My 94 has 72000 miles on it and when cold it will idle with 70-80psi. When warm 180F and driving at about 50 and 1500rpms it will be at 60-70psi. On the hotest day in traffic it will never see lower that 40-45psi. drivng 80 mph for 6 and half hours to bonnefest it never got lower than 50-60psi. I hope that helps.

170K, and I've never seen it below the straight up and down line. No, I don't have any idea how many psi that is... But I think it'* pretty good for this Texas heat, 102F today when I went for lunch.

EDIT: I actually read the guage.... It sits at about 75-80 all the time, 65ish when hot, and I mean Texas hot. (it was 112 in the sun today)

BlueEyes, -and Jr's3800, I was also thinking that it sounds most likely to be a flakey sending unit.
To show you how old and hard-headed I am, whenever I am suspicious of an oil pressure reading, I "T" in a good name brand mechanical gauge into the system. Then I can compare to the factory/electric unit. For what it'* worth, I have owned a lot of GM vehicles, and some of them had very accurate factory gauges. But others were really bad -like totally a joke. -and sometimes even inconsistent readings.

So probably the best thing to do in your case is to replace the sending unit, and then see what your readings are. (assuming you don't want all the hassle of adding a good set of Auto Meter (not AutoGage)-or other top name brand 270 sweep mechanical racing dials ,,,,probably not practical).

I'll have to admit that I have installed a lot of fairly expensive gauges in my "daily drivers" through the years, and everything would have been just fine and dandy without them. But at least I drove a lot of "worry free" miles, knowing exactly what the most important engine measurements were.

Also, I'd not be too worried about the oil filter. I know a lot of people will absolutely swear by one particular brand, or another. But some of the facts are, that all the common brands out there will meet the industry standard of about 18 to 20 microns. (personally, I like using the best quality I can find, and that is usually WIX. -as a side note, the NAPA "Gold" line of oil filters has been WIX for a long time now. -darn sure can't go wrong there)

But like I always like to admit to people: Use whatever brands you want, and everything will be just fine as long as you change often enough. As much as we would sometimes like to believe that there is some kind of real super dooper magic "automotive snake oils and other products" out there, when the chips are down and the race is run, they all come out pretty much equal. (by the way, for the past 20 years, I have ALWAYS used fully synthetic oil in every engine I own, and have never been sorry) The synthetic fluids do offer several "slight advantages", and are especially nice here for the winters in Northern Wyoming. I believe they would also have an advantage in very hot weather climates.

Oh Yeah, and about the ideas of oil pressure being affected by various oil filters,,,,, to that I have to say, "NO WAY JOSE" You would have to have some mighty bizzar/extremely serious other issues going on for pressure to ever be affected by the filter.

Yes, I have to agree, all the way around, except for how a filter can affect the oil pressure. Please express your theory on how that would be possible.

Hey, about the Fram filter using cardboard ends glued to the pleated media,, Isn't that totally disgusting !! At least most of the other brands use tin end plates glued to the media.

As much as it hurts to say this, I have cut apart "a mountain of filters" through the years, removed the end caps, stretched out the pleated paper, and hung them up to drip-dry. And when inspecting them for how much debris they had trapped, every one of them seemed very equal. (-of course, I'm sure that the better quality of media is trapping more of the particles too small for the eye to see.) And some filters use more square inches of medial than others.

Also, I always use the longer (one quart) sized filters, instead of that little pint-sized guy. The longer filter has at least twice the square inches of media, and will filter a much larger percentage of the oil sooner while the oil is warming up.

And isn't it something to think about, how much of the total oil flow volume is not even going through the filter until the oil gets up to operating temperature !! -especially bad in clold climates. The average person (probably 999 people out of 1000) doesn't even realize that fact.

Good discussions, -good for the brain !!
Thanks for the responses !!

