Suspected Thermostat Issue - Opinions?

[f00glee]

As the weather's got a little cooler I notice my temperature gauge between the clocks sometimes wanders a minor division below 90 when cruising. Climatronic display see temps hovering between 70 and 75C unless driving hard or in traffic. Done a little reading and decided to monitor coolant temperature sensors from cold.

Both radiator and engine temp sensors started at 18C, suggests sensors are ok.

After 10 mins engine is at 65C and radiator 20C, so assumption is thermostat closed.
At 67C suddenly the radiator temperature started to climb, assumption is thermostat opened.

diagnosis: thermostat needs replacing? I don't seem to have an inline stat at all in front of the engine. I understand this is normal for 06 onward cars? Also manual so no stat for DSG. Therefore main stat is the only culprit?

I've had thermostats stick open/shut completely on previous cars, but never seen this early opening behavior. Not knowing exactly how they work, would guessing that a spring or whatever holds them shut till 87C (i think this is the spec) has weakened be reasonable?

[Octoparrot]

Sounds like the thermostat, mine never had an inline one, also 06 manual. As a precaution I changed both sensors as well, the one on the thermostat housing looks a pig to get at in situ so possibly consider changing this one.

[f00glee]

So TPS had the parts on Saturday, had a whole Sunday free to do the work - and I needed all of it! 8 hours (much of which fighting silly things, like spring clips and seized pipes) later and job done.

First run up to temperature saw much nicer engine & radiator temps, with the thermostat operating in the high 80s now.

Took the car for a shakedown run and heard a loud PUNGGG noise - blew a turbo hose off! Either a damaged connection or not fitted properly. Made it home by unplugging MAF and have left if to pick up after work today. 

Hopefully another hour to sort and we'll be back in business!

[Octoparrot]

So TPS had the parts on Saturday, had a whole Sunday free to do the work - and I needed all of it! 8 hours (much of which fighting silly things, like spring clips and seized pipes) later and job done.

First run up to temperature saw much nicer engine & radiator temps, with the thermostat operating in the high 80s now.

Took the car for a shakedown run and heard a loud PUNGGG noise - blew a turbo hose off! Either a damaged connection or not fitted properly. Made it home by unplugging MAF and have left if to pick up after work today. 

Hopefully another hour to sort and we'll be back in business!

Yep mine took me that long for the exact same reasons.