Oil Pressue Concern

[rslifkin]

I finally got around to installing a real oil pressure gauge in the Jeep to supplement the terribly inaccurate factory one. However, I've noticed something concerning. With the engine hot, the pressures seem a bit low across the board. With 5W-40 in the sump, I'm seeing 10psi at hot idle (not concerned about that), about 20psi cruising at 1500 rpm and 30psi by 2000 rpm. However, even if I wind it up to 5k rpm, the pressure never gets above 35, which makes me think that I've either got a worn oil pump or clogged pickup.

I'll be able to get cold pressures tomorrow once the Jeep has sat overnight, as I finished the gauge hookup after it was already warm.

Thoughts? The gauge is a VDO electric one, FWIW.

 

[94astro]

Don't know what oil you are using, is it synthetic? When I went to Mobil1 Advanced synthetic 10w-30 my oil pressure drop to 20# at idle & 40# at cruise, that has been a few months ago & nothing has changed so I quit worrying & chalked it up to better flow & less pressure.

 

[rslifkin]

Yeah, it's Rotella T6 synth. The factory gauge behaves exactly the same as it has since I got the Jeep, so it's quite possible that it's always been like this. It's just being so far under the 10psi per 1000 rpm rule that worries me a little, as 33 - 35 psi seems low for running at 5000 rpm.

 

[440Magnum]

I haven't put a real gauge on a Magnum version of the smallblock Mopar personally, but my prior-generation 318 factory oil pump/relief valve would never cross 40 PSI regardless of RPM. With a HV pump, I'd see 55-60 max. The small Mopars don't generate a ton of pressure, and as I mentioned in another thread I think all Mopars are more or less designed to reach their relief pressure at a moderately low RPM and stay at a generally constant pressure. I do remember another guy who had much lower pressure after retrofitting Magnum heads (and oil-thru-the-pushrods lifters) and finally decided it was just the way those engines run.

On the other hand the Magnums did have the leaky lower intake plenum issue and the gas leakage could cause gritty deposits in the oil that could eventually clog the pickup (I've seen THAT one personally). But by 98 that problem didn't happen nearly as often. Have you reworked the lower intake plenum to address that possibility?

Any odd noises or anything else concerning? Try a different oil filter and see if that makes a difference.

 

[JR]

I have 87 D150 318-2bbl/727torqlite 2x4 3.08rear.
wolfhead 10w-30 CF-rated syn-blend and partsmaster short filter.
warm idle is around 10psi. cruising speed around 25-30psi. hard eccell is 35psi maybe 40psi. i know it ain't a 5.9magnum but it might help.

i ran 5w-50 castrol for 10+k with one quart ford filter.
it gave the same pressure.

 

[wrcsixeight]

I have a rebuilt LA 318( pre magnum) I have no idea if the rebuilders installed a stock or a high volume high pressure or a stock pump

I have a mechanical Equus OP gauge

My OP relief valve when cold is apparently 68 PSI
My op relief valve when hot is 62 psi

With 0w-40 in the sump, at 550 rpm hot idle, I see 16 to 18 psi
When hot it reaches 62 psi at about 2200 rpm.

But there is around town hot, and at the first redlight after a longer highway cruise hot, where the pressures drop some more over what I listed above.

At 65mph I run 2k rpm, and see 45 to 55 PSI.

 

[rslifkin]

No odd noises, other than a bit of mild lifter clatter (it's had that since I got it, before and after the cam swap, new lifters, etc.). I did the plenum gasket shortly after I bought the Jeep (it was leaking just a little, not badly) and again the last time I had the heads off (wasn't leaking, but I wanted to do a little port work on the intake). It's got an upgraded aluminum plenum pan on it.

The filter is the standard short one, not enough clearance for the longer filter in the Jeep. It's currently a pureone, so I can certainly try something different at the next change to see if it changes anything.

