Oil Pressure Guage Fluctuation

[wildbillrn]

Hellow Everyone,

Am AF newbie. Have 2005 Trailblazer EXT 4WD w/ 4.2L i-6. with 45,500 miles. Have noticed that oil pressure iguage reads 40 at no load idle (~5,500 to 6,500 rpm) and increases to just under 60 at highway speeds of 55-70 mph in 2 wheel hi. Is this normal or a little high? Does the oil pressure in the 4.2 i-6 fluctuate that much? Do I need to do an oil pressure check test with a mechanical guage? Have had one instance of engine light and oil light on ~39,500 miles. Was ~2qts low fo rno obvious reasons. Topped off with 2 qts, lights went out and this is when I noticed the pressure fluctuation. Appreciate any insights.

Bill

[maxwedge]

Oil consumption assuming no leaks is about 4-5k per qt. The gage readings are normal 35-40 at idle, 55 or so at speed, why do you think this is a problem? Low/ high reading variation applies to any engine.

[jdmccright]

40-55 psi is typical pressure range so no worries there. You don't mention when the last oil change was, so it's difficult to gauge your oil consumption as normal or excessive. But judging from my own experiences, you shouldn't be going through more than a qt or so per change interval at the odometer miles you have on that truck. Your rpms you list at idle look waay too high...should be in the 750-800 rpm. This could be a problem with your instrument cluster having bad servo motors for the needles. Any other symptoms to speak of? Rough cold idle? Hard start? Missing? More clues always help the diagnosis. Good luck!

[wildbillrn]

Thanks maxwedge and jdmccright. Both your answers providing something new to check out as well as some peace of mind. My mechanic of 20+ years sold his garage and I don't like the new owner, has a long rep for giving people the $haft.