Temperature management on 996 Mk.1

Sounds like a beaten-to-death subject however I have been having difficulty finding a cohesive overview. I would like to understand how the temperature management works on my 996.1 and what is considered normal behaviour when the cooling system is working optimally, as it was designed. Next question is what kind of modifications are available and what effect those have. This is what I have derived, which might or might not be correct: - standard thermostat starts to open at 187F (86C) and is fully open at 210F (99C) (= info from site Pelican parts) - a LN low temp thermostat starts to open at 160F (71C) and is fully open at 180F (82C) - car has a right and left radiator on which is bolted as well the AC condensor (l/r) - right fan comes in at 201F (94C), high setting - left fan comes in at 225F (107C), high setting - with aircon on l/r fan also come at a low setting - read out of temperature on dashboard (analog) is the engine temperature, probably close to thermostat and it reads the actual temperature. Thermostat is situated at entry of engine block cooling circuit so actually represents the lowest temperature found in the cooling circuit - you can also read out the temperature digitally on the display of the airco unit What I observed is that even at moderate outside temperatures (70F) after normal cruising at highway when entering the city with stop & go traffic the displayed temperature slowly goes up from 195 +/-5 to 225 when the left high fan also kicks in and then it slowly pushes down the temperature. To me, that does not seem very normal so I am considering either to swap to new the waterpump and thermostat (which I suspect are stock, this is a Jan 1998 car), I could then consider to insert a low temp thermostat (given feedback from ao mr. Raby indicates this makes a lot of sense). There is also a local shop here that claims to do an upgrade to the car that makes temperature management rock solid by installing a high volume waterpump (does that exist?), move thermostat to engine block exit iso entry and reprogram the fans so they kick in earlier. To complete the picture I also understood that on Mk2 cars things work approximately the same but Porsche "fixed" the temperature gauge so it does not read higher then 190F (0 on the 180) even if the actual temperature is higher. Only when it goes to red zone, it flips to the right. OK gentlemen, to the startline and go! Looking forward to your observations.

just my 2 cents, but I live in the southern US and I have to really lay on the car and then sit in traffic to get above 215-220. Thats when its 90-95 degrees outside and humid as hell.

I thought I once read that the 997 WP fits and is more efficient (I may be wrong) combined with the LTT you should be fine. Also reprogramming the fans would help too. Start with the easy stuff and see if it helps... Are you all tuned up with fresh plug/coil packs etc?

Also third radiator - some cars (tiptronics?) have it, some don't (probably yours). Been done to death on here. FWIW I had a third rad and low temp thermostat (and new water pump) done at the end of last year, very happy with the result.

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Thx. How would plugs/coil packs impact temperature management? Or more general question? After addressing heat mgt my next target would be chain tensioners (car has run 85k miles sofar). Volkert

Just cleaning the radiators/condensers (Search) and relocating the temp sensor for the Purge Fan helps. Cost is zero.

Radiators/condensors have been cleaned. Will check on purge fan. Any feedback on the mentioned temperatures? Are these correct? Volkert

The biggest benefit an early car cam see is a 3rd radiator, and use the updated CSF unit. When I test early cars I am seldom happy with the coolant temps that we see today. The radiators are getting older and seeing some corrosion internally, reducing the thermal exchange capability of the unit. The biggest issue I see comes from aftermarket bumpers with the wrong type of air inlets, and the proper shrouding to direct all the airflow through all of the radiator.. They stack all the air in at the outboard corners of the radiator, and only the back 1/3 of the radiator sees the proper air flow. I have been developing an arrangement to help with this, and it has proven to help.

I look forward to this new arrangement!

In the past few years I noticed that lots of cars that came here with intermixed oil and coolant, from cracked heads, and had aftermarket bumpers fitted. Some of the worst had the huge turbo inlets, which people often perceive with "bigger being better". When I put the cars back together, they also tend to run hotter than normal again, and we have to work to address the cooling arrangement issues t remedy this- else our engine will fail, too. I know exactly how hot these cars should run, and how the gauge should behave when driving my 52 mile test loop at different ambient temps.

