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Old 04-22-2009, 06:05 PM   #1
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Bad Thermostat?

I'm changing my coolant and I think I have a bad thermostat. I filled the coolant tank to the filler neck and ran the car until the thermostat should open like the Bentley manual says. The coolant temperature got to 90 degrees Celsius and the hose from the thermostat housing to the front of the car was still cold. Very little drop in the level of the coolant tank and no fans turned on.
This might also explain why the coolant temp gets to 108C when stuck in traffic.

Time to replace the thermostat?

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Old 04-22-2009, 07:02 PM   #2
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might be obvious, but did you close the bleed valve after the coolant change?
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Old 04-22-2009, 07:05 PM   #3
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what is the thought about the 160F thermostat from Raby's store? I have read that it is the best thing ever and have read that it will not make a difference. My temps stay at 198-202F when driving.
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Old 04-22-2009, 09:19 PM   #4
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Quote:
Originally Posted by jhandy
what is the thought about the 160F thermostat from Raby's store? I have read that it is the best thing ever and have read that it will not make a difference. My temps stay at 198-202F when driving.

For a car that's driven HARD, the 160 T'stat has some benefit. But it won't regulate the overall operating temp, the car will still run in the range you had before.

The 160 is just the temp where the T'stat opens and allows the coolant to flow fully through the system. Before this temp is reached, the coolant flows in a closed, or partially closed, circuit avoiding the radiators, to retain heat to warm the car up faster to operating temp.

The car will not temp spike as severely as with the oem 180 unit (a T'stat lags behind the actual temp). And, for a normal street car will take longer to fully warm because heat is being shed (by running to/from the radiators) sooner.

But all we're talking about here is the period from cold to fully warm, after that, the T'stat (whether 160, or 180) is fully open and will remain that way until the car is shut off and cools, because once warm and operating, it will not dip below 160 or 180 for the duration of the run.

But the cooling system is only responsible for about 20-30% of the overall cooling, or better, heat removal. The oil carries away about 50-60% of the heat (mostly from critical components) and the spark plugs and exhaust about 5-10% each.

For the Boxster, because of the oil-to-water heat exchanger (oil cooler), the coolant does have to carry away much of this heat too as opposed to a conventional oil cooler where the heat is released directly to atmosphere.

In TX or other southern climes, it's possibly beneficial. Or for a northern car which is only run in temperate weather. But for a northern car run year round, it may be a detriment because of the delay in getting it up to operating temp during cold weather.

My car is a northern car run only in warm weather, so when the time comes for me to replace, I'll look at the 160 unit and if it's cost competitive, will likely go with it. But if I ever started driving year-round, I'd revert back to the oem 180 unit.

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Old 04-23-2009, 04:55 AM   #5
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We ran the 160F low temp thermostat all winter in my Boxster with no ill effect as to warm-up. You receive the same amount of heat and just as fast as the stock 186F thermostat, even in sub zero weather.

If you're stuck in traffic or low speed operation, the coolant temp will creep up as with the stock thermostat until the fans go. Once in motion, the coolant temp will drop quickly. In the winter, it would stabilize at 172F. Last week with ambient air temp approaching 80F, it was hovering around 176F.

One of the main reasons to run the low temp t-stat is to lower the oil temperatures, which already run too hot for my liking.

As a side note, I had an owner of a GT3 call and want a low temp thermostat. I asked what he runs for coolant temps and he said it stabilizes at 176F in mid-70s ambient air temps, so it would appear Porsche already has a low temp t-stat standard in the gt3, gt2, and turbo. He also said his oil temps ran about 190F, showing an oil temp 10-15F above coolant temp, which I have observed before in cars with laminar flow oil to water coolers, like our cars have.
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Old 04-23-2009, 05:53 AM   #6
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Quote:
Originally Posted by cnavarro
We ran the 160F low temp thermostat all winter in my Boxster with no ill effect as to warm-up. You receive the same amount of heat and just as fast as the stock 186F thermostat, even in sub zero weather.

If you're stuck in traffic or low speed operation, the coolant temp will creep up as with the stock thermostat until the fans go. Once in motion, the coolant temp will drop quickly. In the winter, it would stabilize at 172F. Last week with ambient air temp approaching 80F, it was hovering around 176F.

One of the main reasons to run the low temp t-stat is to lower the oil temperatures, which already run too hot for my liking.

As a side note, I had an owner of a GT3 call and want a low temp thermostat. I asked what he runs for coolant temps and he said it stabilizes at 176F in mid-70s ambient air temps, so it would appear Porsche already has a low temp t-stat standard in the gt3, gt2, and turbo. He also said his oil temps ran about 190F, showing an oil temp 10-15F above coolant temp, which I have observed before in cars with laminar flow oil to water coolers, like our cars have.
Good info. Charles thanks!

I'm sometimes a little slow on the up-take, so let me ask some additional questions.

Essentially, the importance of what you are describing isn't the opening temperature of the T'stat, but the closing temp?

