I live in the Sierra foothills, east of Sacramento, and the triple digit temps up here in the summer time were causing real problems for my mildly built 302. When the temperature got really high it would begin to lose oil pressure (I'm assuming the viscosity of the oil was being compromised). So I did my annual oil change last week and, on the advice of a friend, switched from Castrol 10W-30 to Kendall 20W-50. I hoped that would stop the oil from getting so thin in the hot weather. I took the car to a show this weekend and then out to burgers with my Mustang club. On the cruise the burger joint I wasn't looking at my gauges closely, but on my way home I looked down at my oil pressure and it was real high (I had the rebuilder replace the oil pump with a high volume model) so that was normal and positive. But then I looked over at the temp gauge and was shocked. In cool weather, like we had on Saturday, the car usually runs at about 1/3 the stock temp gauge scale. It was ticking along at about 2/3 of the scale and maybe 3/4 while I was on the highway. I actually started using my heater to dissipate some of the heat. When I got off the freeway the temp started to reduce to a range of 1/2 to 1/3 gauge. The last time I had a car that did this it was because the PO had overbored the engine excessively and it developed a pin hole in a cylinder wall. I checked my new oil to see if I had a chocolate milk shake in the crankcase and it was all clean and normal. It's got me worried that it might be a blown head gasket or a damaged block. My rebuild was 50K miles ago and it was overbored .040. Anyone have any suggestions as to what my trouble might be? It could be something as simple as a temp sender, but I doubt it since this coincided with the oil change. I guess I might have a stuck thermostat that is only partially open, but I doubt that too since the engine began cooling down after I got off the highway. Those puny Ford 20" radiators usually get overwhelmed after running at highway speed and not during. I am not going to replace my stock temp or oil pressure gauges with real devices, so my descriptions of "1/3 gauge" will have to suffice. Help!