Coolant Temperature

Car is a '99 C2 6 spd Trying to get the car ready for track days and the coolant temperature is something that is still bothering me. I am usually in the low 90's for temp on the A/C hack when traveling on the highway, but when vehicle speed drops below 40 or so, the temp creeps up to 100-105C. All in mid 80's (F) ambient temperature. I have a new thermostat, waterpump, new fan relays, and have pulled the bumper and cleaned the radiators. Both fans are working and on both speeds. Low is on from the get go since the A/C is on. High is coming on at 103C, but doesn't appear to do much as far as cooling the car down any. I had originally seen temps up to 108C before doing this work, so there has been some progress in the right direction, but the last thing I want is to overheat the car doing a track day. Interesting to note is that 103C on the A/C hack is 210F on my OBD scan tool. Right now I am telling myself that I'd turn the car off if I got above 110C on the A/C hack or the needle crossed the mark between the 180F mark and the end of the gauge (looks to be 225F or so). Does anyone know what else I can be checking and what temperature does the car turn on the overheat light on the dash?

That's about what mine runs. Sounds pretty normal. Did you upgrade to a low temp thermostat when you replaced it? Those are highly recommended. Also, if the light starts blinking, it doesn't necessarily mean overheat. It can be coolant low or ambient engine temperature. Mine started blinking when I first got my car right as I was pulling into the driveway. I shut it off and towed it up to the garage. Only to be guided by forum mates to figure out my ambient engine temperature sensor had come loose and was sitting on the engine. PO had taken it to the dealership and they said the car was just cranky. Rennlist solved it in under an hour.

When warmed up, my car lives with the needle between the 8 and 0 of the 180 degree numbers, so I'm guessing I mine stays about 182� F under normal conditions. I live in Alabama where it is miserably hot.

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Same here in California with a 2000 MY cab.

Have you tested the temp sensor? When car is cool, check that the temp reading is close to ambient. Or remove sensor and heat it to 90c and measure the resistance. My car hardly never runs to 90c in traffic or track. Usually temp is 80c and stays there.

My '01 C2 normally runs the same as Nick's. Between 8 and 0. That's with a/c off. When I come to a light after getting on it, it will creep up to the center-right of the middle of the "0", but then the fans kick in and it comes back down.

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identical to mine. Good to know. I watch it constantly

Keep in mind that the water temp your'e seeing on the gauge are a "general" reading. It's not unusual for the temperature to fluctuate up and down somewhat but the needle won't budge.

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Check to make sure both of your radiator fans are operating at both the low- and high-speed settings. I'm surprised that your a/c unit hack is reading that far off the mark from the OBD scan tool reading. Other comparisons I have seen have been closer between the two. Maybe your sensor is shot? Overall, I think your temp reading are pretty normal. The 996 runs very warm... +1 The analog dash gauge is just a "dummy" gauge. It does not give you an exact reading by any means.

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Agreed. I used a Durametric to check the sensor temps and saw them vary +/- 5 deg C with fans kicking in and out. About the highest I've seen is 100 C (plus a low fraction) or 212 F. That's before fans kick in.

I'm going to replace the coolant temp sensor. This morning the AC hack was showing 27C(81F) when outside temp with my phone was 68F. This was right when I turned the car on. I appreciate all the feedback, hopefully this clears up the issue.

Update- Coolant temp sensor replaced, readings between the AC hack and scan tool are a bit closer, but the scan tool is still reading ~5F lower when I went for a drive today. I was still able to get the AC hack to read over 105C when I did the "air bleed procedure" after changing the sensor. The fans managed to get the temps back down below 100C with it just idling afterwards, but it was a pretty mild 75 degree day and have little faith that the system would keep the car cool if it was properly hot outside. I can't see a low temp stat fixing this issue. I could see how a third radiator might help a bit, but the car stays plenty cool when it's moving, just stop and go below 40 mph is a problem.