IIRC, pretty much all T'stats work the same way: a cylinder w/ a wax pellet on the engine side of the T'stat has a piston on it attached by a rod to the valve. When the heat from the engine heats the wax pellet, it expands (both from the heat and from the phase change of a solid to a liquid - liquids are more voluminous than a solid of equal mass), pushing the piston and opening the valve allowing coolant to now flow to the radiator. Different opening temps are achieved by differing wax compounds and/or return spring pressure.

But, once open, they're all the same.

What you're saying (if I read you correctly) is that the temperature sensitivity is such that even a 4 degree difference (180 vs your observed 176) is sufficient for the wax to start to contract and allow the return spring pressure to overcome the piston pressure and close (or partially close) the valve and reduce coolant flow to the radiators? Are they that sensitive?

And, if so, once closed and the temp rises 4 (back to 180), the valve reopens, and the process starts all over again. To me then, it seems that the 180 T'stat is just more cyclic than the 160 one.

But does that really significantly effect overall operating temp? And, if so, by how much - what is the avg. running temp using the 180 T'stat? And what does that temp difference affect adversely? I mean as far as I can see, we're only talking about 4 here.

If we're looking to decrease the overall operating temp as a goal, would it be more effective (albeit more costly) to increase the capacity of the system by adding say the center radiator on non-S cars? Or by taking the oil cooling out of the loop and routing the oil to a conventional oil-to-air cooler? TIA

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Old 04-23-2009, 08:20 AM   #7
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I, too, have wondered about this, and from what I can tell, if you want to get lower operating temps it would make sense to remove the oil cooling from being part of the coolant loop and use a traditional oil cooler. Although, doing so would likely increase warm up times from a cold start.
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Old 04-23-2009, 09:37 AM   #8
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Back to the original question...
Do I need a new thermostat?
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Old 04-23-2009, 03:34 PM   #9
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Quote:
Originally Posted by derb
Back to the original question...
Do I need a new thermostat?

Sorry for 'feeding' the hi-jack!

You might need a new T'stat, but unless you've had overheating issues before, it's more likely that there is still air in the system.

Do you have a tiptronic? The Bentley fails to mention the additional step needed for filling/bleeding the tip cars - pull fuse #B1 (tiptronic module), ignition OFF to disable the tiptronic coolant shut-off valve before bleeding procedure.

Many here reported having to bleed the car over several days driving to purge all the air from the system, manual or tip.

After 10 min. running time, the radiator feed hoses at the front of the car should be warm, maybe HOT so be careful.

If not, and you're positive that all the air has been purged, then yes, the T'stat can't be ruled out, but neither could a waterpump with a failed impeller. In either case, you should eventually get a coolant temp warning light.

You can remove the T'stat and perform the boiling water test, but since it's the same thing as replacing it (minus the expense of course), if you were thinking of that, my recommendation would be to just replace it.

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Old 04-24-2009, 06:52 AM   #10
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I guess i'm not understanding this either. Once the T-stat is open what difference would it make once the car is up to temp? It just opens sooner right during the warmup period?





Quote:
Originally Posted by cnavarro
We ran the 160F low temp thermostat all winter in my Boxster with no ill effect as to warm-up. You receive the same amount of heat and just as fast as the stock 186F thermostat, even in sub zero weather.

If you're stuck in traffic or low speed operation, the coolant temp will creep up as with the stock thermostat until the fans go. Once in motion, the coolant temp will drop quickly. In the winter, it would stabilize at 172F. Last week with ambient air temp approaching 80F, it was hovering around 176F.

One of the main reasons to run the low temp t-stat is to lower the oil temperatures, which already run too hot for my liking.

As a side note, I had an owner of a GT3 call and want a low temp thermostat. I asked what he runs for coolant temps and he said it stabilizes at 176F in mid-70s ambient air temps, so it would appear Porsche already has a low temp t-stat standard in the gt3, gt2, and turbo. He also said his oil temps ran about 190F, showing an oil temp 10-15F above coolant temp, which I have observed before in cars with laminar flow oil to water coolers, like our cars have.
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Old 05-04-2009, 08:41 AM   #11
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We are running one of LN Engineering's 160 stats in a customer's car (01 2.7 base but equipped with the "S" oil cooler) and have consistently noted 15-18 degree lower coolant temps when compared to the OEM 185 stat. We have observed lower operating temps both around town and on the open road. One thing you have to note is that the factory temp gage is neither linear nor accurate, so you have to observe the real temps via the OBD II port. And the difference is substantial; we noted that when the cooling fans came on, the dash gage said about 190, the OBD II port said over 210, and when running on the open road, the dash gage said just under 180 while the OBD II said more like 15 degrees lower........ The stat does appear to make a make a real difference in general operating temps, but unfortunately with the inaccuracy of the dash gage is is a little hard to observe.

