that actually have a temp gauge do this. Otherwise, the gauges WOULD fail, because they'd wear themselves out going up and down all the time!

This is why whenever suspecting a temp control issue, diagnostics must involve first monitoring the data available in the various modules, and understanding where exactly that data is coming from. Some cars have a sensor that provides the signal to the ECU, another that provides a signal to the Instruments. In some cases, both those circuits are physically contained within one sensor, but have no interaction with one another. Some cars only use one sensor, and that provides the data solely to the ECU, then the ECU in turn broadcasts this value across the CAN bus and all the modules that require it (Instruments, HVAC, Trans, etc.) have access.

I also think it helps to have a baseline to work from. It can be difficult to tell if something is broken if you don't know how it is supposed to work when it ISN'T broken. Not knowing this often sends people chasing their tails in a diagnostic dead end.

 

[TiddyAye]

Great info on this thread. I've been fighting with the cooling system on a new-to-me 2014 Passat TDI. It'll maintain a steady 190 while idling in my driveway but even a short drive of a mile it gets too hot and shuts down. I've already replaced the oil cooler and the heater core and flushed the system as well as possible but it still overheats. I have a new thermostat assembly and I've ordered a new radiator and after reading Oilhammer's comments I'll add this to the list:
-intercooler radiator
-oil dipstick tube
-coolant pipe o-ring
-replace plastic water tube with metal one

Is there anything else? Trans cooler? Which plastic water tube can be replaced with a metal one?

Thanks!

 

[oilhammer]

Your 2014 most likely already has the metal tube from the factory.

I'd probably get a new oil filter housing while you are in there. Those like to fail without warning, and are not easy to get at unless you already have everything loose.

 

[TiddyAye]

Thanks for the reply about the metal tube and all the other info, much appreciated.

I said "oil cooler" but I meant to say I replaced the entire oil filter housing assembly with the oil cooler on it. The original one failed without warning just as you said. The plastic was melted to the point that the oil filter cap stem was stuck inside the housing and it snapped when I unscrewed the cap. The oil passage walls were also obviously melted and failed. When all the parts arrive I'll take the housing back off and inspect it to make sure there hasn't been damage to the new, I hope not because I paid for the OEM one. If it's damaged I'll get an aftermarket version for a quarter of the price.

 

[bhdeloach]

Hey, did the new parts you replaced on your Passat fix the overheating issue? My 2014 Passat TDI started doing the exact same thing with the overheating. I just had the heater core replaced under the extended warranty and it started overheating on a long trip down to FL this weekend. Like yours, mine will idle all day with the A/C on and stay at 190 degrees. If i get on the interstate and get to 65 it starts to climb all the way up to the redline withing two miles. What's funny is as soon as I pull over the temp starts to come right back down within a minute or so. If I turn the car off right then and crank it back u the temp gauge returns to where it was at 250 but immediately starts to go back to 190 and the process starts all over again as soon as I get on the road. On Saturday it stayed at 190 as long as I was driving around on the city streets at 45 MPH or less. I did leave the radiator cap off in the parking lot for probably 30 mins to make sure the system was able to bleed out any air that may have been in the system just in case the dealership didn't get it all out - no change. HELP!

 

[Highwaylizard]

Have a very similar situation. Car does fine in town but gets hot on the highway. Used to run at 191-193 degrees and now runs at 200-204 degrees. At the same time my tank average has gone from 42 MPG down to 36 MPG. Car also seems to have less pep. Taking the car into the shop tomorrow but they cannot get to it for at least two weeks. I cannot keep driving it like this as I feel like I am running on borrowed time.

I scanned it and found no codes.