I've got the high flow Melling oil pump on my 280 and it shows 3/4's on start up then 1/4 when hot at idle then back to 3/4's while driving.

Before I noticed this issue, it showed about 1/2 up the meter pretty much always. I think that's like 45 lbs/in2. It was pretty constant, and got there quickly after start up, whether it was driven or idled and regardless of tempurature.

sender...try a new one

Haynes specifies a "full flow" oil filter that should not be tightened more than hand-tight, printed in italics for emphasis. I used to tighten it more than that. Not sure how over-tightening the filter might affect pressure but I'm wondering if this is yet another reason why I was reading too low. Just based on experience the regular FRAM filters seem to be crap when (if?) my pressure was so low and the oil got dirty way too quickly. I have an XG filter from FRAM I was going to install at next oil change which are allegedly very good quality (not available in auto-parts stores around here I've been to though), but I'll take a look at NAPA Golds (or K&N) which people seem to like. Thanks for the warning FastWoman I'm really curious now how a different brand oil filter might affect what my gauge reads. x

Maybe they say not to over-tighten it because they can be hard to get off. And the crappier ones have really thin metal so if you use an oil filter wrench it will twist up like a churro and spill oil all over the place.

I'm using Fram to, we mostly get those here. I did tighten with hand, but had to re-tighten with hand several times, because it came loose, due vibrations of the engine block I think, but now it seems to hold, after a few re-tightening.