When driving this morning I noticed that my oil pressure gauge was at 10 when driving on highway and then after a few minutes it would go back to 40 then drop back down to 10. What's causing this and where should I start. Please help.!!!!
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i would get a hold of a test gauge and test the pressure at idle, if it fluctuates at an idle you could either have a worn oil pump, or it might be the pressure bypass.

here is a tester at autozone
http://www.autozone.com/shop-and-gar...ressure-tester

here is one for napa
http://www.napaonline.com/napa/en/se...+pressure+test

here is one at advance auto
http://shop.advanceautoparts.com/web...hedFrom=header

 

How does the mechanical gauge work and where do I install it and what do I look for.

 

It screws into block where oil pressure sensor is now. Google for location images. Go to hardware store and buy a well pump pressure gauge for around $10. It needs to have threads of 1/8-NPT. Unscrew sensor and screw in gauge....it is that simple!

 

Agreed on checking with a mechanical gauge, only because the sending unit for the electric gauge can go bad or be inaccurate especially with age. Minimum oil pressure at hot idle is 13 psi. Should be between 37 and 75 psi at everything over 1600 rpms.

Also what kind of oil and filter are you running?

 

Been using 15-40 rotella t5 with wix bigger oil filter

 

Hmm so that shouldn't cause actual low oil pressure. How many miles are on it? Did it fluctuate between 10 and 40 all while driving on the highway or stop and go driving?

 

I just bought an 01 Cherokee with a 4.0 that fluctuates from 10-40psi. 10 at idle and increases relative to rpm and speed. Is this normal operation or indicative of a problem? Oil pump? Clogged screen?

 

Start a NEW thread. You will get more accurate replies and people responding won't have to toggle and reply between the two issues. IE: less confusion.

 

Generally answering everyone:

If the minimum oil pressure at hot idle is 13 psi and your at 10, yes that's a problem. With the caveat that the stock sender/gauge can be off with age, you have to verify with an actual mechanical gauge like those sold just about everywhere... parts stores, home depot, harbor freight, etc.

Lower oil pressure with age/high mileage is normal because bearings start to wear out. Yes the oil pump plays a part but a new pump won't fix worn bearings or a sludged up engine. Thin oil and a crappy filter will also cause low readings.

 

Gah! Those are expensive.

Harbor Freight carries a decent oil pressure test kit for $27, and it's eligible for the 20% off coupon to get it even cheaper. It has a 6' hose so you can drape it across the engine bay and read it from the driver's seat when you start it up. Mine works great.

http://www.harborfreight.com/engine-...kit-98949.html