[kjc2050]

Originally Posted by pothole

I think people are looking at buffered gauges that won't show any changes unless they are very dramatic.

You need to be looking at the temp via either the aircon screen hack or better still via the OBD port.

The lower temp stat will make a difference to the normal operating temp as when the car is cruising at speed, it's the stat that determines the operating temp, if you had no stat at all the capacity of the rads to cool would lower the temps quite a bit at a constant cruise at say 60mph.

What I'm not clear on is why the stat would help keep things cool when the car is under heavy load etc. Once the stock stat is fully open (which happens at a much lower temp than when the car is heavily stressed in any case), there's no difference between the two stats. They are both just open.

And as far as I can tell, the reason to have the low temp stat is not reduce the temps at a constant cruise. It's to stop the coolant getting really, really hot. And it's not going to do that as both stats are full open long before the temps get really hot.

I forgot to mention in my post: I was using the diagnostic capability of the HVAC control unit (Why I installed a low temp thermostat.) to get the temps. As for your other point, I used to think the same thing - "what difference would it make when the system is fully up to operating temp - both thermostats would be fully open" - but I don't believe that's the case. This is from Dempsey:

The factory thermostat starts to open at about 187° F (86° C) and only fully opens at almost 210° F (99° C).

Here's a link to the full article:

Pelican Technical Article: Boxster Water Pump & Boxster Thermostat Replacement - 986 / 987

If this is true, it accounts for the lower operating temps: the low temp tstat is opening earlier, and is wide open when the system is at "normal," fully-warmed-up temps; the standard thermostat is (likely) only partly open at that point.