Cooling question (please don't yell at me!)

I know this has been discussed to death, and I have done a search. But all the info is in little scraps, and my question is fairly simple. This is just one of those "is this normal for a 3.4l 996?" questions: in 85 degree F/30+ degree C humid temps, sitting in traffic (I mean, sitting, creeping along in first), temp can climb to just under the 100 degree C mark on the gage. The manual is frustratingly vague about this. No cooling fan is audible, but the temperature seems to stay controlled and the AC keeps merrily running. No rad obstruction. Also, very slight coolant loss. Let's say enough coolant is lost over 3 or 4 weeks to drop the level in the expansion tank from max to min. This is in the aforementioned hot weather. No smell. I have the updated expansion tank cap. Thanks in advance, and apologies again for the old topic, but I'm still learning this car.

Mine does the same...last summer I watched my coolant level seemingly drop (from max to min) on several occasions, then hold steady for months. On a few occasions, I thought I was loosing my mind, the level seemed to be higher one morning than the previous morning. I always checked first thing in the morning on a cold engine, so no chance of false positive. I had the updated cap, but not the updated tank. To this day I have not figured out the coolant situation on this car...other than resolving to accept regular fluctuations. As long as your overheat light doesn't start to flash (mine never did)...you might just relax for now. Others will tell you to replace the tank...which seems to go on these cars inevitably. Not a bad idea...but for now you're probably ok.

The temperatures you mention sound normal. I punch up the temperature on the HVAC and see temps in the range of 98-103 C in ambient conditions identical to yours. However, any coolant loss at those temperatures means you have a leak in the system. You need to find the leak, and fix it before it gets worse. This could be an indication of a cracked expansion tank and you certainly don't want to see that fail in a big way.

Your high coolant temperature is caused by various design flaws with the 996. The 2 biggest flaws include the restriction in the amount of air that can pass over the radiators at slow speeds and the fact that the radiator fan sensors turn on the fans too late and at too high of a temperature. Another contributing factor is the poor quaity of the water pump which causes it to wear quite quickly, thereby reducing the volume of coolant flow at low engine rpms. You'll identify this problem by increasing engine rpms to 1500 and watchiing the coolant temperature drop. The engine was designed to run between 190F - 200F in all conditions. These temperatures can easily be maintained by doing my radiator fan mod which allows you to run the fans at high speed when needed. At speeds below 60 mph, there is not enough air flow to keep the coolant at the targeted temperature unless the fans are engaged.

Bruce, I have noticed the EXACT behavior that you described, just yesterday. Fluids were topped off a month and a half ago. I check the fluids yesterday and my coolant has gone from max to min line. Like you, I have the new cap. I'm thinking of the doing the expansion tank upgrade, but man, I'm really not in the mood for that just yet. I mean, what's the worst that can happen (coolant leak, coolant all over the garage, stranded in the middle of nowhere), right? Anyway, and seriously, my mechanic said that the behavior is normal. If the temp gets too far to the right of the zero, or worse the overheat gauge lights up, then it's time to reasses the likely required tank replacement.

Its an expansion tank, it is going to vary, it acts as a buffer for the cooling system. When it is hot, the tank will have more fluid in it and vise versa.

+1, agreed %100 its a buffer and will vary betwee min and max, below min add coolant, over max, it will overflow out through the cap when pressure allows!

It IS NOT the coolant tank causing the temperature to rise if your have ANY coolant in the tank. It is caused for the reasons I described above. NO stock 3.4 996 engine will EVER, EVER, EVER (did I say EVER?), run at the factory designed temperature while driving in stop and go traffic in a sunny 75F+ ambient temperatures, period. The is no way to reduce the temperature without increasing airflow.

For those of you that have small coolant losses with no visible leaks, I'd be willing to wager that you have recently had to drain coolant (either to replace the expansion tank, replace a coolant hose, etc... Am I right? If so, here is my theory regarding the small coolant loses that so many of us seem to experience. In my case, the drops in level were very slow, but nonetheless a cuase for concern given that I have a 99 and losing coolant with no visible leaks is often a very bad sign. I first noticed my problem after I changed my expansion tank. I have since learned that it is extremely difficult to fully and completley purge the coolant system of all air bubbles that are inevitable following a complete or partial coolant change or flush, unless you take it to a dealer or indy mechanic with some magic equipment. So, when it gets hot, these bubbles, over time, come out on their own, causing what appears to be a drop in coolant. My level finally stopped dropping, and I was constant for months, and then I blew a coolant line, fixed it myself, and had to add a bunch of coolant. Guess what. I saw slowly dropping levels for a long time afterward. Driving around for about a week doesn't seem to be sufficient to burp the system of all the trapped air. That is my theory as to where my coolant is going, as it is clearly not intermixing, I get no smoke at all out the tailpipes, and my expansion tank and cap are new. Anyone else have the same experience?

After running your car, park it with the nose down and open the bleeder valve for the day/night. This will allow the air in the system to rise to the expansion tank and eliminate all air in the system. Then level the car and fill the tank up to the correct level. Or you can simply drive around for a few days with the bleeder valve opened. Problem solved.

1999Porsche911 Can you give me a thread or just tell me where the bleeder valve is located? I just replaced one of those great water pumps you just mentioned

ScottArizona, that's interesting. I did have the coolant flushed and replaced a few months back. There was a significant "loss" after that, which I put down to burping and which has not repeated itself. But I didn't know that there could still be air in there.

another coolain question: 1. what is the correct way to check coolain level? engine hot? engine cold? with it running/stop? 2. what is the correct coolain to use? can i mix them? in the stop&go traffic, my temp is in the middle of "0" of the the 180 mark. and my coolain level is right on the MIN mark when the car is hot. guess i need to add some coolain thanks

On the top of the expansion tank you will see the black valve. It has a metal ring on it. Move this ring to the vertical position and it opens the valve.

I actually drove my car with the bleeder valve open for 4-5 days. I did not try the inverted parking thing though. Maybe I'll sit it on jack stands for the night with the cap off to see how that helps. I've also heard one theory about the early car cylinder wall failrues being attributable to people not adequately "bupring" their systems after replacing coolant. the theory is that the areas where there are air pockets create "hot spots" that can harm the enginge, even though the overall engine temps are reading o.k.. Anyone else heard that?

Thanks, guys. Seems like maybe I should leave it alone and monitor it before I do anything expensive. Appreciate the help!