Last edited by JFP in PA; 05-04-2009 at 08:48 AM.
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Old 05-04-2009, 09:17 AM   #12
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Quote:
Originally Posted by JFP in PA
We are running one of LN Engineering's 160 stats in a customer's car (01 2.7 base but equipped with the "S" oil cooler) and have consistently noted 15-18 degree lower coolant temps when compared to the OEM 185 stat. We have observed lower operating temps both around town and on the open road. One thing you have to note is that the factory temp gage is neither linear nor accurate, so you have to observe the real temps via the OBD II port. And the difference is substantial; we noted that when the cooling fans came on, the dash gage said about 190, the OBD II port said over 210, and when running on the open road, the dash gage said just under 180 while the OBD II said more like 15 degrees lower........ The stat does appear to make a make a real difference in general operating temps, but unfortunately with the inaccuracy of the dash gage is is a little hard to observe.
This testimonial parallels what we hear all the time concerning this product. It is also in line with the temperatures and results that I observed during the development of the product as I assisted LN Engineering.

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Old 05-04-2009, 06:06 PM   #13
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In the late 80's I used to build and race small block Chevrolet street/drag motors, and one of the "tricks" we had to keep things either cool or within a specific range was to drill a hole between 1/8 and 1/4 in the t-stat plate. This allowed some coolant flow before temps reached the opening point, and it allowed the t-stat to flow more coolant when open. As well, another argument was that it reduced pressures againt the water pump when the t-stat was closed, reducing pressure and wear on the seals and bearings.
Thoughts on this mod for the Boxster???

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Old 05-05-2009, 05:30 AM   #14
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We used to pull the t-stat out in the summer.



Quote:
Originally Posted by j.fro
In the late 80's I used to build and race small block Chevrolet street/drag motors, and one of the "tricks" we had to keep things either cool or within a specific range was to drill a hole between 1/8 and 1/4 in the t-stat plate. This allowed some coolant flow before temps reached the opening point, and it allowed the t-stat to flow more coolant when open. As well, another argument was that it reduced pressures againt the water pump when the t-stat was closed, reducing pressure and wear on the seals and bearings.
Thoughts on this mod for the Boxster???
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Old 05-05-2009, 05:43 AM   #15
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The M96 has some "Bypass" built right in to the engine.. No need to alter the T stat.
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Old 05-05-2009, 05:52 AM   #16
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What am I missing here man?
A lower temp t-stat opens sooner (coolant a bit cooler than full temp) Once warmed up though, the t-stat would stay open no matter how early it opened no?

The only thing I can thing of is that after the T-stat opens it will close once the coolant temps drop below it's rating. So it's always opening/closing?

Open = more cooling. So a 160 will actually stay open longer than a 185 assuming the coolant temp can cool down below 185 degrees.

The idiot gauge calibration isn't good enough to show a drop of 20 degrees?





Quote:
Originally Posted by JFP in PA
We are running one of LN Engineering's 160 stats in a customer's car (01 2.7 base but equipped with the "S" oil cooler) and have consistently noted 15-18 degree lower coolant temps when compared to the OEM 185 stat. We have observed lower operating temps both around town and on the open road. One thing you have to note is that the factory temp gage is neither linear nor accurate, so you have to observe the real temps via the OBD II port. And the difference is substantial; we noted that when the cooling fans came on, the dash gage said about 190, the OBD II port said over 210, and when running on the open road, the dash gage said just under 180 while the OBD II said more like 15 degrees lower........ The stat does appear to make a make a real difference in general operating temps, but unfortunately with the inaccuracy of the dash gage is is a little hard to observe.
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Old 05-05-2009, 07:21 AM   #17
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Quote:
Originally Posted by Sputter
What am I missing here man?
A lower temp t-stat opens sooner (coolant a bit cooler than full temp) Once warmed up though, the t-stat would stay open no matter how early it opened no?

You are correct in your assumption that once at rated temp, the stat stays fully open, unless the ambient air is so cold it begins to pull too much heat out of the system. Think of the stat as controlling the minimum temp of the coolant (which it does in colder outside temps). Because it is fully open at a lower temp (160 degrees), the engine has a reserve of lower temp coolant in full circulation to absorb heat being put out by the engine and oil and carry to the radiators earlier than with a higher temp rated stat.

The only thing I can thing of is that after the T-stat opens it will close once the coolant temps drop below it's rating. So it's always opening/closing?

It can cycle, but usually only at relatively cold ambient temps. On a 70 degree day, once it opens, it usually stays open.

Open = more cooling. So a 160 will actually stay open longer than a 185 assuming the coolant temp can cool down below 185 degrees.

Correct. On a 72-75 degree day, open road cruising with a 160 stat, the coolant will actually drop well below 180 degrees (in testing, we saw 167-170 via the OBD II port).

The idiot gauge calibration isn't good enough to show a drop of 20 degrees?

The temp gauges in Porsches have been a sore point for years and across all models; they are notoriously inaccurate and non linear.

..............
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Old 05-05-2009, 10:24 AM   #18
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Thanks man, I get it now.



Jim



Quote:
Originally Posted by JFP in PA
..............
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Old 05-05-2009, 12:08 PM   #19
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Thanks man, I get it now.



Jim
Anytime......................
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Old 05-05-2009, 02:09 PM   #20
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Quote:
Originally Posted by Jake Raby
The M96 has some "Bypass" built right in to the engine.. No need to alter the T stat.
Does the heater core always flow? If so, then that's bypass also.

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