Thermostat question

I have read that when you replace your water pump you should do the thermostat as well. Is this one of those "while your in there" situations? How can I actually tell if my thermostat needs to be replaced? Recently the car has been running slightly hotter than I remember. I plan on giving the rads a good clean to see if this helps at all. Any suggestions?

Yes, it is one of those "while you are in there" jobs. It is right next to the pump and you will have to drain at least a portion of the coolant for both anyway. And don't ask how you can tell if you need a new stat. If you are replacing the pump, and your car is running hot, and the stat has never been replaced, and your car is now 13 years old.....you have answered your own question. I suggest getting the lower temp stat (160) that is offered by many vendors and try to determine why your car is running hotter. Is the coolant original? are the low & high speed fans working? Are the radiators free of debris? Start there. Good luck.

Quotes source post: 9888135

My auto mechanic friends always taught me to when replacing the water pump to replace the T-stat at the same time. I was also taught to before installing the new T-stat to drop it along with the old one in a pan of water on the stove and bring the water temp up and using a thermometer note at what temp the T-stats opened and to confirm at least the new one was fully open at some point. You want to avoid the small risk of installing a mis-marked or bad new T-stat. The only times my cars have run a bit hotter than usual -- based on observing the coolant temp gage -- has been due to a non-functioning radiator fan. The change was not dramatic but it was real. Check the fans to be sure they not only come on when the A/C is turned on but they come on when the coolant temp rises to the trigger point. Always keep the radiator ducts clean. Do not install a low temp T-stat. My apologies to those that expouse this course of action, I'm sorry, but this is just some lame assed shade tree mechanic car hack. A low temp T-stat simply results in a slower to warm up engine with resulting increase in wear. These engines -- and the oil they are supposed to run -- are designed (and the oil spec'd) from the ground up to operate just fine with the stock T-stat and the car's cooling system and the temperature ranges these result in. (For example: I have observed for instance my 02 Boxster operating with a coolant temp of 226F (it never got any higher even when a year or so ago I tried to get it higher) form some -- in one case for hours in the very high AZ summer time heat -- without any harm. I might note the engine has experienced this elevated temperature operation several tiems over the last 260K miles and has not suffered one whit from it.) The only overheating issues these cars have is in the over active minds of their owners though of course this assumes the cooling system is in tip top shape/condition at all times. Which is often, I'm sad to state, not the case. The only time an otherwise perfectly functioning cooling system could use some help (just to repeat mysef: a low temp T-stat is not help but harm) is if you have increased through mods the engine's output or compromised the cooling system's operation by ill-advised mods to the body and thus changed the aerodynamics and cooling efficiency/performance of the stock car. If you believe you car requires more cooling install a 3rd radiator like the factory does to increase the car's cooling capacity some. I note my Turbo has a 3rd radatior and even when making its full 420hp at over <static> on a deserted road out in the great southwest in triple digit heat suffered not one bit from the effort. I never even bothered to turn off the A/C. Sincerely, Macster.

Thanks pointing me in the right direction. Hopefully this weekend I can get to cleaning the rads and check the fans. Haven't decided whether or not to install low temp stat.

You know everybody thinks the Porsche engineers always do things for the right reason. Porsche engineers make compromises and mistakes. The reason for the high temp thermostat is to make the engines run hot and therefore put out less polution. The Porsche engineers, if they had there way would run a lower temp thermostat. It is a fact these M96 engines run hot, anything you can do to lower the operating temperature is a good idea and will increase longevity. Check out LN engineerings explanation for the advantages of the low temp thermostat. Macster is a star and he knows these cars very well. His advise is usually very good. But in this case as an aerospace engineer and experience with thermodynamics I disagree with him.

Quotes source post: 9892223

Just curious...how do you know this?

There is an optimum temperature for generating horsepower, and another for the least amount of emmisions, they are not the same. Higher temps at a certain point in internal combustion engines generate less smog, and less horsepower and more wear. These are established facts. Search the net to find a multitude of papers written on the subject. Ask those who race, they have experienced this fact and will tell you so. If you lower the temp of your 996 to the optimum level it will generate more horsepower, this is proven through testing on the Dyno. Do you think Porsche engineers would purposly leave horsepower on the table without a good reason? That is how I know.

