Oil pressure note

About 2 months ago I replaced my idiot light cluster with a gauge cluster and all was hunkydory. Pressure ran from 15-80 psi with a K&N filter. Just changed it today and put a mopar filter on, drops to 15 but only goes up to 40lbs. Going to keep an eye on it.

Spec is min 13 psi at idle, 37 to 75 psi above 1600 RPM. In practice, I've never seen a Jeep engine that hit 75 psi. A very few might hit 60 or 65 when cold, but the max running pressure I've seen is typically about 50 to 55 psi at highway speeds (around 2200 to 2500 RPM.

If you were getting near 80 psi with a warm engine, the filter was restricting flow.

It stayed at 50lbs all the way down to jersey and back. Guess I'll get used to it but I plan on picking up a mobil-1 oil filter tomorrow while I'm down in allentown as well as a new K&N. Will try all three of them. Not liking this one bit...

Fram has come out with a new reuseable filter, called the Air Hog alittle cheaper than a K&N. Any body tried that yet?

Kind of always wondered why everyone is always concerned about having the highest oil pressure. As long as there is oil pressure that means the system is working... right? Higher oil pressure I would think would be caused by one or all of these things - restricted oil passages, high viscosity oil, high volume pump. Is having small restrictive oil passages a good thing? Is having a high viscosity oil good? (lower viscosity = less drag on rotating parts, therefore somewhat better MPG's) What good is the high volume pump if it is just increasing pressure and not really able to provide much more volume?
Wouldn't the ideal be to provide more flow than more pressure? Wouldn't having the oil at a higher pressure cause it to be at least a little hotter and therefore break down it's viscosity a bit quicker?
Just curious on everyones thoughts,
Mike B.

Dunno if higher pressure would cause more heat, but I am also sometimes baffled when I see people with better than average oil pressure posting urgent messages that their engines are about ready to explode due to lack of oiling.

Many years ago I drove a Chevy race car transporter (with car on board) from Connecticut to Maryland and back, a round trip of about 500 or 600 miles, and the oil pressure never went higher than 13 psi the entire trip. That's the specified MINIMUM for XJs at idle. If that's good enough to haul a load 500 miles (as well as continue to haul loads after I returned), I fail to understand why people are panicked by pressures that are well within the published specs for the engine.

In my case it's because since new I had idiot lights, did my oil and filter changes and all was good. Then two months ago I put in a gauge cluster and kind of settled on the oil pressure ranges that came up, 20 at idle, 70 cold-60 warm at running speeds. That was with a K&N on there, when I changed the oil and used a mopar filter I noticed that it took a bit longer for the oil pressure to build up on startup and it did not respond as quickly to rev changes. That got me thinking. So I will pickup a few Mobil filters this morning and change the filter out to see what happens. While I realize that the electrical sender generally won't respond as quickly as a mech oil pressure gauge the response time this weekend was just a bit strange to me...

my oil pressure is stellar until its all warmed up, where as long as the engine is above like 1600-2g the op will maintain 40-50. but if it idles it drops to approx 10psi. what do u guys thing bearings or pump/press. reg. bad?

Well, up until this happened to me I would have thought mains but if the Mopar filter is 'good' and I use it as a baseline then I would have to say the K&N was causing more pressure. Question is, is the pressure sender on the supply side of the filter or the side that feeds the engine ?? Never really thought about it before. Will try a Mobil-1, maybe a purolator and an AC/Delco and see what those do.
What filter are you using ???

I'm not 100% sure, but I think the sender is on the output side of the filter. A couple of months ago, I lost all pressure at the gage. I was freaking out as I just replaced the engine last summer. Anyway, as a test I replaced the Fram (I know) filter with another. Pressure came right back up. My conclusion is the Fram filter got dirty and rather than bypass the filter it just shut the flow down. Not going to use a Fram filter again!

I think if you've got a reasonable amount of pressure (13 Lbs at idle sounds okay), then all is good. That is interesting that there is that much difference between the two brands though.

RichP said:

Well, up until this happened to me I would have thought mains but if the Mopar filter is 'good' and I use it as a baseline then I would have to say the K&N was causing more pressure. Question is, is the pressure sender on the supply side of the filter or the side that feeds the engine ?? Never really thought about it before. Will try a Mobil-1, maybe a purolator and an AC/Delco and see what those do.
What filter are you using ???

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In the diagram I have the oil flows=pan>pump>filter>blockmain oil gallery to the mains then rods.Valve tappets recieve oil from the main gallery as well as cam bearings.
I GUESS the pressure port is after the filter.
The old Mopar HP books for the V8s suggested 10 psi for every 1000 rpm.
Wayne

Spudboy said:

I'm not 100% sure, but I think the sender is on the output side of the filter. A couple of months ago, I lost all pressure at the gage. I was freaking out as I just replaced the engine last summer. Anyway, as a test I replaced the Fram (I know) filter with another. Pressure came right back up. My conclusion is the Fram filter got dirty and rather than bypass the filter it just shut the flow down. Not going to use a Fram filter again!

I think if you've got a reasonable amount of pressure (13 Lbs at idle sounds okay), then all is good. That is interesting that there is that much difference between the two brands though.

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The oil pumps that are used in internal combustion engines were referred to in the Navy as IMO [I Move Oil] pumps, they will keep pumping and in the case of the hydraulic systems on submarines are capable of 5000+ PSI, what regulates them in that case are bypasses that open on the trash can sized accumlators [big spring loaded storage tanks] when they hit 5k lbs, the pumps keep pumping only now they are pumping back into the supply tank until somebody moves the fairwater planes, rudder or stern planes or all of them at once and starts draining the accumulators.
Those gear driven pumps are the same as the pumps in our engines and not that much bigger, I seem to remember 1 or 2gpm and are capable of incredible pressures [cut you in half if you walk by a pinhole leak]. The bypass in the 4.0 and the 2.5L are set to 75LBS per the FSM's for both and that includes TJ's too.
I wonder if the synthetic material that Mobil and K&N toute in their filter construction flows more oil faster which results in quicker sender responses than the paper Mopars, Frams and others. I also wonder if the slower paper filters cause the bypass to cycle quickly so that you end up with an 'average' pressure but because the bypass is cycling so quickly the electric sender can't keep up or the gauge might have too much dampning... Don't mind me, I'm just thinking with my fingers....

CLb33fyXJ said:

my oil pressure is stellar until its all warmed up, where as long as the engine is above like 1600-2g the op will maintain 40-50. but if it idles it drops to approx 10psi. what do u guys thing bearings or pump/press. reg. bad?

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"Approximately" meaning on which side of 10 psi? Slightly above, or slightly below?

As I posted above, the factory spec is 13 psi at idle, which is "approximately" 10 psi. There's no load on the bearings at idle. As long as you have 40+ psi at road speed I don't think you have any cause for concern.