Low temp t-stat is recommended regardless.

this is what my temp gauge reads when hot, I had been driving for about 45 minutes at this point in 81 degree heat.

ejdoherty911, Are you running a low temp stat? Do most people here run 50/50 coolant/water? I suppose I could thin out the coolant a bit to improve the thermal conductivity, but I like knowing I'm well protected for the days its -15F in the winter. Slakker, Here's my issue with the low temp stat. If the cooling system was operating properly and had no issues keeping the car between the full closed/full open range of the low temp stat (say 160-180 degrees) there would be no issue for me. What I do not want to do is open the tolerance of the engine's operating temp. I do not want the engine to run between 160-220 degrees. I am guessing that the OEM stat is full open at 200-205 degrees since Pelican has it listed at 180 degrees opening. I could understand hitting 210 degrees or so a hot day (100F) in severe stop and go traffic. But hitting close to 220F on a mild mid 80's day either says the system is undersized or that it's not operating properly. I'm leaning towards the latter since the majority of the posts here are saying their cars never go above the 190-200F mark. The question is what is not functioning...I have eliminated the water pump, thermostat, dirty radiators, fan operation, and the coolant temp sensor. Seems to me that the only things left are clogged tubes that are lowering coolant flow through the radiators.

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Stock thermostat. I don't mess with the coolant, bad idea. I purchase OEM coolant, I wouldn't even consider anything else and follow the directions exactly as far as 50/50.

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ohlins, don't think about the coolant like it is antifreeze. Always run the recommended mix as it is actually like buying concentrated (enter your product here). The water is to turn the concentrate back into full strength coolant.

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Um - don't want to be a noodge, but 'coolant' is synonymous with antifreeze. The job of the coolant is to transfer engine heat to the radiator for dissipation. Since ethylene or polypropylene glycol is a lower thermal coef than water, using less in the mix will improve the cooling capacity of the 'coolant'. For the OP, I would suggest the low temp T-stat. I put one in a few weeks ago, and it's a great investment. I do not track, but I was sitting in city traffic today with the AC on full and the temp around 90F and the gauge never got over the tick at 180. It used to sit between 190 and 200 on the gauge.

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Anti-freeze is not synonymous with coolant. It is true that anti-freeze can be used as a coolant and it is true that anti-freeze is a component of most coolant mixes but not all coolants (e.g. water) contain anti-freeze therefore they are not synonymous. The point was that there is more to a coolant concentrate than just its anti-freezing properties and that each coolant concentrate is engineered to work best at specific concentrations. Yes, I'm well aware that water has better thermal conductivity than anti-freeze mixes. When I was growing up it was common to add anti-freeze in the winter then flush the system and replace with water in the spring. There is more to modern coolants than merely conducting heat away from the heat source, they also contain corrosion inhibitors, possibly a component to lower the point of solidification appropriately, possibly some lubricants even coloring agents. Thank you for your information to the OP about the low temperature thermostat. I have been looking for post that contain real-world results from their use. After a one or two hour ride at 75-80ish mph and then pulling into stop and go traffic when it is 110+ out frequently makes me a little nervous because, while the cooling system eventually catches up the system seems overwhelmed for the first few minutes after entering traffic.

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This or some electric problem that makes the ignition timing late. Doubt that it's the timing thou... Dirt inside the radiators will reduce heat dissipation, even if the flow is still close to normal. Mayby test with some coolant cleaner and a good flush first? If there is dirt/smudge in system, you should try to clean the whole system, not just the radiators.

Here I do experience exactly the same issue as ohlins8990 describes. I live in Southern Alberta, so heat would not be the biggest issue. Also changed water pump, thermostat to 71C, new expansion tank cap. still comes to a boil when idling too long. The last thing I can come up with is clogged radiator. Since its going from left to right(as I read somewhere), I'm about to change the left radiator(or both) as soon as I learned of more issues with the 996 radiators.

Stupid question, but can anyone provide some info about the "A/C hack" - I did google it Thanks

https://rennlist.com/forums/996-foru...agnostics.html

Thank you Jimmy

Just double checked. Needle in the middle of the 0 on 180 is 217degrees according to the AC.

From the link that Jimmy B posted: "Forget about the climate control "diagnostics" - they are pretty much worthless. I have both a PST2 and PIWIS tester and those climate control "diagnostics" never match up with the Porsche tool readings. Buy the Durametric software/cable and get the same information Porsche gets with their expensive diagnostic tools." -Loren I would do as Loren suggests

Except that the Durametric doesn't show engine temp for the '98/'99 model years.

