How hot is too hot?

I'm used to my cars temp gauges being pretty much static but the 996 moves around quite a bit. Freeway cruising it stays pretty constant around 180 but during "spirited" canyon runs or stop and go traffic it gets as high as the "0" in the 180, pretty close to the 3rd line on the gauge. Is that normal? My Aprilia bike temp gets the pretty hot when not moving (as high as 225, when normal temp at speed is around 175) with no detrimental effects but how much fluctuation do you guys see? Currently have Joe Gibbs 0W-40 in the motor. Thinking that's too thin for Socal and will switch to 5W-40 next change. Will that help at all?

JG offers 0w40? Or you meant DT40? What year is your 996?

If you read some other threads on this issue the first problem is that the coolant sensor is not at the hottest part of the coolant circulation system. Then there is the accuracy of the gauge. If you can resolve those 2 deficiencies we can discuss specific numbers with some confidence we are all talking about the same thing. Otherwise it becomes difficult to progress beyond anecdotes. The Track guys have this all resolved because a mistake could mean an engine rebuild. They may be a better source of accurate info because they may have calibrated the stock gauge against more accurate instruments with better sensor locations?

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Yep DT40. Car is a 99.

DT40 is already 5w 40. I don't think that will change your engine temp though. Have you checked if the radiator fans are working on both the low and high settings?

How do I check they are coming on in both high and low settings? Is getting up to the "0" on the gauge cause for concern, keeping in mind it's in stop and go traffic in 80 degree plus Socal temps. Once I get moving the temp drops back down to the 180 range.

That's exactly why I asked. The fans are supposed to turn on when you are in traffic and the engine temp is too high. I'm not saying your temp is too high though. If you have Durametric, you can activate the fans with low and high settings.

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No, getting up to the "0" is not cause for concern. If it goes beyond that, still not really a concern, but I'd start looking for why. Here's after an hour through the desert at 90 to 100 mph:

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Thanks Cuda. My gauge is right around where yours is when I'm moving at speed. Just gets up to the 0 when stuck in stop and go typical Socal traffic or getting on it going uphill in the canyons for a prolonged period of time.

The 0 on 180 is fine in summer stop and go traffic or hard driving. Mine goes to the far right side of the 0 when it is really hot and this is all fine and normal on my 2000 996. On my 2013 GTI the needle never moves, just sits at 180 or whatever it is and that is it.

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👍 Thanks. That puts my mind at ease.

Also check that your rads are clean and free of debris that gets picked up off the road.

Sounds fine but if youre interested, you can remove the position 19 and 21 relays and jumper them to see if you low speed fans come on. if not you may have a dead resistor. And definitely clean out your rads (bumper off)

When was your coolant changed last? Porsche says it's lifetime coolant but that's probably not a great idea.

How many miles does your car have? Have you changed the coolant? It's not lifetime. By lifetime porsche means until something else breaks that will force you to change the coolant anyway.

The 180+ on your temperature guage looks normal to me. It's common in the water cooled engines to go to 230 or even higher during hard track use and Porsche says the 0W-40 is fine. And no, the 0W and 5W are related to low temperature viscosity and won't help at high temps. Going from the 40 to the 50 might be appropriate for very high ambient temperatures, such as in exceptionally hot places like the desert or the Middle East countries. Some people do that viscosity increase for high mileage engines, and for those with higher oil consumption.

Car has 73k miles. Coolant was replaced in 2013 at 60k miles by previous owner when he did the waterpump, new tank and low temp thermostat. Rads are clean. I checked them when I removed the front bumper last month to have it resprayed.

On my 2000 C4, the gauge warms up to the left half of the zero in 180, and slowly moves to the right side of the zero when in stop-go traffic. On the move, it settles in on the middle to left half of the zero on 180. All fans seem to come on when they are supposed to and the heat never gets higher than the right side of the zero. The same was true for my 2000 black cabriolet prior to sale as well. Temp needle behaved pretty much the same before and after I put in a 160 degree t-stat. From the sounds of it, your car is behaving normally.

Porsche and a few other mfg put the temp sensor at the exit of the heat source(engine). Most other, and I think all Japanese cars put the temp sensor at the exit of the thermostat area. Since the exit of the thermostat regulates the temp, if you see any large changes at this point on the car, it's cause for concern. On a Porsche(at least all the water cooled ones I've had), you will see the unregulated temp of the engine, even though it is not the hottest point of the cooling jacket. Therefore, you will see more swings in the temp gauge as the engine(heat source) works harder. To validate this, in any other car when first starting out, note the temp gauge indication as the car is driven. As the engine warms, the temp gauge will go up to the setpoint, and maybe just slightly higher when the thermostat isn't open. Then, there will be a rapid but short decline as the thermostat opens and the cooler water flows in from the rad, followed by normal regulation. This doesn't happen in the Porsches I've owned.

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Interesting - I plugged in my VPAK reader on a drive yesterday and the coolant temp it showed was pretty dang close to what my gauge was showing. For what it's worth, mine runs about 188 degrees on freeway, then spiked as high as 210 when slowing in bad traffic.

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^Exactly the same on mine^... I even put a center radiator in over the winter. No difference in overall operating temp. I would imagine that if I'm pushing it particularly hard it should stay slightly cooler (than it would have without the center rad).