Oil pressure concerns… (Page 1/2)
ninedriver JUN 07, 03:24 PM
I have an 88gt with 72,000 miles. Cold start oil pressure is approximately 50psi. After warm up under load it hovers around 40psi. However, at idle it drops to about 15psi. According to my tach, above about 2200 rpms the oil pressure is about 40 psi and at 1000rpms it’s about 15psi.
I’ve read numerous threads about main and crank bearing wear could be the culprit. I’ve installed a mechanical oil pressure gauge and it confirms the same readings. Thankfully, I have no bottom end noise or knock.
I’ve also read that you should have approximately 10psi per 1000rpm, however, I’ve never owned a car where I’ve seen the oil pressure drop that low at idle.
So, curious to know what everyone else is seeing as far as oil pressure readings and looking for suggestions going forward. I’ve mentally prepared myself for replacing the crank and main bearings but want to be sure before I take that on.
Thanks

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Steve

theogre JUN 07, 03:43 PM
GM Spec: V6, VIN-9, 30-45 PSIG at All RPM.
For Most regions use 5w-30 year round.
See my Cave, Oil and Filter

⚠️ Warning: Do Not Trust the dash/pod gauge!
Get a mech gauge and "install" on the engine.

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

Patrick JUN 07, 04:08 PM

What weight oil are you running?
olejoedad JUN 07, 04:14 PM
Those oil pressure readings are just fine.

Don't worry about it.
ninedriver JUN 07, 04:48 PM
Currently using 5w-30. Im definitely below the 30psi that ogre references as the lowest value. Again, I’m seeing 15psi, maybe a bit less. But maintains 40psi under load.
Patrick JUN 07, 05:01 PM

quote
Originally posted by ninedriver:

Currently using 5w-30. Im definitely below the 30psi that ogre references as the lowest value. Again, I’m seeing 15psi, maybe a bit less. But maintains 40psi under load.



Why not run 10w-40 if you're a bit concerned with lowish oil pressure? That's what I run in both my 2.5 and 2.8 Fieros.
ninedriver JUN 07, 06:56 PM
I thought about using 10w-30 (possibly 10w-40) but I’m concerned about masking a potential bigger problem.
Is this generally considered a good fix? And what kind of oil pressure gains should I expect?
Patrick JUN 07, 08:29 PM

quote
Originally posted by ninedriver:

I thought about using 10w-30 (possibly 10w-40) but I’m concerned about masking a potential bigger problem.



It's not like you have a need to run 75w-90 to make some oil pressure. If your engine has a bit of wear, using a slightly heavier oil is fine.

[This message has been edited by Patrick (edited 06-08-2022).]

armos JUN 13, 05:49 PM
Just to give you another number, many years ago I measured 22psi at hot idle on my V6. The off-brand sender was reading way lower than that - it seems the dodgy senders are in-line at higher readings but they drift off at the bottom of the scale. But if you used the mechanical gauge at hot idle (not just the high reading when cold), then you've already addressed this.

I haven't rechecked it since then, but it's been 10 years with no emergence of any problem. After switching to Delco senders the dash readings have stayed where expected.

I don't know exactly what oil I had in it at the time but I've generally used 10W-30, 10W-40, or 15W-40, or some mixture falling into that range, so a little thicker than what you have. Accounting for that, not sure how much difference would remain between our pressures.
Despite the labeling, 10W-30 tends to be a little thicker than 5W-30 even when hot, so just that may make some small difference. 10W40 would be a more meaningful difference though.

I get 60psi cold, which I believe is where a bypass valve opens. If you're not hitting bypass pressure under any conditions then that does sound abnormal.
But 15psi at idle doesn't sound critical, as long as it's coming up significantly when you put a load on it.

I don't know where they got the data from, but 60degreev6 quotes 30-55psi at 2000rpm, and just 10psi at 500rpm.
https://www.60degreev6.com/...gen-1-specifications
theogre JUN 13, 09:33 PM
GM and Most Others say a Range of Pressure at All RPM Because Oil Pump installed can generate More Even At Idle and have a Regulator to Limit Final Pressure.

Low Pressure is a Problem. Pump itself and other parts can wear out. Many drive w/ Low Pressure for years while others leave you stranded on the highway at worse time possible w/o other warnings. But you can believe the myths saying is "Normal."

Again, Do Not Trust the Dash Gauge.
Use a real gauge and other tools when dash says low or high of whatever.
Many things besides the sender can make dash gauges lie to you.


quote
Originally posted by armos:
I get 60psi cold, which I believe is where a bypass valve opens.

No. Bypass Valve, in Many GM is in the Engine where Filter Flange is, only open when input to and outlet from the Oil Filter is > ~ 7 PSI different.
Oil too thick to flow thru the filter, bad/drity filter media, and some other setups can open this valve but you don't want that open.
Not only does Dirty Oil get in the engine, Bypass valve often doesn't flow enough when have filter problems.

Example:


Filters With Bypass Valve work same but set point to activate it can above or below 7 PSI. Most are at the Top of the media and often harder to see. See https://www.youtube.com/watch?v=-Fy-G9t0jPs