Car overheating.....

I guess I bragged too soon. Using the DIY for removing/replacing the coolant expansion tank in the 996 after my original tank was leaking, I got thru the project and everything seemed great. I took it for a hard drive last nite and it seemed to be ok. Today, it's starting to over heat a bit when at a stoplight, and the idle seemed a bit rough, but is running around 650 at idle. It stalled one time at a light, and it's never done that before. It hasn't happened again. I didn't get any CEL's...so I don't have any clue as to where to look or what to do. When I'm driving at freeway speeds, the gauge remains between the 0 and the 8 like it's supposed to....but if I sit at a stoplight for any length of time, the needle starts creeping into the 0 and just slightly to the very outside right edge of the the 0. Before now, it always ran right between the 8 and the 0 like most other 996's do. When I pulled into the garage, it was running a bit into the 0 and the front fans were running. I've looked at the oil dip stick and there's no foreign residue in there...there's no foreign (oil) residue in the coolant tank, so I can rule out a head gasket or crossover problem. Can anyone tell me what I've done...not done....done wrong...need to do? Chuck

No 996 expert but Porsches are hard to get full of coolant. When I had to have a radiator replaced in my Boxster dealer service tech used a tank that pulled a vacuum in the cooling system -- enough the rubber coolant lines collapsed -- and then turned a valve that closed off the vacuum port and opened a valve into the coolant reservior and the coolant was drawn into the system by the vacuum in the system. No air pockets. I had my doubts but took car for a shake down drive of several hours in hot July (is there any other kind?) heat of Wichita KS until I was satisfied there were no leaks and no overheating issues. Be sure cooling system completely free of any air pockets. Any air pockets present can result in very localized hot spots developing that can flash even coolant to steam and in doing so the steam works to prevent liguid coolant from getting to the hot spots. Left alone, this can result in head gasket failure due to uneven heating/cooling of head. Sincerely, Macster.

Make sure you have a pressurized system. After driving the car to fully warm, let it sit for 4 hours or so. Slowly remove the fill cap and you should here vacuum being release. If you do, the system has no leaks and is fine. It is also helpful after adding coolant to the tank to idle the car for 15 minutes with the coolant cap off and then shut it down and elet sit for a few hours or more. This encourages any air in the system to escape. BTW: Temperature guage in the middle or high side of the "0" is normal for the 996 in warm temperatures and around town drving. Fans will run.

I've seen dealerships run the engine for extended periods at high revs to 'burp' the coolant system. Seemed to do the trick - but it seemed a little harsh as a spectator.

Hi Chuck, we're almost neighbors. I had a similar problem that I found impossible to cure. Niello Porsche in Rocklin has been great about helping me. My problem was a line that was crimped by the front passenger side radiator (I think it was some kind of vent). I never would have found it. My car was a burn victim that I rebuilt....so I was pretty familiar with the cooling system. Good luck with yours. If you get too frustrated give them a call. David Welling is the Service Advisor and he has always been great about letting me talk to the mechanics (ask for David again). They're open Saturday and he might be able to talk you through it. Hopefully I'll meet you in person one of these days at a local Porsche event.

Chuck, I almost forgot...if your temp. seems high with this weather, You'll definately have a problem come summer. Mine did the same exact thing. I replaced the cap, tried "burping" the air out, etc. Niello saved me a lot of frustration. It's no fun driving and having to constantly worry about watching the temp. guage. Again, Good luck.

Mark: Hello neighbor....thanx to you and the other helpful Rennlisters. I've heard about this burping process. I know that I followed the DIY instructions to the letter...even used the foil turkey roasting pans to catch all the coolant that I had to drain from the bottom drain.... I know that earlier in the day when I first saw the coolant drippng from the tank...I have no idea how much I lost...so I just replaced whatever I lost with distilled water. From what I've read, water has a better cooling factor that the coolant itself....so the addition of what I imagine is about a quart of water shouldn't dilute the coolant to the point it would be the cause of heating. The ambient temps this time of year are only in the high 40's thru the low 60's....so any heating irregularities now will definitely only get worse as the temps warm up. What get me is that I had no problems before this other than the leaking coolant tank...and everything went back just fine...I didn't even break the coolant level sensor (had a new one on hand in case). It was a bit of a chore getting back in...but as I said earlier...the DIY that I got from a link here to the instructions in Renntech was dead on. I will try the burping procedures described in some of the responses tomorrow. I did notice a bit of a coolant smell again today at one point....but I couldn't see anything dripping...I'd hate to think after all this hassle that it turns out to be a hose or some other innocuous thing. You can't really get under it and look up and see much of anything....the muffler and shielding cuts off the view. What about a thermostat? Again logic tells me everything was A-OK with the exception of the leak....so just putting in a new coolant expansion tank shouldn't have precipitated another problem. Tomorrow is Saturday and I'll try giving Niello Porsce a call as you suggested Mark...thanx for the tip. Can anyone advise if adding just water and no additional coolant would contribute to the heat rise in any way? Logic suggests not because as I said ealier, research tells me that water is a better at soaking up and countering heat than coolant. I have enough in there to take care of our "low temps"...which seldom go below 25 degrees. Only once this year did it get close. Not like you folks up north.

