| Crusing in the Passing Lane Joined: Jun 2011 Posts: 5,096 | The 503 in my GMC had a bypass housing also, however there was a piece of fence wire stuck in the original thermostat, so I used a cardboard thermostat on the way home from Jerry’s part of the country. Since those thermostats are no longer made, I put a small block GMC(Chevy ones are smaller, won’t fit) one in line of the upper radiator hose, works fine.
Ed
'37 GMC T-18 w/ DD 4-53T, RTO-610, 6231 aux., '95 GMC running gear, full disc brakes, power steering, 22.5 wheels and tires.
'47 GMC 1 ton w/ 302, NP-540, 4wd, full width Blazer front axle.
'54 GMC 630 w/ 503 gasser, 5 speed, ex fire truck, shortened WB 4', install 8' bed.
'55 GMC 370 w/270, 420 4 speed, grain, dump bed truck from ND. Works OK.
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