foxj0001

Here in Northern CA as in many other locales in the US we are dealing with very high temps - currently over 100°F on many days.
I had my 2018 991.2 GTS Cab out on an errand yesterday afternoon and parked in the sun for maybe 20-30min after a short (30min) drive at speeds between 25 and 75 mph, averaging around 55-60. Oil temp steady @225F, coolant steady @180F or so.
Upon driving off the overheat alarm went off, with the coolant sensor in the red zone (>250F) with an alarm message to park the car immediately to let it cool down.
I did exactly that, and over the next 5-10min watched the coolant temp gauge drop in steps (rather than smoothly) back to the usual operating temp of ca. 180F.
I started her back up, drove off, and all seemed well until about 5min and <1/2 mi later the same situation occurred - coolant apparently >250F, alarm, park the car, etc.
I let that all happen again and upon restarting I turned around to head back to my mechanic (whose place I had just left, for an unrelated issue - slow leaking tire).
However, the alert did not recur a third time, and after driving along for another 1/2 mi or so I decided to turn around again and head home (the same 30min drive away at mostly highway speeds).
Did not get another alert, even when passing slower traffic at increased speed.
Q: Was this an environmentally triggered (high ambient temp, direct brutal sunshine) on the coolant sensor? If not, other thoughts? First time in 5yr and 20K miles I have ever seen this on this car. NB oil temp never wavered from 225F the entire time, and no excess activity of cooling fans seemed apparent.

arter

Feels like the coolant system was not circulating ( water pump?). Oil temp hadn't jumped up yet, but the water jumped quickly.
Could also be sensor,but not likely because of the sunlight.... Check fluid level once cooled off.

shammerman

Not the weather.

2013gr911

I had this issue on my 991.1, was a failing change over valve

Iamlost

Had this issue too, exactly as you describe.

I had to have the valve replaced as discussed above.

—-

991.2 & Texas heat

foxj0001

Many thanks to the respondents, especially arter - you were spot on.
Had the car to the mechanic today to mount and balance 4 new shoes (they were original factory mounted PZeros, with almost 20K miles, owed me nothing, but an embedded Phillips Head screw at the inner sidewall forced my hand).
My guy is an Indy shop and a real pro. If you are in or around Sonoma County CA and need your baby properly cared for tire-wise, go see Bill Pagnano. He is fastidious and looks to have your shoes properly mounted with below-spec limit run-out and so well mounted that he applies a minimum of wheel weights to perfectly balance). I’ve no commercial interest in Pagnano Automotive, just a shout-out from a happy client for a true artist. But I digress.
Up on the lift I ask him about my recent coolant temp adventure. He says Oh, I was going to show you this when we got done with the tires, come on over here - shows me the crusty dried coolant on a pipe under the water pump (see picture). Your water pump is leaking he says, better get it fixed, shame on Porsche this is practically a brand new car, etc etc. Dealer Service Mgr replies to email with parallel assessment, don’t drive it, have it towed in, covered by warranty, etc. Whew!
Bill topped off the coolant and I took her the 20mi home to await Porsche Roadside Assistance to tow her tomorrow.
So again, thanks to my PCar brethren fanatics for the quick assessments and advice. Could have been a lot more (negatively) dramatic had I chosen to run her for any serious mileage in a “spirited” manner!

Josh(PA)

Do a search for coolant pump failures here. When the pump goes bad, you will often get coolant in the vacuum lines. Porsche has a procedure to replace the lines with the pump. I had a 2nd overheat issue a few months after my pump leaked and it was due to coolant blocking some valves.

foxj0001

Hi again
Car was flatbedded to the dealer this morning. Just learned that they need to replace not only the pump but the valve block as well. I took Josh's advice above and flagged vacuum lines to them.
"Parts on order". Guess I will have to live without her for a bit...