So, why is it that the a/c panel shows one temp, and the tools show another? Different sensor locations? Just trying to learn....

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That's normal behavior. At highway speed air is being forced through the radiators and the coolant kept cool(er). If you slow from highway speed to surface street speed without the air flow through the radiators the coolant temperature will rise and can rise until the radiator fans are switched on to at least low speed (by my observation at 212F). High speed is switched on if the temperature climbs to 216F. It can take some time before the temperature comes down. There is a lot of hot coolant and it is hot because the engine is hot and there is over 400lbs of hot engine. Might add that every new MY one of the points Porsche makes is "better aerodynamics" and "better cooling". Unfortunately with a '99 MY you are starting with a car that has the original cooling system which mainly differs in how efficiently air is routed through the radiator ducts and this is somewhat determined/affected by the aerodynamics of the car. This aerodynamics is important. I can tell you my 2003 Turbo can cruise down the highway -- and has -- in 118F ambient temperature at highway speeds (75mph -- this in AZ) and the coolant temperature gage needle doesn't get above the "180" hash mark. The A/C was on so the fans were on but the cabin was at a cool/comfortable 72F and the cabin fan was not runing very fast at all. The temperature is of course hotter than that being around the 200F. (The temp gage is a very crude/imprecise "instrument" and is really only good for knowing the engine is cold, warm, hot (up to temperature hot), and too hot.) In even less heat -- 116F -- my 2002 Boxster's coolant temperature was "pegged" at 226F and both fans were running at high speed. I had to shut off the A/C because it was blowing hot air. Might note while the coolant temperature was at 226F it didn't get any higher. No warning lights came on and the engine was unaffected as that was years and hundreds of thousands of miles ago. The above highlights the difference in aerodynamics and of course cooling capacity. The Turbo has 3 radiators, the Boxster just 2. Be sure the radiator duct rubber sheeting is properly positioned. I've seen this sheeting move out of position but why I do not know. The passenger side of my Boxster has the sheeting hanging down into the opening in the bumper and I know this can and does affect the amount of air flow through that radiator duct. I have in the past managed to when the car is hot from being run and then sitting in the sun force the sheeting back into place without having to take off the bumper cover. It takes some effort as it is pretty heavy/thick rubber. With the fans running on low speed do you feel about the same amount of air being blown out from the fans' exhaust side? With the engine up to temperature is the air about the same temperature? You can get two relative inexpensive digital thermometers and tape them so each's temp probe is in the air flow and then check the temperature reading. Just because a fan is running doesn't necessarily mean it is spinning as fast as it should be. I had one Turbo fan that was running yet the air flow from behind the fan was pathetic. The tech checked and found no fan motor stage errors but did note the fan motor was drawing lots more current than the fan motor on the other side and I had him replace the fan motor. In another case -- earlier -- I found one fan not blowing any air at all. What had happened was the fan motor shaft had snapped. Tech said he had never seen a fan motor fail like this. For tracking often times the track prohibits the use of anti-freeze. So many use a water wetter. This will not protect the engine from freezing. Whether it contains any anti-corrosion additives or additives to help lube the water pump seals I don't know. I do not know if this water wetter is "better" at cooling then a proper blend of anti-freeze and water. My advice would be to install a 3rd radiator. I'm relucant to advise you to make aerodynamic changes but one change that has been proven to be helpful in the past with other cars is to install an air dam. This of course hangs down and forces air to flow around/over the car rather than under the car. This lowers the air pressure under the car and this lower pressure helps pull air through the radiator ducts. But you want to be careful the air dam doesn't deflect and create lift.

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TIL there's such a thing as "water wetter."

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Even crazier that it actually does what it claims in keeping things cooler. Water with water wetter added is a far superior cooling agent to pure water or water and anti-freeze. Or course it doesn't keep the liquid from freezing like anti-freeze does.

