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How much oil pressure is too much? Or, 0W40 + high volume oil pump = ?

4K views 14 replies 6 participants last post by  Ken Hennessy 
#1 ·
I've finally put about 1500 miles on my rebuilt-bottom-end LT1, which included a high-volume oil pump. (Not my choice--I would have probably stuck with standard volume and pressure.) Break-in oil was 30wt, which got changed out at about 30 miles. Next was 500ish miles of Pennzoil conventional 5W30, followed by 950ish miles also using Pennzoil 5W30, using an AC Delco PF52 filter (NOT the PF52E).

I have an F-body gauge cluster with the sensor harness modified to make the oil pressure gauge display actual oil pressure, not sit at 50psi or whatever. It reads 0psi and 80psi, with unmarked notches at 1/3 (20 psi?), 1/2 (40 psi?), and 3/4 (60 psi?).

With the 5W30, oil pressure would be about 65-70psi on cold start, run ~75psi during gentle cold warm-up driving, run ~40psi at idle while hot, and run ~60-65psi during hard acceleration when hot. Blackstone said that the 500ish mile sample tested out as low 30wt or high 20wt, so presumably the 950ish mile sample, which I just took tonight during the oil change, will also be slightly out of grade.

What I've noticed is that sometimes the oil pressure gauge will drop when I expect it to climb. Let's say, for example, I'm cruising along and oil pressure is at 55ish psi. Sometimes, when I accelerate briskly, as in 1/2 throttle or so and the car downshifts to second gear, I'll expect the oil pressure to climb to 60+psi, but the gauge will drop to 50ish psi during the acceleration. After I let off, gauge behavior returns to normal.

Tonight, I switched out the Pennzoil 5W30 for Mobil1 0W40 and a Mobil1 M201A oil filter. Since the LT1s are generally known for lowish oil pressure, and since in my Mustang Cobra, the Blackstone analyses look better running 0W40 instead of the factory-recommended 5W20, I have been running 0W40 in my Caprice and in my ~160K-mile bone-stock Roadmaster (which I know longer own). (Also, my wife's GL450 and my M5 both take 0W40, so it's convenient only having to stock a single brand and weight of oil.)

During a brief 10-minute test drive after letting the car idle a bit to warm up and circulate the new oil, I noticed that the oil pressure gauge seems to run 5-10psi higher than before. That's expected. I haven't seen cold start PSI as the engine was still warm when I did the oil change. But I did notice the oil pressure drop under acceleration more consistently--pretty much every time I'd get on it, compared only part of the time while running the 5W30.

My guess is that oil pressure is climbing beyond the oil filter's bypass range, and it's opening to let oil bypass the filter. I don't think that going back to 5W30 (Mobil1, not conventional oil, since break-in is done) will necessarily help, since the conventional 5W30 seemed to periodically activate the bypass, and since synthetic 5W30 is much-more likely to hold its viscosity over the duration of the planned 5K-mile oil run.

Is this something I need to be concerned about? Or should I not worry about it, since the filter's bypass opening (assuming that's what's happening) is keeping the oil pressure within an acceptable range?
 
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#2 ·
Did whoever rebuilt your bottom end and spec a HV oil pump advise what weight oil to use?

and are you confident the oil gauge you have reads "accurately"?

Beyond the oil pressure concerns....I would not go synthetic until well after 5k miles on a new motor......
 
#3 ·
Did whoever rebuilt your bottom end and spec a HV oil pump advise what weight oil to use?
and are you confident the oil gauge you have reads "accurately"?
Beyond the oil pressure concerns....I would not go synthetic until well after 5k miles on a new motor......
Nope, no advice from the engine builder about what weight of oil to run. He's the guy who took 7 months to do the job, rushed through the final reassembly, then tried to overcharge me, and then threatened to sue me.

Yes, the reading on the oil pressure gauge generally jive with what my experience tells me is correct.

5K miles? That sounds wildly way too long. Why? This is how I've always broken in new / rebuilt engines, including driving style and oil change intervals: Break In Secrets--How To Break In New Motorcycle and Car Engines For More Power
 
#4 ·
My guess is that oil pressure is climbing beyond the oil filter's bypass range
For what you invested in your motor I would be more worried. New built motors may have more stuff to filter than at any other time in a engine's life. If you are bypassing this stuff is working it's way around the motor. Not good.

I would start with a mechanical gauge to see if the measurement is real. At the least unless you personalty purchased the gauge sensor for the same model/year/engine as the gauge I would consider replacing it to make sure it reads correctly.

I too would guess it is bypassing from what you have reported. A long read through a oil filter data catalog might find a filter with a higher bypass pressure.
 
#6 ·
I've been doing some reading and neither the AC Delco PF52 nor the Mobil1 M1-201 have a relief bypass valve, so pressure drop would be coming from something else. I recall reading that the oil pump itself has a pressure relief valve, so presumably that's opening to bleed off some pressure. I'll read further to confirm, but in the meantime, I think it's fine as-is.

https://shop.advanceautoparts.com/p...rmance-oil-filter-m1-201/3730006-P#fragment-2

http://www.oreillyauto.com/site/c/detail/ACD4/PF52.oap?ck=Search_pf52_-1_-1&keyword=pf52
 
#7 ·
I would never rely on those glorified "idiot" lights for accurate info. Your true oil pressure could be anything. I recommend "real" gauges,or you may as well be flipping a coin.
 
