Totally agree with all of that.Thanks, yes good points - I did notice following posting this there are two versions of thermostat and my part catalogue with VIN lookup usually lists exactly the correct part but it still offered two versions JOOP 04L121113C or GEIGER 04L121113D - looking at my engine the housing I can see is the one linked to the more unusual plastic thermostat design you posted a pic of which is the JOOP version 1.
Mine is the twist to remove version 1 vs the unbolt to remove version 2.
Remove air filter housing,
Drop out coolant (which will already be done)
Remove rad cowl,
Remove couple of bolts from air pipe,
Release catch and turn coupling to remove stat - which seems simple enough! (famous last words!)
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I agree removing the entire housing would be much more involved - but kinda pointless if you are just replacing the stat.
I thought while I had the coolant dropped out I would change the stat as a precaution/preventative maintenance, my Audi 1.9 stat failed around 100k and with the OP stat failing at 44k for a £20 part I will have a go. Also with you're previous comments about finding silicates in the thermostat it will help me to flush it out more thoroughly.
If you're changing just the thermostat, it should be a far simpler process. I only had the housing done as well due to reports of them cracking/leaking. That is a far more involved job. With hindsight, I would have just done the t/stat.
Ref the t/stat - I think mine was the JOOP but can't be sure. I actually have the old housing somewhere and will try and have a look. I know TPS told my guy the `usual` one is option A and sent him that. It turned out he needed option B and that was out of stock.
Hope you get it all sorted. If I find my housing I'll post up the details.