i drive a bone stock all original 86 3.8/C5 3 spd with 2.73 gears and 124k miles.... the car has the most up and down oil pressure i have ever seen, even with all my finicky 5 liter cars...it doesnt matter what the temperature is outside, if i have the air on or off or if its city stop and go or not. sometimes the gauge is on the O O/R part of NORMAL, and other times its on the L, doesnt matter if car is warmed up or not, it just seems to fluctuate a lot... the second part of this problem is when i have the air on it gets really hot... normal is 180-190F, but with the air on it is 210 on the highway and as much as 250 plus stop and go...new radiator, thermostat, and antifreeze.... i just dont get it. the car has been converted to 134a (before i got it) being that it has aluminum heads and crap i dont like the idea of this old puppy getting to 210, 230, even 250?! she really runs like a top but i dunno.... and maybe there should be a non - 94-04 V6 forum?
Maybe you need a new oil pump? Or you could have a blocked coolant passage. Only way to know is to have a mech look at it.
I wouldn't sweat it. Most cars are going to have some variation in oil pressure as the temperature goes up and down. Oil viscosity has a big effect on how much pressure the pump creates. As long as it stays reasonably close to the middle, it's fine. Ford actually did something about other engines that had fluctuating oil pressure. On the 4.2L F-150 I believe it is, there is an oil pressure gauge in the dash, controlled by a pressure switch, not a pressure transducer! In other words, whatever the oil pressure, as long as it's sufficient, the needle stays right smack in the middle of the gauge. Saves a lot of those warranty calls from worried owners!