#9 ·
I bought an oil pressure sensor (replaces the stock oil pressure switch) and had the resistor added to the wiring to make the gauge display actual pressure as read by the sensor. It may not be an enthusiast-grade standalone gauge, but based on my research and my personal experience, I have no reason to suspect that it is inaccurate.
 
#8 · (Edited)
#11 ·
How much money you've got tied up in this motor,and refuse to invest in an actual gauge. Preferring to rely on the factory electric B/S gauge that (you hope) is somewhat accurate? Naturally it reads where oil pressure is about the lowest. Not at pump output,or even pressure in the cooler lines. Either one of which would be a more dependable,and accurate source...
 
#12 ·
Guys, while I appreciate the concern, I'll be blunt--I'm just gonna assume that the oiling system is performing sufficiently and not worry about it.

My original concern was that too much oil pressure would cause the filter to go into bypass mode and periodically not filter the oil. I've since discovered that there is no pressure relief bypass in the filter, and that excess oil pressure is bled off by a spring-loaded valve at the oil pump itself, with excess oil being dumped back into the pan.

From what I've read, the oil pump pressure relief spring takes effect between 65-75 psi, which jives with what I've observed on my gauge--under conditions when oil pressure is likely to be in that range, the oil pressure gauge will sometimes dip into the upper-50-psi range. I get that a professional-quality gauge would be provide more confidence in its accuracy.

I'm also going to assume that the engine builder set bearing clearances to work with a high-volume oil pump. Despite his short-cutting the last 15% of the job, I did personally see him spending a fair amount of time confirming bearing clearances with Plastigauge and doing other detail-oriented stuff like setting ring gap. If the builder didn't set the clearances to compensate for a high-volume oil pump, well, too bad for me, pretty much. I'm not going to tear into the motor to replace the oil pump or change out bearings. So rather than worry about something I don't have the ability to change, I'm just going to assume that it's good.

I am also sending oil off to Blackstone for analyses. For the first two oil changes, there haven't been any red flags (or even yellow flags), which also helps me rest easier. I'll post them up here once I remove my personal info from them.

Still, thanks to everyone for their input.
 
#13 · (Edited)
Well....you were the one that asked the ?

assuming your version of oil gauge is accurate, lets step away from that discussion.

The spring in the oil pump dictates "pressure", the gear size (specific to the pump) dictates "volume"

This video explains:



If you have any 411 from your builder regarding measured bearing clearances and if he chamfered the oil hole faces on the journals that would be good more to confirm if you should be running a thicker weight oil if he did set the bearing clearances wider than stock

"if" your bearing clearances are as tight as stock a HV pump some feel puts higher stress on the oil pump drive gear. IDK if that is true but I understand the logic behind that thought.

If the details of your build are not available maybe 25k mi down the road if you ever have to re-seal the intake just remove that drive gear and look at it. Also if you find "fuzz" on the tip of a oil drain plug (magnetic tip) on each oil change you might want to pull the intake to see if the drive gear is wearing abnormally.

your Blackstone tests are also a way to monitor what is in your oil so if that all checks out....you should be fine

At this point it is whatever it is and you don't seem to be having any issues other than what you see on your "adapted" oil pressure gauge....again assuming that is accurate.

If this concern weighs on you not knowing, just get a external gauge you could temporally attach just above oil filter and compare that to your interior gauge...although it would require a helper reading the interior gauge while you monitor the temporary mechanical gauge to compare

You may find your interior gauge is not as accurate and giving you higher than what your oil pressure really is....or confirm your interior gauge is accurate........since your original ? is based on the assumption your interior gauge is accurate

If your gauge is in fact correct you would not want to run a thicker oil
 
#14 · (Edited)
Since everything appears to be normal or near normal for your pump and this is a new rebuild then there's a possibility that your oil pump pickup tube might be too close to the pan. Many a mediocre mechanic has been know to get the clearance too close to the pan bottom or just not checking it at all. If it is too close then it will perform normally when at low RPM but when you rev it the pickup tolerances may allow the oil pump to cavitate causing a drop in oil pressure. I've only seen this about three times in my 70+ years but I have seen it. The first one nearly drove me crazy but the pickup to oil pan bottom was about 1/8 inch. Apparently that's not enough. One of the clearances was non-existent and the pickup tube was resting on the pan. Oil pressure was fine up to about 3000 RMP but then it actually went down, a lot, at WOT. I know it's kinda hard to check but the pan will come off fairly easily and a good measurement or a glob of clay will let you know for sure.
 
#15 ·
Bypass valve

The oil pump and the oil filter adapter have bypass capability. The oil filter itself does not have bypass capability.
The part the oil filter screws on to has a bypass valve built into it. Some builders recommend plugging this bypass and then warn to warm up the engine before any high rpm work.
Did your builder use the stock oil filter adapter?

Ken Hennessy
 
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