Do thermostats get 'lazy' over time?

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I recently replaced the original thermostat in the Fusion. Using my Torque app, I noticed that the coolant temp would never get above the high 170s. As time passed, it almost never got over 170. OE thermostat temp is 190, and after thermostat replacement, coolant now sits between 190 and 210, depending on driving conditions.

My Sedona has the original thermostat also, which is rated to start opening at 180. Using the same app, I've noticed since I got the van that the coolant rarely budges above 177. It loves to sit there. Occasionally it'll bounce above 180, but then drops right back down. I ordered an OE/Aisin replacement and will report on the results. For the Fusion, restoring the higher (normal) coolant temps has resulted in better gas mileage; back to where it used to be.
 
Calibration deteriorates over time, they stick open,closed or anywhere in between.
 
Supposedly according to what I heard on here, good quality thermostats fail in the open position, cheap ones fail in the closed position allowing overheating.
 
Don't the Japanese/German OEM ones tend to last longer(10 years) than American ones? I'm still running the originals on the family fleet - all OEM Toyota/Kuzeh. I've heard unless an code involving ECT is triggered, it shouldn't be touched.
 
I have installed 3 thermostats in two of my Buicks over the years. They all gradually failed by opening too soon, causing the engine to run too cool. All my replacements have been o.e.m. Tried an aftermarket and it looked poorly made, and performed poorly too - replaced with an o.e.m. within a week. They are inexpensive and easy to change, so not a big issue.
 
Originally Posted By: carviewsonic
I have installed 3 thermostats in two of my Buicks over the years. They all gradually failed by opening too soon, causing the engine to run too cool. All my replacements have been o.e.m. Tried an aftermarket and it looked poorly made, and performed poorly too - replaced with an o.e.m. within a week. They are inexpensive and easy to change, so not a big issue.
Had the same thing happen on my 05 LaSabre, changed the stat again and all is well.....can't remember changing stats ever in the 60s and 70s this much....
 
I had the same symptoms as the OP in my old Cobalt after about 10 years. Eventually it threw a code. That was when I replaced the thermostat.
 
Yes.

My wife's HHR always ran rated temp of 185 per the DIC. The fan failed bringing the system up to 240. Ouch! Something happened to the t-stat and now it always runs 180.
 
Originally Posted By: CourierDriver
Originally Posted By: carviewsonic
I have installed 3 thermostats in two of my Buicks over the years. They all gradually failed by opening too soon, causing the engine to run too cool. All my replacements have been o.e.m. Tried an aftermarket and it looked poorly made, and performed poorly too - replaced with an o.e.m. within a week. They are inexpensive and easy to change, so not a big issue.
Had the same thing happen on my 05 LaSabre, changed the stat again and all is well.....can't remember changing stats ever in the 60s and 70s this much....
My dad had a Volvo back in the '60s which had summer and winter thermostats, changed out in fall and spring.
 
Originally Posted By: Chris142
Originally Posted By: NormanBuntz
Supposedly radiator caps do.
i test every radiator cap I touch. About 75% fail.


How do you test them?

Do the OEM and Slant ones fail?
 
I can't recall one failing since approx 1974. And that was on my mom's car where it failed closed. I've never had one failed on one of my cars...and don't recalling changing any out over the years. Though, the auto shops could have done them with upper radiator hose/water pump jobs. Weren't too many of those either.
 
To me "lazy" means that the thermostat starts to bind at the shaft so that it cannot fully open or close. But in most cases a thermostat that starts to bind will get fully stuck rather quickly. So I don't believe that a thermostat could be in the lazy condition for long periods of time.
 
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Mine is a 6 year old 2 1/16" MotoRad 195. It has always seemed a bit slow to open on the first warmup of the day. This has gotten worse in the last few months with the coolant temp going higher before the gauge settles back to normal, and it is not just on the first warm up of the day, but nearly every time.



A have a made in the USA Stant superstat 195 ready to go.
 
Originally Posted By: Donald
Originally Posted By: Chris142
Originally Posted By: NormanBuntz
Supposedly radiator caps do.
i test every radiator cap I touch. About 75% fail.


How do you test them?

Do the OEM and Slant ones fail?
pressure tester and look at the rubber seals. They all wear out
 
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