My second disco an 04 with 112k miles has me stumped. After sitting over night it takes 3-4 seconds for the oil light to go off then the oil pressure gauge bounces 40-50 psi then stabilizes. ive tried 2 different gauges and the same result. oil pump looked liked new when i did the head gaskets and timing chain. 2k hot 50spi. 11 psi hot idle but it goes from 11 to 0 then backup. I have tried all the usual filters and its running 20/50. My 03 same gauge (bosch)does not do any of this and it has 162k with worn cam shaft. Both discos have new big end bearings. All i can think of is the relief valve but it wont come out.. Any ides fellas?

 

Has this engine always done this? If you have 50 psi at 2k, then the relief valve is prob ok. Have you checked the o-ring where the pick up to be meets the block? If it were bad (or missing) that might allow oil to drain back into the pan overnight causing the 2-3 sec oil light on startup. I haven’t had the pan off personally so just guessing.

 

Its been wonky since i got it in January. Just installed new land rover o ring yesterday. more than likely just going to change pump assy but wanted to see if any one else has ever encountered this. Not sure how a pump that looks nearly prefect could be causing this issue.

 

One of three things, walked cam bearings, broken oil pump gears, or upside down rocker shafts. You don't have oil pressure at low rpm because the oil output is close to equal to the bleed from the various areas - rocker shafts, cam bearings, main bearings. You said it had new main bearings so it has to be either low oil output or high bleed rate.