I have a 1991 4X4 that I bought new. It has 215,000 miles on it and is going strong. I am having a problem, though. I'm in Phoenix, and during the summer, the engine runs significantly hotter than the rest of the year. When this occurs, I lose my oil pressure when the engine idles. I have to step on the gas a little to keep the pressure high enough to keep the gauge up and the low pressure idiot light off. Any ideas?