Re: 282 head unknown hole size

Posted by DavidPackard On 2021/1/31 17:56:43

Jerry;
I thought most temperature gauges before the war were mechanical, and inserted a bulb into the engine, in the case of Packard, in the aft portion of the cylinder head. The bulb would typically have a sealing ring or gasket to inhibit water leaks placed between the engine casting and the bulb flange. The threaded gland nut would ‘push’ onto the bulb’s flange and subsequently compress the sealing ring/gasket. Ok if that’s the design that Packard used before the advent of electric water temperature gauges, then the gland nut threads would not be tapered, because the intimate contact between the bulb and nut would not be guaranteed with tapered threads.

This business of using mechanical temperature gauges extended to at least the mid 50’s. As a young man I owned a ’55 Chevy, and that car surely had a mechanical gauge. The shop manual for that car talks about an ‘O’ ring . . . no mention of material . . . to seal the bulb . . . I just looked it up.

If the car is/was equipped with a mechanical temperature my vote would be the threads are not tapered, and therefore not NPT. 3/8 pipe would have 18 TPI with a diameter about 0.675 (remember it’s tapered), which would be something like 0.050 larger than Howard’s recommendation of 5/8 X 18 UNF.

dp