OP, pretty much your post is accurrate. My car gets to 104C before the high speed fans turn on and up to 107C before it starts to cool down again to 104C. Only high speed driving gets the temps below that for me when ambient temps outside are high (70-85F). In the winter or below 50F outside, high speed driving has my temps sitting between 89-93C. Based on all this, including Hartech research, it makes sense to get these temps down rom where they are today. Cleaning the rads, moving the sensors, and doing a low temp t-stat are probably the best bang/buck. A 3rd radiator would be better. Normally, 107C by itself isn't going to cause a problem if the car is just sitting in traffic, although I still think 107C is too hot. But at that temp, if someone were to open the throttle and put the hammer down, we now have a sudden and rapid increase in localized heat that has to exit the engine and make its way back to the front of the car to be cooled before it goes back to the engine to cool the engine. And Coolant coming into the engine might not be that cool because air wasn't moving past the radiators to cool it down fast enough. Therefore, internal temps could very well be higher than 104-107C, and if oil temps are generally 10-20F higher than Coolant, we could start to see very low viscosities near the hottest parts of the engine, which can lead to a breakdown of the film layer, resulting in metal to metal contact. Moral of the story - low temp t-stat and whatever else you want to do to get the temps down should increase the life of the engine in hot weather. And don't worry about winter driving not being hot enough to vapor off any accumulated water as long as you change you Oil every year and don't take many short trips.

No aftermarket no-nothing on this baby. I like to keep her stock but with refinements internally. I have read in some threads as well that after waterpump/LTT replacement still temps were too high and only solution was to replace the radiators themselves as well. What are some thoughts on moving the thermostat to the outlet (so it acts quicker on added load to the engine)?

Some thoughts on mods for the cooling system. Actually my Indy has done them. - relocate the (low temp) thermostat at the exit of the engine: quicker response to high temperature conditions. - water pump with more capacity and modified with slightly smaller pulley: especially at idle and slow speed significantly more water is moved compared to stock - reprogram the ECU to switch on the radiator fans at a lower threshold temperature. Relocate temperature Sensor to a hotter zone.

But.... What happens when the response time is too fast? The cooling systems of these cars don;t need that much "help". But at high speed the pump cavitates. Been there, done that. These two things can be done, again, the CLT being moved has caveats with warm up times, sensitivity, and etc. The stock sensor is in a poor location, but a strategic location.

Any downsides to running a 3rd radiator? Don't have any problems with the cooling system but we do get hot summers here although winter is cool but not freezing. I'd like to have the 3rd rad for piece of mind and it looks awesome and better than the plastic block off section (might be more of a 6speed mod comment haha) Now that its getting colder my Mk2 C2 temp gauge is at the start of the 0 at op. temp (my gauge goes 0 - 80 - 120).

Sigh,,, 1. Remove rads. Clean them with medium pressure nozzle from back to front. Leave the condensers in, and clean them from back to front as well. Also use compressed air from back to front. 2. I ran a weak solution of pure water and muriatic acid through the rads to remove some scale. I think it was 15% and I left it in for about 20 minutes. You will see it vapor while it's descaling. Don't breath the vapor. Not recommended unless you really know what you are doing. 3. Add the 3rd rad. Either buy the whole kit from Roger at 928sRUS, or buy the rad from rockauto.com, and the hoses brackets from Pelican like I did. 4. Install a low temp t-stat. 5. Install new standard water pump. 6. Flush entire cooling system and fill with pure water and sufficient coolant. 7. Pressure test for 1 hour. 8. Drive the car. Your temps will run just to the left of the tick mark on the temp gauge except under worst case, where it will go to the right of the tick, or just about the '0' on the '180' under extreme conditions. There is no downside to adding the 3rd rad. It's on all tip cars, should be on manual cars in hot climates. Will not only lower your driving temps, it will bring up your hot oil pressure, and I've noticed a better fuel economy(not much), and also the AC will run better, and so far my high temp fan has never, ever come on. Not even in 98F temps in stop-n-go driving with AC on high.

