Morning sir! I noticed you pulled your shutter stat in your last picture. I've been trying to remember if my fan has ever kicked on and i don't think it has. Could you point me in the right direction of the location of the shutter stat? Did you end up cleaning/rebuilding yours by chance? I can't find rebuilding in the TM anywhere. Everything i have found on them is for a NHC250. Thanks again for all your help!
Good Day Sir,
The S-Stat kicks on as the last-attempt to cool the engine down, T-stat opens around 180' (allowing additional cooling via the radiator) and S-stat opens around 195' (provides additional cooling by means of forced-airflow across the radiator and block). Also to note, the removable fender-wells direct the airflow across the block when the fan is on, having them removed will actually stop the engine from cooling down, so if you ever go into an overheat condition, don't open the hood and remove the fenders to allow for more air lol. Somewhere in the TM I remember reading that warning.
On the S-Stat, the position of the plunger inside is normally closed, receives pressure from air system to open when it reaches a certain temp, provides air to fan clutch, fan-clutch spins fan, more cooling air is provided, etc. It's possible that you haven't had it come on because you never reached the higher temp ranges? Or, it could be stuck in the closed position. When I mentioned the fan coming on in the previous reply, that was because I didn't have enough coolant in the system and it started to overheat. This was the only time my fan came on owning the truck, it never got to those higher-range temps needing for additional cooling since then. Eventually, my S-stat started leaking air from the weep-hole on the back of the unit, so I bought an o-ring rebuild-kit from
Big Mikes Motor Pool and he has a step-by-step breakdown on how to rebuild it on YouTube. It wound up being a $25 fix instead of a $300+ part replacement.
I'm not sure how you could test the S-Stat function without intentionally going into an overheat, since the thermo-coupler inside detects that condition and activates the plunger to allow air through to the fan-clutch. Providing air to just the out-let side would engage the fan-clutch, bypassing the detection-function of the S-Stat, but that would only check to see if your fan-clutch is operating. Have you gone into an overheat condition and confirmed your fan wasn't spinning?