I've been following this discussion with interest. If I could find a bypass thermostat housing and a proper bypass thermostat, I'd install it. Apparently, the NAPA number doesn't actually bypass. Did I read this right?
I also have worked with heavy truck engines and realize the importance of the bypass system. It's common on many gas and diesel engines. BMW even used such a system on cars, as did Mercedes diesels.
Here's how it looks on the road. I have been running a 235 in a pickup that's worked really hard pulling a camper out West and I've been concerned about hot spots. I had the head off for no-lead seats a few years ago and noticed scuffing on #5 cylinder that indicates it's run hot. I believe that #5 is a hot spot and that's why they put the temp. sensor at #5 on the head. hot spotting is not a problem in winter, of course because the heater valve is open. But in summer it's closed. Running on a mountain highway in summer, when you come to the bottom of a long downhill the temp gauge will read south of 160, starting up the other side the engine is a full throttle with the therostat closed and the internal temperature comes up very quickly. Often, mine hits 230 by the top of the next hill. Then, going over the top the engine cools very quickly until the thermostat has a chance to close (2-ton radiator). So with a properly designed bypass system the temperature swings would be reduced. And bet of all the hot spotting would be much reduced.