I just did a FAN mod on my 996. I read about it here...I think. All I did was add a switch to the factory fans that by passes the thermostat and can be turned on anytime I want. I am prepping for the summer and sitting in LOS ANGELES TRAFFIC. As it is now...it creeps to the 0 but never gets farther... Anyway..the mod basically places a switch between the fuses so when the KEY is on...you can flip the switch and turn your fans on. If you leave the switch off..your normal thermostat turns the fans on. You also cannot forget to turn off the fans because as soon as you remove the key the fans turn off after a minute or so because there is no more power to the relays. Pretty easy mod that is useful living in a HOT city with TONS of traffic like I do.... I hope someone on here can find it for you...I will look around and see if I can find the thread.

Radiator Fan and Engine Compartment Fan Switch Mod The 3.4 996 runs extremely hot when driving around town in temperatures higher than 75 degrees. This mod is a way to reduce coolant temps back to a safer level, helping to reduce oil temps and improving performance. The mod consists of installing a switch that will allow you to turn on the high speed radiator fans at any time, while maintaining the automatic operation of the fans. We do the same for the engine compartment fan. Radiator Fans Connect a wire to the ground of the 2 high speed fan relays located on the relay carrier located in the driver�s side foot well. The relays are #20 and #22. Feed this wire to where your switch will be located. Connect the wire to one side of the switch. Connect another wire from the other contact on the switch and then connect the other end of this wire to a chassis ground point. With key on, this switch will now immediately turn on both radiator fans providing maximum cooling. When you turn the key off, the fans will continue to run for about 5 seconds until the relay shuts down. Your fan operation remains normal when the switch is off. 1999Porsche911 You can get more fancy if you want by installing a pickup wire off the speedo wire to the DME to have the fans shut off above a certain speed using a relay that will open at a specific current level.

may have air in the system, may just be normal and your being a little parnoid after doing the repairs youself...........I still do that on my own cars.......never figured that one out. The coolant should self burp. make sure the coolant level is ove rthe minum mark, and keep driving it, as long as it doesnt tsrat flashing the lil red warning light your not actually over heating.

Note: flashing red warning light can also indicate low coolant level 996 Burping technique here: http://www.renntech.org/forums/index...ic=775&hl=burp

as far as i can tell by reading other archived posts here and neurotically bugging the techs at my local dealer, that engine temp is supposedly normal. in stop-and-go traffic, my 2000 C2 engine temp invariably goes into the 0 of the 180 and then to the right of the 0. when you do that trick with the hvac unit to get all the readings, my temp sensor has read 104 degrees celsius, which is damn hot. when back to hwy speed, it will go back and disect the 8 and 0. what confuses me though about yours is the fact that it never went that hot before your DIY expansion tank replacement. leads me to think that my issue is not normal, after all. hmmm....

You ever had your radiators cleaned? They collect tons of crap - leaves, paper, dead birds! It's amazing what can get stuck in there. https://rennlist.com/forums/showthre...ning+radiators

yea, forgot to mention that. the porsche tech used a vacuum and got out plenty of leaves, cigarette butts, etc., but no change in engine temp. i even did a preventative coolant cap upgrade just in case. i'm a bit more confused now since Chuck had more normal temps before. i'm very curious to see if burping works for him. the tech checked out my whole system but didn't suggest burping.

Cant you just "burp" it with the bleed balve on the cap looking thingy forward of the fill cap?

yup you got it!! That is the mod... I also "cleaned" my radiators when I had my bumper removed for the airhorn install. They are right...all sorts of crap gets in there.!

