Engine thermostat technical design question.

[Outdoors_Guy_88]

I finally had to replace my stock 2015 thermostat due to thermocycling occurring since around November (between about 190-210 F) with changes in throttle load.  After the swap it ran rock stable again at 210 F.

 

I have changed many thermostats over the years (usually failed open or failed closed), this is the first that thermocycled noticeably with out sticking in one position.

 

My question:

I noticed there is an extra coil spring and little plunger off the bottom of the "bracket" that supports the main spring and traditional thermostat.

 

Anybody know the purpose of that extra spring and plunger?

 

BTW, I tried heating the defective thermostat in boiling water and the main thermostat opened as it should, but that spring/plunger device on the bottom didn't appear to do anything  (maybe the cause of the failure).

 

Ideas?