Thanks for the write up Docmirror, that sounds very sensible. And thanks to all RL contributing, very helpful! Volkert

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I understand that the 997 wp has a metal impeller-probably lends itself to better efficiency. Porblem is that if the bearing goes out it eats up the casing, making it a great boat anchor, as that's not repairable.

If you order a WP for the 996 you will get no matter what the 997 WP as the 996 part is discontinued and succeeded by the 997 version.

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For what it's worth I just bought the water pump kit from Renn Part and it had a 996 part number stamped on it. https://rennpart.com/product/water-p...placement-kit/

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I understood the Porsche pumps are composite, not metal. http://www.pelicanparts.com/catalog/..._pg1.htm#item0

Ok maybe it gets a 996 number? Can someone comment on this? My previous statement about the 996 vs 997 waterpump was based on what I was told by a reputable source saying that the 996 waterpump you order nowadays is in fact the same as the 997.

I'd like to chime in. I live in San Jose, CA (Silicon Valley) and it can get hot and it seems that our traffic jams have increased over the years. In short, depending on the time you leave work, you can get into stop and go traffic. I recently purchased a 1999 C2 and instantly the temperature has bothered me. It especially did so driving it to SoCal for the Porsche meet at Fontana Raceway. The car got hot, no warning lights, however. Coming from a Corvette C6, which I could beat on all day and the temperature was well contained, the 996 temperature has been shocking to me. After that trip, I decided to install a 160 thermostat hoping to remedy the problem slightly. To my surprise, the temperature is only slightly cooler (picture attached). Based on my Corvette, I single out the ill-engagement of the fans to bring down the temperature. Thus, I am considering the "fan mod" hack, which I think is pathetic in itself that such a prestige name has these issues.

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Start with the simple things first and work down the list: - clean out your radiators - check your fans with a durametric it possible - coolant flush - make sure there are no pockets of air in the system Do you have an aftermarket bumper or do you have the correct air dams/guides for the bumper you have? If you dont that can cause heat issues.

Makes total sense. Once the thermostat is fully open, there will be no difference with a standard thermostat. I see very similar behaviour on my car. I just want to understand if the car is up to spec. Therefore clean radiators/check functionality of cooling fans/replace waterpump/thermostat. Last resort replace l/r radiators. My guess is only by adding cooling capacity (central radiator) as per Docmirror you solve the temperature swings on a Mk.1. Otherwise (with all checks/repairs done on above items your car is running in designed spec. This week I will have done the check on functionality of fans/replace waterpump + add LTT. Will report back on progress then.

If you dont have coolant age records or know what type it is you're better off flushing it and replacing it to see if that helps. ​​​​​

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I agree, but have you seen how expensive the Coolant is? And it's 6 gallons!

I think we might all have just been lulled to sleep by modern cars that have fake temperature gauges that sit exactly in the middle all the time. The coolant temperature changes quite a bit, but manufacturers have gotten tired of complaints like this, so they just make their gauge sit exactly in the middle unless the engine is extremely cold or hot. On a car with a more "real" gauge, it's totally normal for the needle to wander up and down a bit with driving conditions. It is not indicative of a problem. If your radiators are clean and the gauge stays away from the extreme ends of the scale, there's nothing to worry about.

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I sure do! I've replaced it twice in the last 3 years. New water pump was the first, new coolant reservoir was the second! I actually paid attention to the needle today crept up into the end of the "0" when I wasn't moving then when I was it would go back down to the end of the "8". My car's gauge is in celcious like yours should be but isn't :-p

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Actually it's only 3 gallons of coolant (Porsche pink stuff @$50/gal) and 3 gallons of distilled water (about $5-$6.00). Yeah it's expensive, but it's a Porsche we're talking about... So $150 for a DIY coolant flush once every 3 years or so... Not too bad in my book.

