New T-stat; ALH running at 85C now

[Nuje]

Did the timing belt a few months ago and replacing the thermostat at the same time - went with OEM - but didn't have anything to monitor coolant temps and the cluster was at the default "anything above 70C shows as 90C" silliness. Until now...

Was out on the freeway today at 110-120km/h and granted, it was cool (3-4C = ~38F), but during the whole drive, not once did the temp hit 90C, even going up a couple of hills (4% for ~2km). It just hung out at 84-85C the whole time. It got there fairly quickly, so I think it's just opening earlier than it should.

How much of an issue is it if the car isn't getting up to full operating temp? Is it worth it to yank it and put in a new, new one?

(BTW, this will be the third VW OEM thermostat that has been defective (in my books); the other two wouldn't open up until it was getting too hot - I discovered that on one of them by driving up to the ski hill at -5C and the coolant temp just kept on climbing up past 103C before I pulled over and felt the upper hose..which was "warm". )

 

[STDOUBT]

A while back, I switched to a higher ranged thermostat (195F/90C) on the theory "full temp is good, getting there faster is better".

I don't recall the max-scary temp to avoid (guessing 110C-ish), but have heard some old timers here state that getting a bit over the boiling point of water is good since it "dries out" your oil. Seems legit.
Another thing, if you're just going off the instrument panel gauge, you've no real idea what the actual temp is.
I always like to change the thermostat and the coolant temp sensor at the same time since a CTS on its way out will do just what you describe (hang low, sometimes even fail to rise) - adding to the uncertainty.
Check your temp with VCDS (coolant temp). I would feel OK running at 103C, but not much higher.
BTW IIRC, the OEM Tstat opens at 82C. But IMO if you never get up to 100C, that's undesirable because water will hang around.
HTH

 

[Nuje]

Thanks for the reply; that (not ever getting past 100C) was kinda the issue I was thinking I might encounter. I just don't see how I'm ever going to get up to that temp, unless I drive up to the ski hill (1000m of elevation in ~12km) at 100+ km/h mid-summerDoing the timing belt on another car recently, I looked closely at the VW/Audi-logo'd one that came out and it was stamped "87°C".

So, I would assume that's where it starts to open. And in playing around on the cooktop testing my previous "bad" OEM thermostat, that seemed to be the case (the "bad" one - on the left - didn't seem to budge until it hit ~94C - which was the water temp when I took this photo, whereas the one on the right had moved before the water hit 90C).

(And yes - temp reading was through the OBD port - first through Torque.app where I kinda had suspicions but never was driving very far, and then on my Navdy (HUD) that plugs into the OBD.