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2001 Jeep GC with almost 180k miles. Change oil religiously at 3k miles. Always put in STP. Engine has been fantastic. Lots of pep but towing is suffering slightly. Gas milage is great. 19-21mpg on the highway. If I can draft, up to 26. Recently I've noticed the oil pressure hovers around 60 when on the highway. Usually it was around 50 +/-. I use Castrol High Mileage Oil. Should I be concerned?  

you did not say which motor you have...

the 4.0 straight six motors have been known to have a solidified slug of motor oil in the oil galley behind the oil pressure pressure sender down below where the distributer is...  there is no oil flow in the oil galley behind the oil sending unit.. so the oil in there can get hard... when pressure behind it builds up.. it can shove against the tiny opening in the sending unit creating a false LOW or a false high..

what is normally done..    disable the ignition system..  and verify that the engine will not start...  

place an oil drain under the motor.  on the passenger side of the motor actually...   using a oil pressure sending unit socket that fits.. there are 3 or 4 different depths ..  and some oil sending units only need a wrench..

take the sending unit out...    have somebody crank the engine for 10 to 15 seconds while you are watching the oil flow...

look for the plug or clot of oil that will come out..

after it comes out.. install a new oil pressure sending unit..

clean the area off with some brake cleaner spray..

CHECK the engine oil level...  bring it back to full.. you probably won't loose more than a 8 or 10 ounces..

this has a really good chance of taking care of the problem..

you might also want to check the ground cables...

there is one on each side of the engines right at the transmission bell housing area...

if you have a bad ground..   since there is ONLY ONE of the three wires to the oil pressure switch connected to the gauge.. with a bad ground between the engine and the body.. the gauge can be inaccurate...

i have a 2 minute test for the ground system.. if you have a hand held digital volt meter...  

Oops 4.7 V8  

you might try the same procedure...

there are mechanical oil pressure testers... these are about 25 bucks..  but.. if you have a 3 wire oil pressure sender..  you will need to hook it back in with a TEE fitting while checking oil pressure.. as the outer two contacts need to be connected for the fuel pump to work..



you will also want put your digital volt meter to work.... this test takes about 2 minutes.

set digital volt meter to 20 volt DC scale...

start the engine and turn on the headlights..

1.  test between the positive and negative battery post...   14.1 to 14.8 volts is expected..

2.  test between the Negative battery post  and the engine block...   0.04 volts is expected..

3.  test between the Negative battery post and the body....                0.02 volts is expected.

4.  test between the engine block and the body....                               0.02 volts is expected.

if you get 0.00 on the last 3 tests...    change the meter setting to 2 volts DC scale.. and retest the last 3...

see if you get close to the 0.04 or 0.02 volts...

post your results...


just today.. i ran across a car that was charging at 15.5 volts for test 1...   test 2 was 0.04 test 3 and 4 were 1.4 volts..

the ground wire from the negative battery cable to the body had come loose...    the car owner had done a valve cover gasket and left the ground wire from the firewall to the valve cover bolt dangling..  when i fixed those two problems.. the voltage returned to 14.1... and the battery did not overcharge anymore..  he had just replaced the battery as the previous one was cooked with the over 15 volts charging voltage..

another chrysler mini van had a dirty ground cable under the battery tray.. was throwing all kind of check engine light codes...

took the cables off.. wire brushed the ring terminals..  wire brushed the studs...  wire brushed the back side of the nuts..

the PROBLEMS vanished..  without replacing hundreds of dollars in parts that the codes pointed towards..  found with a 2 minute voltage drop test...  engine running.. headlights on..