OPS was leaking, so I decided to replace. Old showed about 60 pounds until the car warmed up, then showed 45-50 or so at hwy speed once warm, 30-35 or so at idle. New sender shows 30ish at idle, and 45-50 warm, but never shows 60 at startup. I've heard of new senders showing higher pressure, but not lower. Would a leak cause an inaccurate high reading, or was the thing just old and screwed up leak or not? I'm pretty sure I got it screwed in at least as far as the old one was. 45-50 is pretty good pressure I guess for original motor with 158k, but I'd rather see 55.....

 

Sounds like the new one is reading correctly.

 

So what does 45-50 say about engine health? What would it be on a brand new engine like mine? (L98)

 

45-ish hot. Stock oil pressure in the L98 was with a stock volume oil pump (obviously) and a 40 PSI spring. You'll see more when the oil is cold, but not like 25 PSI more. And it's not like the gagues themselves were super-accurate. If you're in the middle of the range, you've probably got plenty of oil pressure.

More telling is that you have plenty of pressure hot at idle. That's where it'll drop off the most if you have mechanical issues with the engine.

If you want to see if the gauge will go full-sweep, find the sending wire in the 3-pin OPSI connector and ground it. Gauge should go full sweep to the top of its range. Don't mess this up- one of the three connectors is battery-hot (as in hot ALL the time) since it's the backup power path for the fuel pump, and you don't want to ground that!

 

Ok, good, sounds like I'm in good shape for now. It goes up to about 50 when its at cold startup, then drops to 45 when warm (instead of 60-45 with the old sender) I'm at 30-35 at idle, so that sounds good too. What causes a drop in pressure in a ragged out motor? Worn metal parts where the extra space in the tolerances keeps good pressure from building?

 

Yes. Tolerances open up and the oil has more room to squeeze out the sides of the bearing gaps. The oil pump usually has enough volume to keep up at higher speeds, but at idle when it's turning much slower, it can't keep up and the pressure starts dropping off dramatically.