This filter cartridge has a small outside diameter with a rather low filter element surface area (193 sqin), and features cardboard end caps that are glued in place. The rubber anti-drainback valve seals the rough metal backplate to the cardboard end cap and easily leaks, causing dirty oil to drain back into the pan. If you have a noisy valve train at startup, this filter is likely the cause. The bypass valves are plastic and are sometimes not molded correctly, which allows them to leak. The backplate has smaller and fewer oil inlet holes, which may restrict flow.

Will the larger PF-52 by AC provide higher PSI? How much more oil should be dropped in when switching to the PF-52? I'm considering doing it on this next change (namely since we have an old one sitting around no one ever used.

It says its' for a 2.2 as well...

BonneMeMN, the size of your filter will in no way affect your oil pressure.

I have about a dozen new filters of all brands disected at my home garage, and I shall take a look at the hole sizes tonight. -interesting point.

TrueWildMan, -or anyone else- I shall check the shop manuals tonight, but maybe you know off hand, with these 3800'* at what point in the lube path is the pressure sending unit located? Is it before, or after the filter?

Tnanks, Harry

Hmm...good question. It may differ between series I and series II. DrJay would know for sure for the Series I.

( darn I just finshed a reply, and lost the whole thing before submitting. -here goes again. )
Okay, this thread has given me the opportunity to do some homework, and I will present what I have found. My sources include the 1999 GM Shop Service Manual, H-platfrom, volume 1of2, #GMP/99-H-1, and some very very basic laws of fluid dynamics. Also, I so much enjoy the priviledge of being able to enjoy these forums, and NEVER wish to present any incorrect, misleading, or offending material. It is so nice to have this forum to share information. Thanks to all who make it possible

Section 6-170 of the manual even has a diagram, along with the "lubrication description." Some of the data there, and in other portions of section 6 are: The gerotor-style pump in the engine front housing discharges into the oil filter adapter assembly, which includes the spring & cylinder design pressure regulator valve, (designed to produce 60 psi at 1850 rpm, 10-30 oil, normal operating temp), filter bypass valve (approx 10 psi), and nipple to mount the full flow filter. If the filter should become restricted, full pressure and volume will still be delivered to the oil galleries.

So by now, a couple of myths should have dissolved:
-no matter how restrictive the filter, full pressure and flow will exist.
-it doesn't really matter which side of the filter the sending unit is, the pressure will be the same.

Pressure reading will be determined by many factors, including pump volume/wear, engine bearing clearances(wear), engine rpm, temperature, oil viscosity, and CERTAINLY by the accuracy of the sending unit and gage. But not filter type, size, brand, etc. Also, once the pressure regulator valve has opened, the pressure will be pretty much stabilized at that point.

Hey, also I got out my collection of dissected filters, and will happily pass along that data too, it anyone is interested. It was really quite a fun and educational project. -just a quick note, the Fram (and Pennzoil, and Quakerstate) do have slightly smaller inlet holes, but use 8 holes instead of the usual 6 or 7. When you think about it, that will distribute the oil a little more evenly around the media, as if that makes any difference at all.

So, anyway "there you have it." More to follow, if you desire !!
Enjoy

mm...Here'* my .02

Even before my rebuild I've noticed differences in presure from one filter to the other. I think it might have to do with how free flowing the element is inside it but thats just a thought. The main difference I noticed just by using a different filter is what is described, at idle it would drop down further (or less) depending on the filter. I can't recall which ones performed in what manner but I'm very sure thats what happened.

The pressure sensor: If you look at the housing the filter screws into and go about 5" above the filter till you see the bolts that hold the mounting to your engine you'll notice a long sensor that looks somewhat like a pocket sized flashlight mounted in the same housing, that'll be your sensor.

An interesting trick some people do is by stretching the oil pressure relief valve. If you pull that housing the sensor (and filter) are plugged into a spring and metal plunger will come out. Thats your OPR valve, carefully pulling on the spring until its 1-2mm longer and replacing it should give you a boost in oil pressure if all else is good.