It's quite possible that the relief valve just trips at pretty low pressure, as the max pressure I see is the same whether it's just warm or if I've been beating on it to get the oil good and hot (I've seen it as low as 8-9 at idle and 18 at 1500 rpm after beating on it).

I guess if small block Mopars are known for running fairly low pressure without issue, it's probably harmless.

EDIT: I just checked the service manual and the specs are minimum 6psi at hot idle, 30 - 80 psi at 3000 rpm.

 

[CurtisB]

There is a misconception that your oil pressure measures the flow of your oil circuit, although this is true to an extent, it mainly measures the pressure of your oil circuit. Just because an engine runs at a lower oil pressure does not mean that your parts are not oiling properly, the oil is just circulating with less resistance, and hence the perceived low oil pressure. At 35 psi, and given oil viscosity/bearing tolerances your engine has just reached its maximum system pressure.

 

[OVERKILL]

It is only the low-side for pressure but I wouldn't be insanely worried about it or anything. The factory spec minimum of 6psi is also probably with 10w-30, keep that in mind. You are near the minimum spec, which likely means worn bearings.

 

[rslifkin]

I just took it for a drive after sitting for a bit (lukewarm, coolant around 130* at the start of the drive) and it was holding about 35 psi at idle after I started it and about 40 while driving (up to 2200 rpm). It never went over 40, so I'm guessing the relief valve is just set at a pretty low pressure.

 

[rslifkin]

After thinking about it, next time I change the oil, I'm going to let a couple quarts of solvent sit in the oil pan for an hour or so (engine off, of course) to try to dissolve any gunk that might be on the pickup screen.

I'm also considering moving from T6 to the Castrol 5W-50 on my next change ($10 difference per change, so not a big deal), although it's a decent bit thicker at 40C, so I'm slightly concerned about how it might handle starting at low temps (down to about 0* F).

As-is, the T6 is thicker than the spec-ed 5w30 / 10W-30, so it's already a bit of extra protection despite the low pressure, but considering I do beat on the motor a lot, it probably wouldn't hurt to go up another grade (I wouldn't be surprised if I've gotten the oil hot enough to see 6 - 7 psi at idle when it's actually hot outside and I'm beating on it for sustained periods or towing, etc.)

 

[rslifkin]

Also, the Castrol 5W-50 is a consideration due to having a higher TBN than the T6 I'm currently running, which might (although I'd confirm with a UOA) allow me to stretch my 6k OCIs out to 7500 miles.

 

[440Magnum]

Doing some googling around, it becomes pretty clear that the Magnum series engines tend to run lower pressures than the pre-Magnums. I'm sure the oil-thru-lifter change is partly responsible- the old (shaft rocker) smallblocks got a shot of oil per bank, through the rocker shafts, every turn of the camshaft. The Magnum series dribbles oil through all 16 pushrods continuously, which vents more oil and reduces pressure..

 

[440Magnum]

PS, in stock form the biggest weakness of the 318/360 is oiling at sustained high rpm (6500+). The #3 and sometimes #4 main tends to starve because (so the old engine modding books say...) the flow speed down the main feed gallery (passenger side) becomes so fast that the inertia of the oil causes it to "miss the turn" into the #'s 3 and 4 main saddles feed tubes. The #5 main is protected because it has its own stub oil feed straight off the pump. The #1 and #2 get oil because the oil decelerates toward the front of the block where there's a flow obstruction and turn at the crossover gallery, and that raises pressure in their feed galleries.

It really only showed up in hard-raced 340 engines or modified 318/360's , because the stock 318 and 360 just don't make any power over 5k anyway because of the heads and valves. There are a number of documented ways to address it for hardcore racing (safe to well over 7000 RPM), the classic being to install a crossover tube in the lifter valley:

http://www.moparmusclemagazine.com/techarticles/engine/mopp_0201_building_beefy_blocks/photo_26.html

The crossover feeds the driver's side lifters right from the top of the oil pump feed, reducing the volume of oil that would otherwise have to race to the front of the block down the passenger's side gallery, then come back up the driver's side. That in turn raises the back-pressure in the passenger's side gallery, lowers the oil speed, and evens out the pressure at all the mains.