Quotes source post: 9892389

And let's not forget what else higher temps generate in these engines: Cracked heads & cracked cylinder liners. Bottom line it the low temp stat from LN.......works. It warms up just like any other stat and opens gradually at 160 and is fully open well before the 180 factory stat is fully open. There have been countless analyses of the need for the lower temp stat from many reputable sources. But, to each his own. To call it a "lamed *** shade tree mechanic car hack" just proves ignorance.

Quotes source post: 9892389

I just thought you actually KNEW a Porsche engineer. I was gonna have you ask him why he put my cup holder in front of my air vent!

will be doing WP/T-stat/reservoir soon and came across this thread while researching. Saw a Porsche part listed by Pelican: 996-106-013-59-M902: Water Thermostat, Low Temperature (begins opening at 160 deg F) with Cover and Gasket, 996 Carrera 2/4 (1999-04) Safe to say that PORSCHE does/did recognize the benefit of a low-temp t-stat?

Quotes source post: 10012650

That at some point a 160F t-stat was made and is now for sale on some web site that sells parts based on simply having them in stock and selling them to who ever asks and is willing to pay does not in my mind mean that Porsche does now or did even then recognize any benefit of a low temp t-stat. There are various sites that sell items that manufacturers (car parts, electronics, etc) no long stock because they have been superceded by newer parts. Some of these parts are of questionable quality having been rejected due to manufacturing defects; not all are bad but enough to reject the whole lot and these can end up offered for sale to the unsuspecting. Also, it is possible that the t-stat maker unloaded those t-stats because Porsche rejected them because it found 160F t-stats unsuitable. But of course to those that think the Porsche engines only need to run cold in order to last a long time will flock to those colder t-stats like crazy. The 996 engine fountain of youth of du jour.

Quotes source post: 10012650

This part is not available from Porsche for 996's. However 996 Turbos come with 160 T-stat. (doesn't fit non-turbo)

Thanks both to Macster and Byprodriver for your replies.

I would sure hope Pelican would never sell rejected parts. While I also agree with Macster's conservative advice most of the time, this is not one of them. There was another RLer that always went a bit overboard on how low temp T-stats did nothing, (the opposite of what Macster is saying) and that if anything, a lower temp switch for the rad fans or a manual switch hack were better (in effect, doing what Macster says is bad, lowering the coolant of the temp below the original design point). His point was that both T-stats would be wide open at normal operating temps ( the temp the T-state sees exceeding 210�F, according to him) anyway, so how can it help? The third rad or earlier fans was the only solution. I agree with Cornbread here, it is Thermo 101 that the larger temperature differential will always generate more power, and that the temperature chosen would be more for emissions, which would counter HP or longevity. Porsche would never offer for sale an approved lower temp T-stat if the car could not make emmisions guarantees with it installed. Virtually all the respected indie engine rebuilders, here and in Europe, recommend the lower temp T-stat. There are quite a few in depth failure analysis and studies by them, in a search for failure prevention. No one comes up with a low temp T-stat, then looks to find a reason to install it. That makes no sense at all. As stated, the Turbo already has a lower one, as does the 997 IIRC, and 991. The difference in warm up time has been shown to be insignificant. Much, much, less than the difference in warming up your car after it's been sitting out all night in below 0 temps, vs sitting out in 70 degree temps, so the whole "longer to warm up, means more wear" argument is nonsense, I'm sorry. As Cornbread said, Dyno tests show a modest increase in HP (something just under 5HP), so it is apparant that there IS indeed some thermodynamic benefit from the 160�F T-stat, unlike what the other RLer espoused, that they are both full open and there is no flow difference. Apparantly, the 180�F T-stat is not full open at normal operating conditions. It has also been stated that the temp indicated on the dash is after the rads, so the actual hottest coolant temp is much higher, perhaps even 40� more. That would put the coolant too close to the boiling point for me, also a mechanical engineer, simply from the headroom aspect. If everything always works as it should, then the 180� T-stat is likely just fine, as stated. But we know that (and by Macsters own admission) that is not always the case, and the 996 DOES have more heat related engine issues due to localized hot spots, than the average engine, and anything that can increase coolant flow to those areas is always a good thing, especially on the MKII engines where they went with symmetrical cooling passage gaskets vs balanced asymmetrical gaskets. Others that have already installed the 160�F unit on NA M96 engines state that the temp gauge shows little difference, perhaps a few degrees AVERAGE as indicated, so what we have is a thermodynamic benefit indicating more flow and cooling, benefitting a few (?) much hotter spots due to increased flow, (but since the average temp is not a lot lower, not driving the engine temp as whole too low at all), which increases the coolant top temp headroom a bit, gives a little extra HP, and has the likelihood of preventing a borderline cooling issue from causing real harm. Where is the harm at all in this?