Went to the lower temp thermostat, third radiator and replaced the water pump, no problem with high temps. The last couple of days it has been 90 plus extreme humidity no issues. Worth the money.

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Pretty much this. it is normal for the true temp to wonder from say 190-220.

Very interesting thread, but I have a quick question. I'm still newer to the car, perhaps I haven't researched enough, but how I can tell if the radiator fans are coming on while driving? It seems on other cars I can hear them, but have never heard the fans on the 996 (Mk.2). Thanks.

My 1999 club racing 996.1 (SP996) overheated last year at NJMP (ambient temp 95 F). Cleaned the crap from the front of the radiators, fixed a bad L temp sensor, then installed a third radiator, new water pump and low temp thermostat. Using distilled water and water wetter. Also added the GT3 bumper with factory ducting to each radiator and put in a simple switch to manually activate both front fans. At full race speeds last weekend (WGI) the car ran a steady 190-195 degrees, though ambient temperatures were pretty cool - maybe 75 F. I run the fans manually when under yellow, staging or in the pits and it stays around 180 F. Next winter I hope to fabricate some baffles to improve flow through the side radiators. Here's the manual radiator fan control hack: https://rennlist.com/forums/996-foru...tment-fan.html

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True

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Thank you for the input. 1) I have flushed the system twice, once because I a leaky hose and second when the t-stat was installed. 2) Radiators have been brushed cleaned and blown with compressed air. 3) I assume my indy-shop checked for pockets. 4) Car is all factory, no after market bumpers 5) I really don't want to ghetto rig the car with the "fan mod" and a switch. Question: Will the fans engage with the A/C on, even with bad resistors? Other solution : https://www.vividracing.com/catalog/...150757633.html

For what its worth, my 99 will have the needle go from between the 8 and 0 of "180" (194 on my obd reader, 92c on the dash display) and go to where the needle is between the 0 and unmarked line (seems to be 220F according to my obd reader, 112c on the dash display). In low to mid 90's I have not been able to get the temp above the unmarked line. It is a bit disconcerting how much the 996 seems to rely on its fans to maintain its cool. I proactively replaced the fan relays and have cleaned the rads, replaced WP, and OEM thermostat, and updated the cap to the 04 rev. Running the Porsche coolant at 50/50.

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For this reason, the folks that are still running these higher temps, even after putting in all these tweaks, flushes, and mods, the simple fact is, many of these 996s still run hotter than we'd like. 112C (233F) is pretty warm for Coolant if you ask me. Mine has only gotten to 107C. Not sure what cooling system pressure is needed to keep water from boiling at these temps.

The previous owner had the center radiator installed along with all of the aero/aero II parts. I de-gunked the radiators prior to this trip, but no other cooling system maintenance other than verifying coolant levels haven't changed and no visible fluid hanky-panky (oil in the coolant/coolant out the tailpipe kind of hanky-panky). I did not datalog this trip, but I have a decent idea of how my gauge tracks acutalish data. The temp was nominal, right in the sweet spot of warmed up but not hot (again, by my decidedly imprecise calibration), even when we were driving at low speeds (35MPH) in 90-100 degree F ambient temps with the AC on after some higher-speed pulls. I was pleasantly surprised that NOBODY puked up any coolant, but most of the cars present live in the desert full-time and were probably better prepared than my decidedly half-a$$ed efforts. But at least I put the spare in the frunk, right? *sigh*

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I did all this with the exception of a new water-pump and a 160 thermostat. On the highway, with a 169 t-stat the temperature stays at the 180 line regardless of how hard I drive it. In city traffic, I can baby it and watch the temperature climb rapidly. Again, I am pointing fingers at the fans and thier engagement point. Has anyone tried CSF aluminum radiators? At roughly $1,000 I am ify about it. Thank you all for taking the time to post real life experiences with the heat issues.

