Why I installed a low temp thermostat.

[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.

[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.

[pothole]

Sorry, how was my hypothesis flawed. I clearly stated that the low temp car would start off from a lower position temperature wise.

In fact, nothing you said contradicats my point, which is that the low temp will reduce 'steady state' temps when driving, which is when you don't need to lower the temps, but not reduce temps when stuck in traffic.

At best, we disagree on how long it would take the low-temp stat car to catch up with the standard stat car when stuff in traffic.

In hot weather (which is again, when you are really looking for help with the temps), you are going to be putting on temp very fast with the car stationary or near stationary in traffic.

I would put my house on the low-temp stat car catching up within 10 mins max. From then on, you'll be in the same situation with both cars cycling fans and running at the same coolant and oil temps.

So if you got stuck in traffic for a n hour or two, the low temp stat car is going to have you running at high temp for fractionally less time. I can't see this is much advantage.

[JFP in PA]

Originally Posted by pothole

So if you got stuck in traffic for a n hour or two, the low temp stat car is going to have you running at high temp for fractionally less time. I can't see this is much advantage.

This is where your argument breaks down, you have chosen the only exceptional case where the two cars are the same, when stuck in heavy traffic, the rest of their existence, where they spend most of their life, is entirely different because they are running at different temperatures, both oil and coolant.

I don't know about where you live, but we don't spend our entire drive time stuck in slow or non moving traffic. And the difference on oil life and engine wear can bes significant

[pothole]

Originally Posted by JFP in PA

This is where your argument breaks down, you have chosen the only exceptional case where the two cars are the same, when stuck in heavy traffic, the rest of their existence, where they spend most of their life, is entirely different because they are running at different temperatures, both oil and coolant.

I don't know about where you live, but we don't spend our entire drive time stuck in slow or non moving traffic. And the difference on oil life and engine wear can bes significant

But that's the WHOLE point. The time when you want help with temps is when they are high.

With the standard stat, you are fine in normal driving. Temps are not an issue. What we want is something to prevent temps from getting too hot. Like heavy traffic.

But as soon as the temps start going up, the differences between the two stats fairly rapidly become moot.

So yes, most of the time in normal driving, the low temp stat means lower oil and coolant temps. But to no advantage because the standard car is not running very hot either!

[JFP in PA]

Originally Posted by pothole

But that's the WHOLE point. The time when you want help with temps is when they are high.

With the standard stat, you are fine in normal driving. Temps are not an issue. What we want is something to prevent temps from getting too hot. Like heavy traffic.

But as soon as the temps start going up, the differences between the two stats fairly rapidly become moot.

So yes, most of the time in normal driving, the low temp stat means lower oil and coolant temps. But to no advantage because the standard car is not running very hot either!

You don't see running coolant (and by default the oil) at 205+F all the time as running overly hot? Again, it is easy to observe the difference in how the oil feels about it as cars running the OEM stat show lower TBN values, and often have their oils "fall out of grade" at much lower mileage intervals than cars running the same oil but a lower temp stat. It is also interesting to note that Porsche's "max effort" cars, the GT2, GT3, and Turbos, all run 160F stats from the factory.

[pothole]

Originally Posted by JFP in PA

You don't see running coolant (and by default the oil) at 205+F all the time as running overly hot? Again, it is easy to observe the difference in how the oil feels about it as cars running the OEM stat show lower TBN values, and often have their oils "fall out of grade" at much lower mileage intervals than cars running the same oil but a lower temp stat. It is also interesting to note that Porsche's "max effort" cars, the GT2, GT3, and Turbos, all run 160F stats from the factory.

I'm metric when it comes to oil and coolant temp. My car runs at 88 or 89C steady state. That's totally fine.

What I don't like is how hot it can get when stressed or in traffic.

Moreover, the thing the low temp stat is advertised as being preventative for is bore scoring on some of the larger M97 engines, which is supposedly a problem related to very high temps and hot spots.

But I am at a loss as to how it does this since at higher temps, there's no difference between the two stats.

GT2/GT3/Turbo all have very different engines (well, did until the Mezger was dropped fairly reently). There are lots of things they have that may or may not be a good idea for the M96/7 engines.

[JFP in PA]

Originally Posted by pothole

Moreover, the thing the low temp stat is advertised as being preventative for is bore scoring on some of the larger M97 engines, which is supposedly a problem related to very high temps and hot spots.

But I am at a loss as to how it does this since at higher temps, there's no difference between the two stats.

Easy, when the coolant in an M96/97 is running 210F (99C in your world), a commonly observed steady state driving temp when measured with accurate instrumentation (which the dash display is notoriously not); due to the rather intricate cooling system layout in these engine cases and cylinder heads, there are areas of the engine that are often 20 to 30 degrees F warmer than the observed coolant temp due to restricted coolant flow. This leads to prolonged alloy component distortion and is one of the principal reasons these engines are prone to both cylinder head cracking and cylinder wall problems. Throw in faster oil degradation and you have a potential issue..........

