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