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Certainly a factor. The cooling fans in my car don't even come on until the temp goes to 97C. That's the low-speed fans. The high speed fans come on at 102C (215.6F), while the thermostat is fully open at 210F. So if you think about it, the car won't even be at full cooling mode until 215F and above. So these cars run hot by design. My sisters 135i BMW did the same thing. Plenty of forum posts on that car too if I recall.

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It's interesting, the highest coolant temp I have recorded on the 996 is 210 F, but my Mini hits 221 F on a regular day.

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So once you are sure the waterpump is OK, radiators are cleaned and the fans are running as they should the next suspect are the radiators themselves. I have seen other reports that only when changing them the cooling capacity was back to where it should be. When changing them it makes sense if you are willing to spend the extra $$ to go for the CSF radiators. I observed the high fan kicked in at 107C, not 102C. My car is currently having the fan-check + install of new waterpump and LTT. Got a call that the left fan did not kick in at low speed (it did do this at 107C at high speed) so this might explain why I was seeing it go all the way up to 107C).

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Remember the 996 measures and regulates cooling water temperature when entering the engine while typical is that this is done when exiting the engine. So your Mini might run cooler then your Porsche...

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Good idea. I suspect that folks' fan and sensors might not be operating 100%. My 18-yr-old car, I suspect, doesn't kick in the low-speed fans unless the AC is on, indicating that somethings broken. I have yet to buy a Durametric, but looking for one.

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True, and what's funny to me is that if Porsche decided to put an oil temp gauge on the 996 like they did on the 997 and the older air-cooled cars, we would be fussing over oil temps instead of water temps, LOL. At the end of the day, Porsche might consider a track-car optional component that can be installed so that Porsche owners can control their car's oil and water temps. I propose a variable t-stat setting, along with overrides that allow folks to choose temperature set points for sensors and for fans. That way, Porsche street cars will still pass emissions and have good mileage, but fanatics (read: us) can control temps with an app to make us sleep better at night, even if sleeping better is the only benefit. To me, it could be like the variable **** intermittent windshield wiper control that lets me constantly adjust, to a finite degree, exactly how much delay I want for my wipers. As ridiculous as this level of control might appear to A 'normal' person, I love it.

Keeping everything clean and free from debris will go along way for helping keep things cool, you would be surprised what a few leafs could have on impact of cooling

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FYI, I have one and it is an enthusiast license, but I've plugged it into about 4 or 5 cars and it doesn't have even one VIN registered, so you are welcome to come over and plug in.

Yeah, my counter seems to be busted too - probably a symptom of the software not exactly being current not being able to write somewhere the more modern OSes now regulate.

So update: when checking the functionality of the fans it was clear the driver side fan did not come in at low fan speed, only high fan speed (at 107C). This in the end was a none-functioning solenoid (one dislocated pin). Since we were addressing cooling I had the waterpump replaced (the one coming out after 19 years was still perfect) and the thermostat by a low temp thermostat (Wahler 71C/160F). Also coolant flush (of course). Now driving at moderate temperatures engine temperature is at 82C and when getting into the city goes up a few degrees but comfortably below 90C. Not like before that it went all the way to 107C before the fans kicked in at high speed. So massive improvement, very happy.

Had a nice bumper to bumper drive over Coldwater Canyon in LA...outside temp was between 93 and 96F. Had the top down, no ac on. (The tip has and additional radiator and a fan goes on automatically at start up if the ac is on.) The engine coolant temp needle moved to the far end of the 0 in 180...and then drifted back to the middle of it. When I stopped the car to shop, no fans were running nor came on. The engine bay fan never came on. When I got on some open road and the air was flowing, the temp moved to the left side of the 0. All of this has been normal for the year and a half I've owned the car. If I was moving to Palm Springs or Pheonix or Texas I would go for the low temp thermostat but in Los Angeles, I don't feel it is necessary.

