Strange Cooling System Behaviour

[gholl]

The engine in my jetta is a 2.0 TDI 140 PS and the cooling system has been behaving strangely for the past year or so. It never reached a correct operating temperature and the gauge rarely moved off the minimum. The garage replaced the thermostat, but couldn't explain why the engine never really warmed up, even though the fans would come on for no apparent reason every now and then. After looking through the other forums for models with similar engines I realised it could be the thermostat for the DSG gearbox. The mechanic had never realised there was one. This was replaced and there was some improvement, in that the temperature would come up to normal (90), but only when ticking over with the heater off. The tickover RPM has settled down to around 750. It was jumping up to almost a 1000 at times. Drive off and the temperature comes down. Use the heater and it comes down. However, the gearchange is less clunky now. I can remove the expansion tank cap at anytime with no spitting of hot water or bubbling.Does anyone know what causes this behaviour as it appears to me that the engine is not generating enough heat?
regards, Graham

[Crasher]

The gauge cannot be used as a reference, it reads 9pm at 77 and still reads it at 117; it needs to be studied in the engine and instrument measuring blocks. Do you have any info on the parts fitted and what is the VIN?

[gholl]

Guaranteed genuine VW parts fitted. The replacement DSG thermostat was ordered after the original part was removed. If I remember correctly the part number ended in something like ...13. The electric pump used to divert (I think) heater water was found to be working. The VIN is WVWZZZ16ZBM124286. Thanks

[Crasher]

Did he fit the revised DSG thermostat assembly 1K0 122 101 KP or just the thermostat 1K0 121 113 A and was the thermostat the revised version 03L 121 111 AL instead of 03L 121 111 AE?

[gholl]

Hello Crasher

Just the DSG cooler thermostat 1K0 121 113A. The main thermostat was just a part for part replacement, genuine VW sourced. Don't know a thing about the revisions. I presume these weren't related to recalls, because the only records I have are related to seat bolts and dieselgate.

[Crasher]

There is another chap on forums who I am trying to help/failing with the same odd problem and all I can suggest is going back to fitting a new genuine VW revised 2 way thermostat 03L 121 111 AL. Sometimes you have to go back to the beginning.

[gholl]

Thanks, Crasher. I'll try this.

[gholl]

p.s. What's the difference beteween the AE and the AL?

[Crasher]

An internal unspecified revision I would think.