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  #16 (permalink)  
Old 07-09-2019, 11:34 AM
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obviously with the thermostat closed the coolant just circulates thru the motor
thermostats open as heat hits circulates around the bottom of the thermostat
it can open 0 to 100%, varies according to temps

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  #17 (permalink)  
Old 07-09-2019, 01:38 PM
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Some engines leave the bypass open all the time, like said above a small amount of coolant may flow but not enough to make any difference, since most will take the path of least resistance, the large radiator hose.

Some newer engines block off the bypass, that's what the extra spring loaded disc below the thermostat is for. If the thermostat is closed the disc allows coolant to flow through the bypass. As the stat opens the disc pushes against the bypass opening and seals it off.

One engine that will get a lot of folks in trouble is the old Ford 351c, 351m, or 400s. They will take what looks like the same stat as every other Ford engine or even the Chevy small blocks, but there is a bypass port just below it, and the correct stat has a small brass "top hat" on the part of the thermostat that contains the wax that moves it open and closed. If you use the regular stat it'll idle fine but run hot at speed because the open bypass only let's the coolant flow around the front two cylinders. The correct stat the top hat goes into the bypass port to close it and causes the coolant to circulate properly.
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Old 07-11-2019, 05:06 PM
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BBC Bypass Feature

Someone mentioned the bypass on a BBC earlier in this thread. Some folks plug the intake outlet and the water pump inlet in hopes of decreasing the likelihood of overheating in traffic on a hot summer day. All things being equal, plugging those holes does force most if not all the hot coolant into the radiator. You'd be amazed at how much water moves through that little BBC bypass hose, and none of it goes into the radiator to shed its heat. It goes right back into the engine just as hot as when it came out. What must be done when plugging that bypass is to replace the stock t-stat with one that has 3 3/16" holes in the top hat of the t-stat (or drill those holes yourself in a stock high flow t-stat). Stewart Components offers those drilled t-stats. Those will hold back enough coolant to bring the motor's operating temp up quicker. Of course the t-stat will fully open when the motor's temp causes it to do so, and ALL the water will enter the radiator. I run a 454 BBC in my '32 Ford roadster and a 502 BBC in my '41 Willys, both of which have those modifications. Never had an overheating problem in either, and I reside in a hellhole called Texas.
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Old 07-12-2019, 04:24 AM
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I shrunk my bypass fittings and hose down to about 3/8" for that reason. Didn't seem to make any difference in cooling, but I don't have a cooling problem either.
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