Probably the 3rd radiator makes a ton of difference. My car now runs around 82C while driving (thermostate fully open) casually. When stepping on it, it goes a bit up. At the end of the drive I let the car sit with the engine running without AC. The temperature then goes up to 104C when both fans come in at low speed cooling down to 100C when they switch off again. With AC on the fans will continuously at low speed so I guess then the car will hold the temperature down (unless outside temps are really high).

My solution: 1999 Porsche 3.4L I cleaned the radiators, replaced leaky hoses, flushed the system twice and installed a 160 thermostat. That was not giving me the results I wanted to see while driving around town or stuck in traffic. It has and will continue to be over 100 degrees in the Bay Area. What I did was: all of the above and the fan low/high jump. With the a/c off the car's temperature will not go higher than 104c. What I have been doing while around town is turning the a/c on low, with the low/high jump, the makes the fans blow at full speed. This was my last resort as it feels like ghetto rigging, however, it works. Note, if I know I will get stuck in traffic I keep the a/c on low. Conclusion: the car runs fresh at ~87c and most importantly the oil gauge reads at 1.5 bars.

...

Hi all I'm considering going down the electric water pump option designed by these guys: http://daviescraig.com.au/category/ewp-kits-combos The results are pretty convincing and they have some great ideas too, such as the water pump/fans keep going after the engine has been switched off if the temps are high, so no heat soak etc. Pretty much dial in the temp you want the car at and the system maintains it at that temp regardless of how you're driving... Costs are about the same for the parts, and fitting is probably 2-3 hours at least. And its all bolt-on/bolt-off, no modifications etc. I'd love to hear Jake Raby's thoughts on this idea! Rgd's Timlin

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Sounds like 21st century stuff! Question is what kind of volumes are required for the M96. I like the idea, keep us posted!

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Electric pumps were quite common on hotrod builds over 20 years ago. The problem with modification to any M96 engine is that the cooling issues are also a factor of how much heat can be removed by the front radiators. After you put in a low temperature thermostat, you still want the fans in the front to extract the heat. I don�t think the water pump on the M96 has much trouble circulating the fluids. That�s my opinion based on how the temps have risen and fallen on my car - almost all of it seems to be mostly a factor of how much air is past the front radiators.

The CEO of the company that owns Davies Craig is one of my customers. I have been using these since they came out, and was the first to test their newest systems, and the EWP150 as well. We've had one in use since 2008. Nothing new here....

Jake Are they good/bad/not worth the hassle? The heat soak removal sounds like a great idea as does the "dial-in temp" and for get. Can you tell me about the the installation? Where dis you mount the pump for instance? Were any mods required to get the fans talking to the controller etc? Any details you can provide will be greatly appreciated. I've spoken to DC and could only get as far as "they didn't know of a 996 EWP conversion in Australia yet...") The sales guy had a beautiful 550 Spyder kit car with a Subaru WRX engine in it though, and it was using a EWP - as you'd expect I guess! Anyway, any info would be great to know! Rgd's Timlin

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I use them as bypass recirculation, and for post cooling between track sessions. The 550 belongs to John Benson. He was going to buy an engine for that car from me, but he didn�t like it when he found himself at the end of the line that�s a year long...

Resurrecting this thread because how hot these cars run drives up my anxiety. How off is the Climate Control digital display? I have the following behavior on my car according to the climate control: Low speed fans kick on at 103c High speed fans kick on at 107c, car can reach as high as 110-111c before the high speed cools it down. Low speed fans disengage at 100c Car normally operates for me just a little past the 0. Is everyone here seriously driving around without the low speed fans ever engaging on their own?

If your airco is on, your low speed fans are on, always. I only switch my airco off (and thus the fans) when I enter my driveway, to prevent the car acting as a vacuum cleaner for leaves etc! Since you will have your airco on when it gets warmer anyway, it is a perfect match. Make sure both kick in, otherwise you have limited effect.

This is what I do also. Keeps my anxiety level at zero.