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rennbob

Are 996 / Boxster Thermostats Prone to Sticking?

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Now that my AOS / IMS / clutch replacement is done, my 99 996 with 103k miles seems to run a little warmer than I remember.

 

So I used to the purge valve to to bleed any air introduced by opening the AOS coolant lines.    I cleaned the rads and AC condensers, yes there was a lot of gunk after 15 years!   :D  

 

Neither helped much.  From cold start, 65-70F ambient,  it takes 9 miles to get to ~85C.  (4 miles of 40MPH non-stop, then 5 mi of 70MPH)  By comparison my Lotus Elise will be at 85C within the first 4 miles.  

 

The car will stay at 86-88C if 60+MPH is maintained, but monotonically increases into the 90s then 100+C if there is any stop and go.   It never easily seems to cool back down, even in long bursts of 40MPH.   Once on a clear highway at 70MPH it takes  ~8(!) miles to get back down to 87C.   Again for comparison, the Lotus will drop from ~97C to 85C in just a few minutes once it has clean airflow.  When idling, the 996 fans come on at 100C and takes 4-5 minutes to fan shutoff at 97C.

 

The slow warmup and cool down--"high thermal mass"--seem longish to me.   The water pump was replaced at 87k miles, but the t-stat is original.  Perhaps the thermostat is stuck partially open?   I haven't really pushed the high-temp stop-and-go testing yet.      

 

BTW, all temps are measured at OBDII, and I'm not interested in the 160F aftermarket t-stat.   Thanks.

 

 

 

 

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Now that my AOS / IMS / clutch replacement is done, my 99 996 with 103k miles seems to run a little warmer than I remember.

 

So I used to the purge valve to to bleed any air introduced by opening the AOS coolant lines.    I cleaned the rads and AC condensers, yes there was a lot of gunk after 15 years!   :D  

 

Neither helped much.  From cold start, 65-70F ambient,  it takes 9 miles to get to ~85C.  (4 miles of 40MPH non-stop, then 5 mi of 70MPH)  By comparison my Lotus Elise will be at 85C within the first 4 miles.  

 

The car will stay at 86-88C if 60+MPH is maintained, but monotonically increases into the 90s then 100+C if there is any stop and go.   It never easily seems to cool back down, even in long bursts of 40MPH.   Once on a clear highway at 70MPH it takes  ~8(!) miles to get back down to 87C.   Again for comparison, the Lotus will drop from ~97C to 85C in just a few minutes once it has clean airflow.  When idling, the 996 fans come on at 100C and takes 4-5 minutes to fan shutoff at 97C.

 

The slow warmup and cool down--"high thermal mass"--seem longish to me.   The water pump was replaced at 87k miles, but the t-stat is original.  Perhaps the thermostat is stuck partially open?   I haven't really pushed the high-temp stop-and-go testing yet.      

 

BTW, all temps are measured at OBDII, and I'm not interested in the 160F aftermarket t-stat.   Thanks.

 

Yes, they do sometimes stick open or closed, but I wouldn't describe them as "prone to sticking" any more than any other thermostat I have seen.   If you think it is bad, pull it an look at it; if it is stuck partially open, it will be obvious.  If it isn't, you could suspend it with a wire in a pot of water on the stove and monitor the stat position in relation to the water temp in order to determine if it is doing something stupid.  Or you could just pull it an replace it, they are not that expensive.

 

And regardless of how you feel about them, the 160F stat is a good idea in these cars.............

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Hey rennbob, what you describe is exactly like my 01 C4 Cab with 64k miles. Just did new water pump and 160 LN Tstat. Even with all that and a massive spa treatment for ac condensers and radiators I am surprised at how quickly the temp jumps up in any traffic. much like the stas you quote. Definately runs cooler overall withnew tstat but as might be expected not much relief in extremes

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heat exchanger. For emission purposes the exchanger heats the oil during warm up and helps cool the oil after warm up, therefore, this one of key reasons in slow driving conditions you will see your coolant temps raise. The advice above to test your thermostat to ensure it is working properly is right on, replacing with LN 160 is even better. Continuous Oil temps at 200+ F i

is pretty tough on your oil in these engines.

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