So I changed the oil on my '99 Xj 4.0, which was running 40-50 psi for oil pressure. After I changed it it would not move the gauge past 20 psi, and sometimes falling to zero. After 5-10 min it comes up to 50 psi. I've read posts that say that sometimes the gauges or pessure sender acts goofy, but I just want some feedback to make sure. Sometimes I get in and it will jump right up to 50 psi, today (90 deg) it's all over the place. It isn't knocking or runing wierd. I put Valvoline Max Life 10w-30 (which I have ran since I've had it) in it and a (oversized) PureOne Oil Filter when I changed the oil. I have always ran Fram, so I swapped on a PH8 on to see if that changed anything. Nope. If it is overfilled on the dipstick, it will keep pressure constantly. I'm puzzled. I NEVER had an issue before I changed the oil.

 

my 89 never reads the same thing but the sender is covered in mud halve the time or under water i figure if the pump quits ill know it