<>300ZX - Low Oil Pressure. Dear Z Doc, . My '88 300ZX Non-turbo with 140,000 miles only shows about 40 psi on the dash oil pressure gage at highway speed, only about 20 psi at idle. I think in reality the pressure must be higher than that, otherwise I would have valve lifter noise at idle, which I don't. I know that these instruments have been notoriously inaccurate so I replaced the original sender with a borg-warner OEM quality sender. Still not much better. Thinking that the passage way to the sender may have gotten clogged with crud over the years, I started the engine with the sender out and the hole open. Lots of oil and crud came out but the reading didn't change much. What I would like to do is to install a simple mechanical gage, known to be accurate, into a "T" arrangement with the sender, but here's my problem: The port in the block next to the oil filter for the oil pressure sender is not a standard plumbing thread ( at least not in American fittings anyway). Do you know what size and thread pitch the port is and where I can locate appropriate fittings? Secondly, what is a reasonable oil pressure for this engine with this many miles.. Conventional wisdom says about 30 pi at idle and 50 - 60 at highway speed, but this is not a small-block Chevy. . Doc replies:. Hi Randall, Doc here... the thread is a BSP type that is very close to the standard pipe thread. You can run a "T" and install a manual gauge to see the pressure, but remember that the oil pressure line is close to the exhaust and the oil filter so careful routing is necessary and some type of heat shielding would be advised in the proximity of the exhaust. I don't have the factory Service Manual here at the house, but I would expect it to run at 60 PSI road speed and about 30 PSI idle. Also remember to carefully bleed the pressure line to the gauge after installing since air inside the tubing will compress and give an inaccurate reading. I hope that this helps you............ Are you a ZONC MEMBER? JOIN ZONC! Z OWNERS OF NORTHERN CALIFORNIA Send a FAX # and I'll get a membership application right out to you!. ZDOC OUT.