12v owners. I installed a Stant 13479 thermostat over the weekend. NO more wild 50* temp. swings from the old thermostat. Just nice mild 5-10* swing on open and closed. Got the idea from ghostman over on the other forum. Very very happy with the results. Truck actually made temp. on my way to work this morning in the 37* cold. It would have been barely off the 140* mark with the old tstat.

I believe we are saying the same thing in a slightly different way.

 

It's import to bypass during warmup - the NAPA/Mopar/Stant stat's lack of a bypass disc doesn't prevent the bypass flow - when the stat is closed, the bypass is open, and fulfills it's primary function of circulating a trickle coolant through the head. The engineers should have made the rear freeze plug divert as well, but that's easily fixed. On my setup, I divert the stagnant #5 & #6 coolant to my heater core inlet via a Keating Machine tapped freeze plug insert.

 

When towing, and the stat opens to regulate temperature, the bypass closes - this doesn't really cut down flow through the upper rad hose; I've heat gunned the difference back to back on the same day before & after the stats opened. The tiny bypass doesn't really have a chance at affecting a fully open stat's monster flow that these very stout water pumps facilitate.

 

I'm not concerned about the bypass function, as its only there to

close & prevent flow through the bypass passage when the thermostat is open & provide 100% flow through the rad hoses.

 

The bypass hole is too small to make a difference to cooling flow whether closed or open; its primary function is to ensure a bit of coolant circulation when the thermostat is closed, to help avoid hot spots while warming up.