RagTop
Old Grumpy
Since I moved to the Sierra foothills almost five years ago, my Mustang has been struggling with the summer 100*+ temperatures. I have 50K miles on the rebuild and have been using Castrol 10W-30. It's beginning to show the effects of a three speed automatic and lower rear end gears (lots more rpms per mile). I am considering going to a heavier weight oil but am torn between the Castrol 10W-40 semi-synthetic or the Castrol 20W-50. I used the 20W-50 for years in a first generation Mazda RX7 I owned, and managed to avoid the dreaded apex seal failures so common in rotary engines. I doubt that the car would be seeing extremely low temps around here, so the 20W wouldn't be a problem. My rebuild included a high volume oil pump and, when the temperatures are around 70* with the 10W-30 it runs with the oil pressure gauge at about 7/8 gauge. When the weather heats up, the car runs with the oil pressure gauge registering between half and 1/3 depending on rpm, showing the effects of the heat on viscosity. I don't want to cause problems for the engine with excessive oil pressure either. Any advice would be gratefully accepted.
TIA
TIA