Why I installed a low temp thermostat.

[pothole]

Originally Posted by Chuck W.

Can someone answer this? TIA.

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.

[JFP in PA]

Originally Posted by pothole

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.

The stat set the minimum or baseline coolant temperature the car is going to run at and return to when cooling off from a higher temp like when stuck in traffic. Because the stat consistently lowers the baseline temp of the coolant, it also lowers the oil temps as well, which is even more important.

As for why people don't see much movement in the dash gauge when using one, that is simply due to the grossly inaccurate and non linear nature of factory gauge, which is little more than an idiot light with a pointer.

[pothole]

Originally Posted by JFP in PA

The stat set the minimum or baseline coolant temperature the car is going to run at and return to when cooling off from a higher temp like when stuck in traffic. Because the stat consistently lowers the baseline temp of the coolant, it also lowers the oil temps as well, which is even more important.

Sorry, I can't see how you are correct.

Let's say you're stuck in traffic crawling for an hour. Essentially no natural airflow over the rads.

The low-temp stat car will start off at a lower temp. I agree on that. But pretty quickly, the coolant temp will rise to that of the full-open temp of the standard stat. That will happen within about five mins of sitting in traffic. From there on in (again, in this stuck-in-traffic scenario), you have a cooling solution that will operate just like the standard car.

Of course, in that five minutes, the standard car will have gotten hotter. And it will be first to trigger the fans. But once the low-temp stat car has triggered its fans, both cars will just cycle their fans on and off.

For the low temp stat to reduce coolant temps in this scenario, you would have to lower the trigger and shut-down temps for the fans. But these are higher than the full-open temps for the standard stat, much less the low temp stat. So, in both cars, you are cycling the fans with the stats full open.

Thus, the oil temp in the low-temp stat car will start a bit lower than the standard car, but it will quickly catch up.

[JFP in PA]

Originally Posted by pothole

Sorry, I can't see how you are correct.

Let's say you're stuck in traffic crawling for an hour. Essentially no natural airflow over the rads.

The low-temp stat car will start off at a lower temp. I agree on that. But pretty quickly, the coolant temp will rise to that of the full-open temp of the standard stat. That will happen within about five mins of sitting in traffic. From there on in (again, in this stuck-in-traffic scenario), you have a cooling solution that will operate just like the standard car.

Of course, in that five minutes, the standard car will have gotten hotter. And it will be first to trigger the fans. But once the low-temp stat car has triggered its fans, both cars will just cycle their fans on and off.

For the low temp stat to reduce coolant temps in this scenario, you would have to lower the trigger and shut-down temps for the fans. But these are higher than the full-open temps for the standard stat, much less the low temp stat. So, in both cars, you are cycling the fans with the stats full open.

Thus, the oil temp in the low-temp stat car will start a bit lower than the standard car, but it will quickly catch up.

Unfortunately, you hypothesis is flawed. Yes, stuck in traffic, a car with either thermostat will begin to heat up, but from different starting points. The car with the OEM stat will already be in the 205-210F range while the car with the 160 stat will be in the 174-176 range (we have repeatedly tested this on cars running with a Durametric system connected and logging data). The car with the 160 stat will take considerably longer time sitting before the fans come on than the car with the OEM stat. Both will however get hot. When the car with the 160 stat resumes moving, it will cool down, as will the car with the OEM stat, the only difference is that the car with the 160 stat will cool back down to a steady state driving temp in 174-176F range, while the other car will cool down to the 205-210F range; both determined by the minimum operating temp of each respective thermostat.

Oil temps will do something very similar, as observed on instrumented cars. The oil temp on the car with the 160F stat will have a lower driving steady state coolant temp will show and oil temp about 25F lower than a car with the OEM stat. Stuck in traffic, both will heat up until their fans come on, and their oil temps will begin to rise; but as soon as the cars are driving at a steady state speed again, both will see their oil temps begin to drop as the oil transfers heat to the now cooling coolant, albeit slower than the coolant due to heat transfer rate differences. Eventually, however, the car with the 160F stat will again show oil temps around 25F or so lower than the car running the OEM stat.

Lowering the coolant temp impacts the oil temps, which has also be demonstrated in how the UOA's look on cars running them. Oil likes staying cooler, and lives longer.

[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.