On the 99 model hot coolant is fed to the top of both rads simultaneously via a y pipe from the back of the car then cooler fluid goes back to the engine via another y pipe to the water pump there is no transfer from one side to the other it's sort of both together, I get this problem also looking at a third rad, kits can be expensive but you can pick one up from a breakers because tip cars are usually fitted with a third rad as standard so there's usually a good chance they will have one in stock! Don't forget the special pipes also there's two , one splits the hot feed to the left rad going into the third rad and the other splits into the cool side on the right , this just increases the radiator surface area, oh there's also a duct you will need to mod your bumper in the middle!

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Yup - it's great for some applications (like intercooling) when you want to transfer heat but don't need to worry about boiling or freezing...

A bit of info for the forum. I got a new obd bluetooth tool to datalog. Had a fairly warm day today so went for a drive around town. Avg. speed was 24mph. Most of the time the A/C display was reading 105-106C (~222F) QNi17c6.png KCwb7x9.jpg

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Finally had the time to check this, Durametric does show the ECTS value, on 98 at least. I have the 6 version, but I think that all versions will show this data.

Just to add another data point. I hooked my OBDLink MX up to the 996 yesterday and took it for a spin around the city. It was only 97 out and I didn't do any high speed runs so it never got above normal temps but I had my wife riding shotgun, She held the Android and checked the readout against my callouts. I would say that my dash gauge is pretty accurate. The first tick mark to the right of 100 was 120. When the gauge showed 180 the actual was 181 and then it went to steady state middle of the 8. That was 183 degrees. I do have a problem after prolonged high speed going into bumper to bumper in the summer. Here is my take on the "normal" solutions. Low Temperature Thermostat: I'm not qualified to remark on its long term merits to the reliability etc. of the engine but I am quite sure Jake and Charles are. Since it starts the circulation of coolant roughly 20 degrees cooler, it stands to reason that the engine will run cooler at light load. It also means that it should recover more quickly from increased load/decreased airflow because its steady state will presumably be lower. Probably useful. Center Radiator: First when Porsche put in the tip transmission they added a center radiator. That suggests to me that the dual radiators were very near their design limits. The addition of the automatic was enough to need more cooling capacity. The problem I experience is that the coolant gets uncomfortably warm after a long freeway run followed by stop and go in the middle of summer so ambients of 110-120 or so. How warm? Don't really know but it approaches the tick mark above 180 sometimes and I prefer seeing nice even, never changing engine temps, like most cars today. The two radiators are set fairly far back with essentially ram tubes to feed them through stylish but rather small (Mk1) bumper inlets. Further they sit behind the A/C condensers. I feel that at low speeds the ram effect is insufficient to keep up with demands (at least in AZ in the summer) when transitioning from rammed air to ambient plus fans air. The center radiator adds cooling capacity. It also is not hampered by A/C heat exchangers. Of course it also doesn't have a fan and on a Mk1 does not even have an exit duct but still... It is on my todo list. YMMV. Besides the rant I just wanted to point out that the gauge can be useful if you check it against another source. Mine is pretty much dead on.

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I double checked mine twice before posting. Thought it was weird that it didn't. I'll look again. On the LNE thermostat: "The factory thermostat starts to open at about 187 degrees F (86 degrees C) and only fully opens at almost 210 degrees F (99 degrees C). This means that the engine needs to get very hot before it starts sending its coolant to the front radiators. For this reason, I recommend installing a low-temperature thermostat in place of the factory one. LN Engineering has developed a thermostat that starts opening at 160 degrees F (71 degrees C) and is fully open at about 180 degrees F (82 degrees C).

I find this thread very reassuring - when I first got my car I thought it was running very hot but it appears it's behaving perfectly normally. Still going to do the low temp thermostat thing at some point though.

OK; for educational discussion I ask, is there any impact to the other sensors, etc. running at a cooler temperature. I offer the following discussion points. Caveat: I was a Chrysler tech in the 70's, and some of these points might be out of date. Which is why I'd like educational discussion. 1. Running a t-stat full open all the time can create some issues. As an example, with older cars, if you just removed the thermostat completely, the cars would overheat on the freeways. Odd, right? Well, the issue was that with no restriction, coolant would pass *too quickly* thru the radiators and never have a chance to cool. So, some restriction (i.e,. t-stat) is pretty much required. 2. On somewhat current-gen cars (personal experience on 2002 GM car), driving with a t-stat stuck in the full-open condition would often result in a code being thrown in that the operating temp would not be achieved soon enough, throwing off the emissions controls. The engine would "see" the cooler temp and provide an over-rich condition, over-riding the O2 sensors, and leading to overheated catalytic converters. So, if a low-temp t-stat were installed, how do our 996s compensate for condition #2 above? Personally, I'd love to install one of the LNE parts; am just a bit apprehensive based on professional and personal experience. Would love to hear your thoughts.

