OT as it refers to the wife's '99 Jeep Grand Cherokee with the 4.0 IL6. Recently replaced the oil pressure sending at the engine block with a new Jeep part. It was reading low oil PSI so I knew that was the needed part to replace. Oil pressures looked OK after sender replacement for a few wks then now the oil press gauge is pegging! I checked the oil in the engine and it appears that one of the quick change oil placed has overfilled it by a quart? Could that make a big difference? Running at 80 PSI on the road and was running at 50 PSI which is normal for the motor. Electrical connector at sender looks intact. Any help greatly appreciated! Thanks!
Overfilling the oil causes the crank to "whip" the oil into foam, just like whip-cream. That causes low oil pressure. I'm guessing your new sending unit is defective.
Evan, I am in agreement with Darryl. I think you may have gottena bad sensor. "New in box" doesn't necessarily mean 'Good in Box" Good luck. Incidentally, that is the same engine that is in my daughter's cherokee with 195K on it. Still pumps around 45psi idle. good motor. :TU:
is it peged the hole time your jeep is running? or does it bleed down a little once it has warmed up a little
Yup, Whips the oil up, and aerates it. Air can be compressed. So I would expect erratic oil pressure. It also wreaks havoc with the hydraulic lifters making them noisy. The crank whips extra oil onto the cylinder walls. Too much for the oil rings to handle sometimes. Oil gets into the combustion chamber, causing detonation. Now that you've read all that, drain the extra oil out, it's not the best thing for the motor. If you really want to know the pressure, connect a good mechanical gauge, at least temporarily. Factory gauges are notoriously inaccurate.
Thanks everyone for the replies here. The sensor can only be installed one way so I don't think I could have messed up anything there! It will back off to about 65-70 PSI at idle then pegs when RPM's go up. It drops as it should when key off motor stopped. I can not find the receipt from the purchase but did find the box with the old sensor in it so at least I have the Jeep PN. Sure hope they have me in their system with the purchase? Wonder if they'll warranty an electrical part?? I will call them to see.....
was a defective sender Went to the Jeep place (surprised they were open today!) and they were able to look up the purchase in the system even though I couldn't find a receipt. Got the new sender on and oil pressures are where they should be again. The quote that was made "just because it's new in the box doesn't mean good in the box" was so true!! Thanks and the wife's happy again. I'll let her take the car back to the quick change oil place tomorrow so they can take out the extra quart of oil in the motor.
