Driving w/ AC

How many of you guys drive with the AC on at all times? If I turn mine off, the temp will fluctuate more than usual. With the AC on, the temp will hardly ever move. It feels wrong to keep the AC on at all times though, so I'm wondering what everyone else thinks. All other cars I've owned in my life have had their temp gauge rise to the mid-level mark once warmed up, and would not move AT ALL, no matter if it was 120 degrees out in traffic, or a cold day in the mountains. I wonder why ours is so sensitive and susceptible to change so easily.

I run my ac when it�s hot outside and heater when it�s cold. It sounds like your plate (the one that spews black foam) is in the post spew phase and therefore is unable to adequately hold in the air. Several threads on DIY for correcting, but it�s a pain.

You are talking about your coolant temp gauge, not the air temp in your cabin, correct? On many other vehicles, the temp gauge is not truly a representation of actual temperature, but that the car is running in the normal range. You have "low" and "high", it shows low when you start up and then moves to the middle as it warms up....sits in the middle no matter what the actual temp is (as long as it is within the normal range), and only moves to "high" when you overheat. Dunno why you see more fluctuation without the A/C on other than the fans are probably running more often to improve condenser efficiency, maybe?.

I don't know about the 996 specifically, but in most cars, the radiator fans are primarily controlled by a thermostat switch that turns them on and off based upon coolant temp. However, when the A/C is on, it overrides the thermostat switch and runs the radiator fans all the time regardless of coolant temp so that air is constantly pulled through the condenser so that the A/C actually cools. If the coolant/engine temp is only steady with the A/C on, it seems like the thermostat switch might be broken, so the fans don't turn on and off properly based upon coolant temperature (but it works with A/C because turning that on forces the radiator fans to be on all the time). Again, the above is generic advice -- I don't know the specifics of the 996 A/C system.

I assume you are talking about the engine coolant temp. German cars have almost always given us gauges that reflect actual values and not "exceptions". On a Porsche (and Ferrari, Lambo, etc.) the oil pressure drops low at idle once warm and is high when the rpm is up. On a US or Asian car the oil pressure gauge stays centered. On a water cooled Porsche the engine coolant temperature gauge fluctuates with engine load, fans on/off, etc. On US or Asian car the gauge stays steady In the US the gas tanks stays on "full" for 100 miles or so. On a Porsche it starts dropping immediately. Why? I read an article in Road & Track (I believe) 30 years ago explaining that. In the US most drivers manage by exceptions. They seldom look at the gauge and if they do, they expect things to stay constant ("Normal"). There was some indication that this was possibly a carry over from pilots and others coming back from WWII who were so overloaded with multiple gauges even back then that they managed "exceptions. The fuel gauges in the US are calibrated to read the way they do because if the gas gauge moved off full too quickly people brought their car in complaining about poor fuel economy. So, US manufacturers calibrated the gauges so they don't move until the tank is 3/4 empty. Ever wonder why it moves so quickly once it moves off full? In summary...it's natural for oil pressure, coolant temperatures, oil temps, etc. to move.

AC on...fans come on and stay on...more consistent cooling...more consistent gauge reading. Sounds normal to me. Just drive it.

Consistent temp gauge when A/C is on is normal. Inconsistent engine/coolant temp when A/C is off is not normal in my opinion -- the radiator fans should come on when needed so that the temperature is as rock steady as it is with the A/C on. I'm pretty sure my 996 is always in the middle whether A/C is on or off, but I'll pay closer attention next time I drive it to confirm that.

As others have said, the water temp gauge is an accurate reflection of what's going on. Many of us have been lulled to sleep by other cars that just hold the water temp needle dead-center on the gauge unless it's wildly hot or cold. Those gauges could really just be replaced with an idiot light, since they're only showing 3 values: "cold start", "normal", "overheating", and nothing in between. So if you're used to that, seeing the needle on the 996 wander around a little can be unnerving, but it's nothing to worry about, and you can be sure it's happening in any other car you drive, even if the manufacturer is hiding that info from you! On a cool day cruising on the highway at high speed and low load, mine will run just to the left of the 180F hash mark. When running hard, it might move up to the middle of the "0" in "180". I wouldn't really worry unless the needle was moving significantly toward either end of the gauge. I drive with the A/C off on all but the hottest days because I just don't find the inside of the car gets very hot.

On my RX350, it stays dead center no matter what, even in the hottest of August while sitting in gridlock traffic driving around Houston, with the A/C on max and the seat coolers on full. I'm sure it's warmer than that, but that's where it stays, no matter what after barely a minute or two of warming up after driving. However, I had an F10 BMW 550i before this, and yes, it was a little unnerving at first to see the water temp gauge fluctuate so much depending on external heat, if the A/C was blasting, if the seat ventilation system was on, etc. So, getting into my 911 was pretty normal and I never even look at it. Granted, I bought this car in late November so it's never really been subject to true Texas heat yet, but the prior owner just lived over in Austin and said he ran around with the A/C in "Auto" mode all year and never had any issues. So until it starts creeping up near the right-side of the temp gauge I'm not too worried. However when I do sit at idle for more than say 5 minutes, I will turn the compressor off/on a little just to give it a break. I'm pretty positive it doesn't 'need' it, but like the OP said, down in my region that A/C unit takes a pounding. But in reality, if it breaks, I'll just get a new one that will work even better than it currently does so I shouldn't really be too concerned! I keep it garaged and under cover when I drive my 911 to work so it's pretty cool in the cabin anytime I get in, unless I'm running around town and can't find covered parking.