Just to review, as I have posted these facts many times before: The 996 engines are designed to run at approximately 194F (coolant temp) and have little problem doing so as long as there is adequate air movement across the radiators. However, due to the design of the front bumpers as well as the smalls surface area of the radiators (including running with a 3rd radiator), speeds below about 60 mph do not provide the amount of moving air that is required. In moderate to warmer temperatures, your 996 will run hotter temperature when driving around town or at slow speeds and the coolant can reach 220F+ and the oil temp will rise accordingly. Temperatures this high greatly reduce the power to the car. One way to dependably maintain coolant temperature of around 195F in all ambient temperatures is to do the fan mod I wrote above. In designing this mod, I took into consideration that the fans would run as designed when they are not manually turned on. There are other ways to automatically run the fans such as thermo coupler change and speed sensor control, etc, that will keep the engine operating at 195F, but they are more involved and need a higher level of skill. One of the biggest negatives of hotter engine temperatures is loss of power since intake tempertures are hotter, fuel and timing is controlled partially by engine temperature, etc. For those who insist on using the Mobil 0W40, you will also find a better throttle reponse resulting from cooler oil tempertures allowing faster, more positive valve opening and closing. Operating your car as it comes from the factory with higher coolant and oil temperature higher than specified will not harm your car and most drivers will not even know the temps are higher than normal. However, if you are looking to recover some big power, this mod is one way to do so easily. You will be amazed how much more power a computer controlled engine running at 195F has compared to one running at 220F. Once your car gets moving above 60 mph or so (bumper design dependent), your coolant temps will begin to fall below 200F regardless of whether the fans are running or not. Doing the same mod for the engine compartment fan will also yield additional power by reducing engine temperatures. Bigger gains are found by those who run a modified intake where the air comes from inside the engine compartment.

I would try putting coolant not just water back in. It's worth a try and you can go to an VW dealer and get the coolant there. Do you have a coolant line running next to the tank that has a see through section (Clear hard plastic) that allows you to see if the lines have air in them? If you have air in the lines the coolant temps will rise when just sitting and just reving the engine will lower the temps. That least that what happened when I did a flush

Evansero wrote: Do you have a coolant line running next to the tank that has a see through section (Clear hard plastic) that allows you to see if the lines have air in them? No...I don't have any clear lines to see if air is in the lines....but air that close to the tank should purge naturally. 1999 Porsche wrote: Once your car gets moving above 60 mph or so (bumper design dependent), your coolant temps will begin to fall below 200F regardless of whether the fans are running or not....Yes, I find that to be exactly true. The minute I get up to 60 or more, the temp begins dropping almost immediately back to the mid-position between the 8 and the 0. I guess if I can't get to the bottom of this, I will have to do the fan switch mod as 99 Porsche suggests....but it's damn disconcerting to do my very first DIY and have it end up causing something that wasn't there before. I do know that I had to take out the sensor probe several times when I was installing the tank because it kept getting hung up on the other hoses and wire looms as I tried to insert the tank....so I took the sensor in and out several times and finally figured out that.....NOTE** THIS SUGGESTION IS NOT IN THE DIY*** I figured out that if I put the sensor back in as the DIY shows, but I took the wire clip off the sensor BEFORE I tried to put the tank back in...it was much easier and the wire didn't get hung up. Once the tank was wiggled into place, I could tip the bottom up a bit and with a pair of long nosed pliers, insert the plastic wire clip back into the sensor. The sensor sits in its own little recess in the bottom of the tank sealed off from the coolant, so even if you break the sensor, coolant can't leak out of the sensor recess....therefore the sensor can't contribute to any leaking problem you might have. cdodkin wrote: You ever had your radiators cleaned?...No, I haven't done that, but I will try that today just in case a plastic bag or something was sucked into the air scoop on one side or the other. I guess my last resort is to clean out the air scoops, and try running it hard again and seeing if perhaps it will "burp" (low confidence level on that one)....and finally...do the fan switch install. Many sincere thanks to all of you who have tried to help me work thru this dilemna. I'm sure that somewhere in all the suggestions the answer lies waiting for me to find it. Chuck

Thanks 1999 Porsche 911 for that. as long as i don't think i'm hurting the car, i'm ok. robbed power i can live with-- as long as i'm not on the track. however, what i find most odd is that there appears to be considerable variability in people's engine temps in similar situations. in Chuck's case, in the same car. in stop and go traffic, some people say it goes into the 0, same say to the right of it, some say no real change at all. is this possible or just a matter of people not accurately noticing their temps? the ideal temp for my car-- when cruising above 60mph-- is around 87 degrees celsius (188F). if i hit traffic on the hwy, it can go to 104 degrees (219F). after opening up getting back up to speed, literally in a matter of minutes, my temp will drop back to 87 degrees celsius. Although that's a significant change in temp, this appears to be normal. i guess my question is, as illustrated in Chuck's case, if his post-DIY temp is in fact normal, but it is a change from before, is variability in engine temp a function of slight differences in how the coolant system is set up or maintained? sorry for being neurotic, but this is pretty intriguing to me.