 

[rslifkin]

At least it seems like it's pretty normal, so I'm not too worried. It never exceeds 42psi cold, so the relief valve is definitely at a pretty low pressure.

 

[hattaresguy]

Its an old motor, you still exceed the required oil pressure according to the FSM so I wouldn't worry about it. Just run it.

Low oil pressure means your getting more oil flow anyway.

 

[440Magnum]

Originally Posted By: hattaresguy
Its an old motor, you still exceed the required oil pressure according to the FSM so I wouldn't worry about it. Just run it.

Low oil pressure means your getting more oil flow anyway.


Unless the cause were a worn-out oil pump, leaky pressure relief valve, clogged pickup screen, etc.

I think he's ruled those out and its just the nature of the beast... but there ARE plenty of cases where low pressure != "getting more oil flow anyway."

 

[rslifkin]

Originally Posted By: 440Magnum
Originally Posted By: hattaresguy
Its an old motor, you still exceed the required oil pressure according to the FSM so I wouldn't worry about it. Just run it.

Low oil pressure means your getting more oil flow anyway.


Unless the cause were a worn-out oil pump, leaky pressure relief valve, clogged pickup screen, etc.

I think he's ruled those out and its just the nature of the beast... but there ARE plenty of cases where low pressure != "getting more oil flow anyway."



It definitely could be an oil pump issue, although there does seem to be adequate flow (lifters don't get noisy at idle). At some point, I'll plan to drop the pan and change out the pump / pickup and see what happens.

 

[SteveSRT8]

Originally Posted By: rslifkin
I finally got around to installing a real oil pressure gauge in the Jeep to supplement the terribly inaccurate factory one. However, I've noticed something concerning. With the engine hot, the pressures seem a bit low across the board. With 5W-40 in the sump, I'm seeing 10psi at hot idle (not concerned about that), about 20psi cruising at 1500 rpm and 30psi by 2000 rpm. However, even if I wind it up to 5k rpm, the pressure never gets above 35, which makes me think that I've either got a worn oil pump or clogged pickup.

I'll be able to get cold pressures tomorrow once the Jeep has sat overnight, as I finished the gauge hookup after it was already warm.

Thoughts? The gauge is a VDO electric one, FWIW.


When you changed the cam was the timing gear set and chain done too? Many of my Mopar 318/360's in my fleet back in the day would puke bits of plastic that would clog the screen of the oil pickup. Oil pressure drop was obvious.

Note that low oil pressure does NOT indicate more flow every time, it can also be a serious problem...

 

[Clevy]

Originally Posted By: rslifkin
Yeah, it's Rotella T6 synth. The factory gauge behaves exactly the same as it has since I got the Jeep, so it's quite possible that it's always been like this. It's just being so far under the 10psi per 1000 rpm rule that worries me a little, as 33 - 35 psi seems low for running at 5000 rpm.


The 10psi/1000rpm is a small block Chevy rule. It may not be a requirement in respect to engines built by other manufacturers.
As far as your oil pressure is concerned I think its pretty close to what dodge required when new so just keep an eye on it and watch for anomalies.
If it makes you feel. Any better my hemi cruises on the highway at around 50 psi with 68000 miles so it might just be that big pressure isn't required in dodgeland.
The fact that even operating at elevated rpm it maxxes out at 42 is a very strong indicator that the relief valve is opening.
If it's not telling you with odd noises or providing clues with funny smells and oil condition then in all likely hood it's just how this engine runs.
I don't know if I'd go up a grade just yet though.
Evidently the pressure relief is at 42 psi and going thicker will likely get you to that pressure faster forcing a pressure relief event.
But if that's what you are after then give it a shot.