Resolved - Car running hotter in cold weather than during the summer

I have noticed during the last few trips around town (mix of highway and surface streets) that my car seems to be running 3C or 4C hotter (93 or 94C vs 90C at highway speeds) than it was during the summer (based on the climate control hack). Yet the ambient temperature is 20F to 30F cooler. Key facts Car is a 1999 C4 I think I get a whiff of coolant smell when the car starts or I shut off the automatic climate control systems. It is really faint disappears quickly and could just be paranoia. There is no evidence of a leak anywhere and the coolant level is normal. High speed fans seem unable to pull the temperature down below 94C when in traffic (I need to test this more at highway speeds though) Replaced the expansion tank cap in August Cleaned the radiators in May and visual inspection shows no major obstructions Oil weight is 5W50 and pressure is good Am I just being paranoid?

Not sure of the year, etc. but if you are not running the AC due to the current weather, then your front cooling fans might not be running and causing your temp reading to be higher than in the summer, just a thought...

Thanks added detail. It's a 1999. Good point. The HVAC is in auto mode, but you are right the fans may not be engaged due to the ambient air temp...

I have a 99 also and it took me a while to become "ok" with my temp flux, Somethings I notice about my car On hot days, it runs hotter. No matter what speed On the HW it does run cooler. But on hot days. hotter than normal In traffic it runs the hottest, But it doesnt get out of hand. no matter how hot or cold out, it never overheats. When it heats up. It takes a long time for it to come back down.. even if ti go from traffic to hw driving. I used to get a wif of coolant too.. But it was a leaking water pump. I could smell it before I could see the leak.

Relax and enjoy your Porsche. I'd say the internet is partly responsible to our Porsche fears whatever they may be.

My temp needle always sits right in the middle of the zero in 180, or slightly to the right of the zero when in traffic. Not sure what that translates to in numbers though.

I wouldn't worry about it. If you're at 94C around town, you're doing fine... at least if my car is any indication. And I have never not once seen the high speed fans lower the temperature that far sitting in traffic once the engine's got itself all sweaty. The thing to bear in mind, especially with the Mk1 cars, is that airflow has a far bigger impact on operating temperatures than ambient temps do.

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with this logic, the fan should (and will) help in traffic.... I did the fan mod, (manual on/off) and within a few minutes , when I manually turn on the fan...it brings my temp down noticeably.

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The fan mod essentially lets you turn the high speed fans on sooner than the car would do automatically. Those who've done it say that intervening with the high speed fans sooner prevents the engine from getting heat soaked. Those who don't say that the fans will come on at 102C anyway, and the result will be the same. I don't know what the truth is, but I haven't been persuaded enough to do the mod myself. What I will tell you is this: Toronto has the worst commutes in North America, worse even than LA. I find that in traffic like that, the engine eventually reaches a point where nothing is going to get temps below 100C again except movement, no matter when your high speed fans activate. An asterisk to all this: My understanding is that the Mk1 cars seem to run hotter because the only sensor for reading operating temps is on the engine itself, whereas the Mk2 cars average their temperature readings from two sensors, one there and one elsewhere... maybe at the rads. Assuming this is true, it would explain why people often report such radically different experiences with operating temps.

I hear you on heat soaked cars.... those take time to cool off. my mechanic also told me that modern cars (996 included) are designed to run hot for better emissions.... so I believe under normal conditions (excluding track) these temps are normal on the 996..... We rarely see an overheated 996 thread here, just hot temp threads are common.

I had one fan not work on low speed. Replaced the resistor thing (a little bit of a pain to take it out) and it solved a slight running-hot problem on my car.