OK....I've gotta' jump back in....This morning I went out to the car and before I even started it up, I took a look at the coolant tank after it sat all night....It was dogone near empty! I put about 16 oz of distilled water in it and filled up the coolant tank to the max mark...but it was all water. There was no coolant in there at all. Previously I wrote that I had no confidence in the burp suggestions....but damn if that doesn't appear to be an issue. I drove it in traffic, but not for more than 15 minutes, and it never went into the right side of the 0. One thing that was apparent was that upon starting, the engine did surge a bit and idled rough until it warmed up. It never did this before...so the only thing I can think of is MAF...because I didn't do anything except disconnect the EVOM intake from the rubber hose and connect it back again when done. Doesn't sound logical that anything should have been altered, changed, or in any way different does it? I'm going to give it time to settle in....they say that the computer needs time to "learn".....but for just changing a coolant tank? I dunno... I haven't had the opportunity to really get it out and drive it for an extended period of time...but the initial manifestations seem to indicate the "burp" occurred when it cooled down, the coolant level dropped, I added distilled water....and it's possibly back to normal except for the hunting in the rpm level when starting cold. I'll give it a chance to settle down. This sounds an awful like much ado about nothing....hope it isn't a bore....but it's curious to say the least. Bottom line........all you folks have been great.

My guess is your engine will and always has reached temperature of 215F+ regularly when its 75F+ outside. You can't go by the temperature gauge a it does not indicate the correct coolant temperature. Use the climate control screen to look at the actual coolant temperature. To see it, do the following: Press and hold in the recirculate and the top (arrow up) buttons on the right side of the panel for a few seconds. The left screen will change. Using the + key below that screen, adance so the display reads 6c. Then press the center vent button once. The display will show you your coolant temp. To go back to normal, simply press AUTO.

Are there any other "tricks" that the climate control panel can do?

Move the setting to 20c and you will display your speed.

Do an archive search...there's a whole lot the climate control panel can do...it's been posted before and I was amazed at all the different engine measurements that you can access thru the control panel. I think if you go to the UrL of: http://www.cb-racing.com/boxster_AC.html you can get the instructions for all the "stuff" you can bring up....pretty amazing really. Chuck

Chuck, I am glad to see that I am not crazy! Last spring I purchased my 2000 996 c4 cab from my friend/business partner. I noticed that around town and definitely in hot weather it was running hot and smelling of anti-freeze. I asked my friend about it and he said "yeah, when they (dealer) replaced the expansion tank I started to get that smell and hot running." He took it to the dealer and they said that the smell could just be some overflow from when they filled it. I knew this wasn't right and brought it to them at least twice. They pressure tested it, ran it for hours at idle and confirmed the fans were on and told me twice that "this is normal" including the high temps. This makes me very nervous as Hot engines=dead engines=$$$$ in repairs. It is odd that these problems are after the tank replacement. I might try a fan mod but I am nervous as this is my first Porsche. Can anyone else weigh in?

2000996 where are you located ? how high of temps are we talking?

If you want to test it out, simply jumper the high speed relays as I discribed and run them full time to see what a difference it makes. No switch install, just ground the relays and you're good to go.

I would agree with you 99Porsche911 that the mod on the switch relay would make you "good to go"...but it doesn't address the dogone nagging problem of why in the hell does the car run hotter after putting in a new coolant tank? When I think back over what was done...I took off two fuel lines (17 and 19mm), two hold down bolts for the air pump, disconnected and removed the CAI, and disconnected three hoses that connect to the coolant tank...and lastly, disconnected the sensor at the bottom of the tank. Then I simply reversed that process and it was done....so it's really perplexing as to why something so overtly simple would produce a condition that didn't exist before. At the risk of sounding like a whiner perpetuating the issue, I think I'll put in the switch and hopefully be done with it....but it still nags at me. Especially because like 2000996 says....periodically I get another whiff of coolant....

I live in Upstate NY but it easily gets in the 90's here. It's been a few months since I drove it (now it's 7f!) but the temp gauge easily got to the "1 o'clock" position if not more. Well past 180

Thanks for sharing the tricks on the climate control guys, very cool...