How does this help?
Ive seen this before but, I'm unsure as to how this really works. Could you elaborate?
how does it help? well, the simple answer is it doesn't really. the point of a coolant bypass is to relieve pressure building up in the coolant passages in the back of the head to avoid blowing out the gigantic freeze plug back there, thus barfing coolant all over your transmission where it definitely doesn't help at all. it also allows hotter coolant to circulate out of the back of the head more easily rather than having to fight with other coolant paths to get back into the main stream of flow. it's very useful for high-horsepower builds where the engine is going to be turning high rpm (above stock redline) frequently, or where the driver puts the truck under extremely high load (heavy towing under hard boost) for long periods of time (EG towing in the mountains at or near max GCWR). the vast majority of us, this is just an extra insurance thing and not really needed.
how does it work? there's a housing which bolts to the superfluous transmission support holes (replaces them) on the back of the block around the aforementioned huge-by-large freeze plug. in this housing resides a 180* thermostat (in the fleece kit) which works exactly like you'd expect a thermostat to work: it starts opening at 180 and is fully open by about 190-195 to allow full time flow out the back of the block and along the passenger side of the head. this dumps into the thermostat housing and reenters the coolant circulation path. the fleece kit comes with the housing, the built-in t-stat, the hose, the t-stat housing spacer, all fittings, and some clamps to hold the line in place. it's a really nice kit. the other option is the motorsports kit, which is basically exactly the same except in place of the thermostat there's a Watts-type pressure valve in the back which opens and allows flow at a given pressure - 35 or 50 psi, depending on what source your're looking at.
how do i know that? because i'm one of those people who recognizes i'll likely never have a need for this thing, but after losing my water pump in spectacularly catastrophic fashion, i bought everything i could think of to mitigate it happening again. so i'm now running the fleece coolant bypass, a sinister coolant filter, a 180* main t-stat, and while i was in there i replaced my upper and lower radiator hoses, the belt, the pump, and the tensioner. because anything worth doing is worth grossly overdoing. i came up having the mantra hammered into my head that if you show up to a gunfight and find yourself in a fair fight, your tactics suck. therefore, if i expect the truck built (eventually) to ~700 horse (i'm shooting for 670), i want everything capable of handling significantly more than that. i went with the fleece kit because the price is virtually identical and while the motorsports kit provides theoretically better warm-up (or rather less of an obstacle to warming up), i've only once in my life experienced a thermostat failure where one stuck closed. i can't attest to the reliability of the Watts-type pressure valve as i have zero experience with them, so i stuck with what i personally have confidence will work. not saying the motorsports kit is worse or the fleece kit is better, just saying i don't have any leg to stand on from experience with a pressure relief valve like that.
but that's just my two cents. hope it helps.