Another factor to consider is where the thermostat and coolant temperature sensor are located on the M96/M97 engines. The t-stat is located on the return side of the coolant loop and the temp sensor is located where the coolant flows through the oil pump housing after exiting the water pump, prior to circulating through the engine. What this means is that the t-stat and temp sensor are sensing the temp of the coolant after it has been through the radiators, probably the lowest temp in the system. If the coolant is at 180 degrees to open the t-stat, then it is much hotter when it exits the engine to flow through the radiators. And if the temp sensor is showing 200+ degrees this means that the coolant coming out of the engine is much hotter than that.

Newbie and here to learn. With that being said, I am no stranger to high HP and forced induction cars. The only thing that a cooler thermostat will accomplish is take longer to get to the same temperature. After a certain period of time, both will reach the same temperature and maintain it. The only real way to lower temps consistently, is to increase radiator volume and upgrade cooling fans. Water wetter helps a bit.

Again, neither I nor Doug are "trying" to lower water temps! If you have experience with other high HP cars, then great, but where are their T-stats and indicator sensors located? Like you said, the most solid way to lower temps is to increase rad surface area, or increase airflow, OR increase coolant flow through the system. That was the only real point of my previous lengthy post. Hartech and others all are saying, that based on their measurements, which far exceed all our armchair posturing, that the existing T-stat impeds some flow at normal temps, and that by the time the T-stat can react to the increased temps to increase flow, too many hot spots have suffered. If you are doing a water pump anyway like I am, and you believe in replacing the T-stat as a wear item like I do, then the extra $70 is a no brainer, with no negative side effects and only possible positive ones. The extra warm up time is insignificant, and there is definitely a thermodynamic effect. It is totally misleading to say the lower temp stat does nothing. I have said that the average mixed coolant temp is about the same. Many that have put in the low temp one complained because the gauge showed little if any change! Good! But that does not alter the fact that the localized flow challenged locations are now benefiting from full flow at all times, instead of being choked back when the engine hits high revs and output and having to wait until the entire 6 gallon coolant system rises in temp to open the t-stat to where it should have been minutes ago.

Quotes source post: 10014999

AMEN!!!! +996!!!!!

Quotes source post: 10015308

I wasn't saying don't get one. I'm only saying that all it does is open sooner. A thermostat is a stat is a stat. Regardless what temp you decide to use, it would be silly to not replace it while you are there.

Quotes source post: 10014118

Might as well save your breath. Lower temp t-stat is the 996 engine savior in favor right now and no amount of intelligent counter point will change anyone's mind. My Boxster's coolant temp reaches 226F (but never any higher) under some extreme driving conditions in high ambient temps. The t-stat is marked "83" which is 181F. The darn thing is fully open and yet the coolant temp is quite a bit above that. What would be necessary to lower that upper temp? I might also add the times I have monitored coolant temp when moving down the road the coolant temp hovers around 186F so if vehicle speed is sufficently high this alone moves enough air through the radiators to keep the coolant temp quite low. Anyhow, what would lower this 226F peak temp? A t-stat that opens at even a lower temp that 181F? Hardly. More radiator capacity or more air flow through the existing radiators is the answer. Which is what Porsche does for its vehicles (Turbos and Tip/PDK equipped) which generate/produce higher heat loads. While my Boxster's coolant temp reaches 226F the Turbo's never gets anywhere near that hot and that is because is has 1) 3 radiators; 2) better aerodynamics to encourage more air flow through the radiators; 3) different electric radiator fan operation which has the fans on to move more air through the radiators when the car is not moving fast enough to accomplish this. But of course Porsche knows nothing about cars and must have selected a too high a t-stat by mistake and hit upon 3 radiators, more air flow from increased fan action, and better aerodynamics by accident. What it means to me this lower temp t-stat business is it is just one more thing to have to think about when buying a used car. Try to determine if one is installed and if so then walk away.