[pothole]

Incidentally, the standard stat for bombproof 90's BMW straight sixes is 88 degrees.

It's a complicated topic. I'm yet to be convinced that a low temp stat is unambiguously a good thing.

Probably the ideal would be a stat that opened at 86 degrees like the factory stat, but opened fully at that temp. But even then, It's not going to make much difference as muc car only runs a few degrees higher than that normally.

[pothole]

Originally Posted by JFP in PA

Easy, when the coolant in an M96/97 is running 210F (99C in your world), a commonly observed steady state driving temp when measured with accurate instrumentation (which the dash display is notoriously not); due to the rather intricate cooling system layout in these engine cases and cylinder heads, there are areas of the engine that are often 20 to 30 degrees F warmer than the observed coolant temp due to restricted coolant flow. This leads to prolonged alloy component distortion and is one of the principal reasons these engines are prone to both cylinder head cracking and cylinder wall problems.

I read my temps from the AC panel hack, not the temp gauge. It's not quite as accurate as direct from OBD, but I doubt it's anything like 10 degrees out (which is a lot in C). I have connected via OBD once and there was only a couple of degrees difference.

I do not think these cars run at 99C in normal driving. The stat would be wide open and the engine would then cool down. In steady state driving with good air flow, the stat is going to be partially open, not wide open.

Like I said, mine runs at 88 to 89 when cruising, which makes perfect sense given the stat starts opening at 86.

[JFP in PA]

Originally Posted by pothole

Incidentally, the standard stat for bombproof 90's BMW straight sixes is 88 degrees.

It's a complicated topic. I'm yet to be convinced that a low temp stat is unambiguously a good thing.

Probably the ideal would be a stat that opened at 86 degrees like the factory stat, but opened fully at that temp. But even then, It's not going to make much difference as muc car only runs a few degrees higher than that normally.

Comparing the impact of coolant temperatures over time between an M96/97 to another make is an "apples to oranges" concept; their are entirely different animals due to the coolant system flow characteristics. The M96/97 has several widely known and accepted weaknesses, poor coolant flow in some areas is just one, but one that can be addressed by simply cooling the engine down somewhat.

[pothole]

Perhaps. But I'm not convinced. I have no idea where you get the idea that these engines run at 99 degrees steady state for instance.

The BMW comparison was not meant to be definitive and is no more or less relevant than your mention of the Mezger engine in GT2/3 and Turbo.

But apparently it's OK for you to draw comparison with completely different engines, just not for me!

[JFP in PA]

Originally Posted by pothole

I read my temps from the AC panel hack, not the temp gauge. It's not quite as accurate as direct from OBD, but I doubt it's anything like 10 degrees out (which is a lot in C). I have connected via OBD once and there was only a couple of degrees difference.

I do not think these cars run at 99C in normal driving. The stat would be wide open and the engine would then cool down. In steady state driving with good air flow, the stat is going to be partially open, not wide open.

Like I said, mine runs at 88 to 89 when cruising, which makes perfect sense given the stat starts opening at 86.

I am not a fan of the AC display hack and many of them are not accurate either. We prefer either actual quality instruments (after market gauges) or the use of the PIWIS or Durametric system, both of which have proven to better agree with aftermarket instrumentation setups.

We have clocked literally dozens of customer cars running well north of 205 F, even in relatively cool ambient air temperatures. Problem is that the OEM stat starts to open at 186F, but does not fully open until much higher temps are reached. You can verify this for your self by suspending an OEM stat in a beaker of water and monitoring when it starts to open, and when it is fully open.

[pothole]

The single argument I have heard in favour of the low temp stat that makes some sense is one you have not mentioned at all.

It relates to speed of reaction and the fact that the stat is place at the inlet side on the engine. IE the stat sits on the engine where the coolant from the rads comes in, rather than where the coolant from the engine leaves for the rads.

In this scenario, you can imagine how it would take quite a time for hot coolant to make it's way round.

I am not sure if this is true (the stat placement), but if it is, it does rather argue for a lower temp and faster opening stat.

[JFP in PA]

If you have access to the Bentley manual for the car, I believe there is a simplified flow diagram in it that shows the stat on the return from the radiators to the engine.

I tend to focus more on why these engines are so hard on oil, and what can be done to reduce that, as well as limiting as much as possible the thermally induced stresses put on the alloy components by a system with known hot spots and flawed coolant flow problems. Lowering the coolant temp appears to help both, as does adding the larger "S" oil cooler to base engine cars.

[mikesz]

I changed my thermostat to a low temp version when I changed out the water pump and replaced system with fresh coolant. I also added an S center radiator to my 99 base 2.5. Because I felt like it!

[MikeDelta]

Has someone installed with the lower temp thermostat a manual switch for manually switching on the radiator fans

Sent from my IRON using Tapatalk

[MikeDelta]

Has someone installed together with the lower temp. thermostat also a switch for manually switching on the radiator fans?

Sent from my IRON using Tapatalk

[mikesz]

I am pretty sure I saw a post on one of the forums someone did it but it wasn't something I wanted to do so didn't follow it.