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I recently replaced the thermostat on my '09 Cayenne 3.6L V6 with a genuine Porsche thermostat along with water pump, belt, etc. Ever since I replaced it I've noticed that on the first start of the day, when the engine is bone cold, the water temp creeps past 1/2 mark and to the 3/4 mark sometimes before it settles back to 1/2 mark. Once it settles at the 1/2 mark it stays rock solid, no issues whatsoever in 100F ambient days in stop and go traffic.


Did I get a bad thermostat? It feels like a slow opening thermostat to me. Sometimes I think its in my head and maybe it behaved this way before I replaced the thermostat but to be honest I never paid attention to it until I overhauled the cooling system. Has anyone else noticed this behavior or can confirm it is a lazy thermostat?



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  • 4 weeks later...
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Follow up post for anyone who has this problem in the future. I replaced the thermostat with a new one and fixed the issue. I confirmed it was a slow opening thermostat when I removed the old one and put it in a pot of boiling water with the new thermostat. The new thermostat opened as expected while the faulty one did not open until later. Both thermostats were bought from the Porsche dealership.


Side note, the replacing of the thermostat on the 3.6L V6 is a PITA. It is in a hard to reach area with hoses and wire harnesses running in front of it guaranteeing that you will walk away with bloody knuckles.

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