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Any change in coolant temperature is cause for concern. Haven't the time to read all the posts so forgive me if I repeat something but be sure with the A/C off the radiator fans come on of their own accord. My info is the fans should come at 212F and shut off at 205F. If the coolant temp continues to climb the fans will switch to high speed mode at 216F. High speed shut off temp is 205F. A bit of anti-freeze smell could be an early warning sign of a coolant leak. If cap not a new one (part number ends in something less than '03' or '04') you might consider as a preventative measure just replacing the cap with a new one. I have no experience with a 996 but my 986 on mild days can get rather warm if the A/C is off. With the AC off the coolant temp will climb -- in traffic, slow going, waiting in long slow line at drive through food window, etc -- until I hear the radiator fans come on. Then the coolant temp will drop (I've observed this using the in-dash temp gage needle (crude) and by monitoring coolant temp in real time using an OBD2 code reader/data viewer/logger) to 205F at which point the fans will shut off. If I continue this type of driving for long, the fans will cycle on and off over a span of several times. In some case I hear the engine compartment fan kick on. It turns on at 135F (IIRC) and I do not recall at what temperature it turns off. The in-dash temp gage needle can move a bit close to the high temp side of dial, sometimes 3 or more needle widths past the 180F mark. But as long as the coolant level is good, there is no pressure leak, and the fans are working ok I've never seen any overheating problems. And I've driven in some pretty hot temps (116F). 'course in this heat I had the A/C on. I wonder about the fan mod? I have never had any desire to have a manual control of the fan speed. I wonder if the mod is interfering with the normal automatic triggering of the fans into low or even high speed? Sincerely, Macster.

Additional info. Both fans are working properly (just checked) Have done the fan mod (it works properly) Reservoir cap is new. Coming home tonight, the car warmed up to normal operating temperature and seemed good for while. When I finally got out of traffic and into clean air and accelerated up to 110 kph, the temperature actually rose until it steadied at 95C. It then actually cooled slightly to 92C (with the high speed fans engaged and full heat on) when I exited the highway. As such, I am going to 1. Pressure test the system (maybe there is a leak somewhere that I cannot see) 2. Clean the rads again. Hope it is not the WP.

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If it is the WP..... then thats good news.

Well, it's not a obstructed radiator as I cleaned them last night. Also did an inspection of the WP area and visible hoses and could not find anything that indicated leakage or seepage.... Other than a failing expansion tank, what might it be...

Fergus, does your engine compartment fan come on?

No, the car never gets hotter than 95C at speed, and even idling it takes a while to get to 100C. What I have noticed is that if I accelerate hard I can bring the temperature down from 95C to 92C within a few seconds.... I am starting to think that it may well be the water pump or the tension on the belt.

My 996 acted exactly as you describe in the summer months but never actually got hot. It bothered me as well watching the needle inch up in traffic on hot days. I went to the cooler thermostat from L&N when upgrading my Boxster engine to a 3.6 and it runs below the 180 mark and thus far has not moved once up to running temps.

I'm curious about the LN thermostat, but skeptical for the same reason: I see how it can delay the engine getting hot, but I don't see how it can ultimately prevent it. Like the fan mod, it brings intervention to the table sooner, but it doesn't change the cooling capacity or the cooling process at all. Especially with the new rads I put in last year, I find my car's cooling system works a treat... unless it's sitting still on a hot day for a long time. Then, even with all the fans whirring away, it gets hot and stays that way until the car is moving again. To me, a helpful mod would be an aftermarket fan blade that moved more air. That would actually make a difference.

Have continued to monitor this issue. My indie mechanic has looked at it and cannot find a pressure leak and on the scan tool shows it operating 3C lower than the climate control display and generally within spec. This said, since my original posting I have observed the following 230 km trip to Montreal - temperature consistent at 90C or 91C ; return trip from Montreal - temperature consistent at 94C or 95C - External temperatures within 2C or 3C and dry Trip to Montreal in pouring rain and some snow - temperature consistent at 84C to 86C Trip to work - temperature climbs to 90C on highway and immediately drops to 84C upon exiting highway. This behaviour is quite common. It will drop 2C or 3C at least upon slowing from 110 kph to 70 kph or less. I also find that driving in clean air (i.e. no traffic) results in the car taking much longer to get from cold to 90C+, when compared to driving in traffic where the air flows are presumably more turbulent. My only thought is that perhaps I have a wonky thermostat, but until the temperatures go well beyond the normal operating range, I am not going to worry about it any more (but will monitor, given my paranoid tendencies )

Finally found a small leak in the expansion tank and replaced it. Replaced the expansion tank cap with a an OEM one and installed the LN Engineering 160F thermostat. Can runs measurably cooler.

Fergus - good result...pleased to hear you've won after such a long time I've followed your cooling issues and believe that your original thermostat may not have been opening to its full open position. The only other suspect would have been the water pump not operating 100% efficiently. I had quite a similar problems as you had and elected to replace the T'stat (160 deg), water pump and coolant together. Temp gauge now sits @ 80 deg unless in heavy traffic.