Always test your new thermostat

[Thom]

A slightly high coolant temp had been annoying me since running the new engine so I have been trying to get to the bottom of it and it seems the culprit is the then new thermostat that I used, dated 2016.

Here are two photos showing L to R :
- a 71°C thermostat, dated 2020
- an 83°C thermostat, dated 1996 (off my original 2.5 engine)
- another 83°C thermostat, dated 2016 and used in the current engine.

Water at 86°C :

DSC_3099.JPG (6.98 MiB) Viewed 714 times

Water at 95°C :

DSC_3101.JPG (7.69 MiB) Viewed 714 times

The 71 and old 83 would open at their rating when the recent 83 would barely start to open at around 86°C, when both the 71 and old 83 would be fully open. The new 83 would be fully open no earlier than at 95°C. No wonder why my engine seemed to be running warmer than normal.

The new 83 also has a far shorter hysteresis than the other 2, closing completely at 80°C when cooling down when the others would still be fully open.
Interestingly the 1996 and 2020 thermostat have the same hysteresis bar the opening point. The 2016 unit will end up in the trash can (unless someone running a 944 in Alaska wants it perhaps) and the 1996 unit in the water pump.

Conclusion : always test a thermostat, new or old, before putting it into use.

[Tom]

Wow, glad you finally got to the bottom of it. I still have the used low-temp thermostat sitting in the unopened box I tried to send you years ago. The box is starting look like an antique. What brand were they all, if I may ask?

[Thom]

They're all from Wahler.
I had an issue with a Laso unit on my former 944 S2 many moons ago which was also running a little too hot and tested it to notice it would open at its rating but not as much as the Wahler (shorter throw thus less flow) , so I have been keen to only use Whaler units since then, but today's test has shown that the Wahlers should also be checked.

I'm quite pleased that the thermostat in use ended up faulty as I had been starting to think about ghetto solutions like drilling a small hole or something...

[Thom]

I went out for a long drive tonight and am quite pleased to report that coolant temp is as expected back to "normal".
Took the long way home and redid the boost settings and upped the timing... the car flies but the turbo seems too "small" or I'll probably have to just advance IVC. Only running 18 psi so far and will push it up to 22 psi. I had been neglecting that car in the last months but I must say I still love it. The big blacks brakes are stupid good, now that they work.

[Thom]

Another faulty "new" part replaced earlier this week. The aftermarket oil pressure sender used on the new engine kept showing pressures near 6 bar on the gauge under load. As the gauge started to show erratic readings recently I replaced the sender with the original unit off my 2.5 engine, dated 12.89, and pressure readings are now back to normal.