The gauge in your truck was intended for a 216 engine, which struggled to make 15 pounds of hot oil pressure. The 235 runs anywhere from 25 to 50 PSI depending on engine temperature. The "reconditioned" oil pump we put in John's 261 engine when we built it would put out 70 PSI on a cold start, and drop to 30 or so at a hot idle. Somebody had probably tinkered with the relief valve on that one! It sounds like your engine is doing what it's supposed to do. Any oil pressure at all indicates the pump is producing more oil volume than the engine needs for lubrication, but most people like to see that gauge at midrange or above all the time. It's theoretically possible to lubricate an engine properly at zero oil pressure, but all of us like to have a little buffer zone where oil pressure is concerned.
If you can find a dash gauge for a GMC stovebolt, it's got a 60 pound full scale. Original gauges are a little scarce and pricey, but I think some of the resto-ripoff guys have newly manufactured clones for sale.
Jerry