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Cool. The car I sold to buy my 996 was a '74 Charger, had it four years and brought it back from rusty wreck to (nearly) show car. Then I realised I hated driving it Apologies for going off-topic. Of relevance to this thread is that I ran the Charger without a thermostat for a while and had exactly the problem you describe.

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Carl, I was curious about this as well. It seems likely that emissions will be somewhat higher, that the car will reach its emissions ready state later and could even throw a CEL if it sees too long a not-ready state. If it wasn't from LNE I wouldn't even consider a LTT. I assume that Jake and Charles spent a lot of time getting to a setup that still was within parameters but lowers the thermostat opening threshold enough to make a difference. Still I won't use it unless the center radiator proves insufficient.

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Ohlins, is that really the normal state of your engine temp? I have only seen a temp like that once, after doing 80-85MPH for about 90 minutes in 118 or so temps and coming to a complete standstill in construction traffic. As it was it took several minutes to get that high and only stayed there for maybe 4 or 5 minutes. Since we're getting a bit theoretical: I have been giving this a lot of thought. I would guess that the A/C hack, the gauge and the OBD2 port are all using the same signal. It seems like your gauge and your OBD2 give similar readings so it seems the gauge is calibrated correctly. The question is, is that the same signal used by the ECU internally? I know that there is a higher resolution PID for engine temp but I also believe it is not supported at least on the 3.4 engines. I think that looking at an OBD2 reader, the gauge or the A/C hack should be essentially the same thing. The question is what does a PIWIS, PST2 or Durametric report? I would seek out someone that can run one of them on your engine. Maybe there is a problem on the ECU and you are not getting accurate readings. Just a thought.

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The picture is about where the temp peaked just above 220F. If the ambient is, say, 75F or lower, the gauge points to the left of the 0 in 180 which is about 190-195F on the OBD. On the highway, the temp stays over in that region as well. But once I hit any sort of stop lights in >75F, the gauge starts swinging over. The temps I'm showing in the chart are about I high as I've seen, but 210F in traffic is the norm with it being around 90F outside. It's also worth pointing out that it cools off rather quickly with the engine off. I've driven cast iron block cars that would still have heat in them after an 8hr shift. The 996 almost has the gauge pointing to the first mark in 30 min or so. Another completely unrelated data point: My other vehicle (at least with obd2), is an 06 Saab 9-7x. It normally has been hovering at 200 +/- 5F in the same ambient temps. For giggles I decided to try to overheat it. Revving it up to 3-4k in the driveway I was eventually able to get it up to 217F, but as soon as I drove off, even 10 mph, it cooled right back down to 205F.

Data points from my car as follows. In 90F weather, highway: - 75MPH cruise with no traffic, needle is between the 8 and the 0 in 180. - 25ish-MPH moving traffic, needle goes to the middle or 2/3rds way through the 0. In 70-75F weather, city driving: - if the engine is already warm and sitting around the left side of the 0, after about 20 minutes of stop and go (I hate SF streets), temp is at the far right edge of the 0.

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I would not consider that normal. Maybe I've just been lucky but I have had two 996s, in AZ--in the summer, and neither recorded temps like that. They both got close to there in the right conditions, as stated before, but neither stayed there more than a few minutes and normal driving was and is needle somewhere between mid 8 and mid 0 depending on ambient and fun factor. Have you pressure tested the system?

VivG, sounds very similar to what mine does. Tharbin, is yours 6spd or tiptronic? I have not pressure tested, no reason to suspect it has any leaks. Coolant level doesnt drop and the couple times I've pulled the cap with it warm, it was still under pressure.

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6-speed. Just looking for possibilities.