Oil pressure tells you when to change sythetic oil and regular oil too

[db4690]

@George_San_Jose1

Immediately after oil change, warm engine, 55 psi. 50 psi before oil change.

50psi is pretty darn good, imo

50psi wouldn’t make me think “time for an oil and filter service”

[George_San_Jose1]

I concur, 50 psi wouldn’t signal any alerts for me either. However 35 would get me looking at the dipstick straight away, and 25 definitely would cause big concerns…

[texases]

But that’s different than something to use for an oil change indicator.

[TheWonderful90s]

@George_San_Jose1

Yes. But only slightly. Immediately after oil change, warm engine, 55 psi. 50 psi before oil change.

It might be because the new oil is cooler than the old oil was in the warm engine after you changed it. Did you drive it around a bit and then come back at let it idle to test the pressure in the exact same way as the old oil?

@asemaster

f the oil pressure control system in the engine is maintaining oil pressure at, say, 45psi, regardless of RPM and temp,

Well then it wouldn’t work on that type of vehicle. If the oil pressure is high enough to have the bypass opened then slightly lower oil pressure can’t be used as an indication that the oil viscosity is failing.

@davesmopar

I use a mechanical oil pressure gauge on my muscle car and have never noticed a correlation between oil pressure before/after changing it, I only use Dino oil in it with a zinc additive…

You could be changing your oil soon enough so the oil viscosity is never getting to the point where it is failing. Also, your oil pressure gage may not be precise enough or your oil system maintains constant pressure.

[Nevada_545]

Some engine computers monitor oil pressure and temperature to verify that the correct viscosity engine oil is used. If oil pressure could be used as a reliable input for the maintenance computer, vehicle manufactures would take advantage of that data.

[TheWonderful90s]

@Nevada_545

If oil pressure could be used as a reliable input for the maintenance computer, vehicle manufactures would take advantage of that data.

It can’t because people may add oil of unknown viscosity between changes without the computer knowing about it.

[Mustangman]

@TheWonderful90s

It can’t because people may add oil of unknown viscosity

The algorithm can be designed to look for a new baseline when the service reminder is reset. Plus short and long term running averages of pressure profiles. Very do-able with software.

[George_San_Jose1]

I’d guess the reason my truck’s oil thins a bit with use is not so much b/c the oil is degrading, but that a little gasoline is getting into the sump during rich-warm-ups and diluting the oil. More of a problem w/carburetor-equipped engines than fuel-injected probably.

[texases]

Good point, George. Goes to the problem with trying to use oil pressure as a measure of oil life - it can be affected by LOTS of things. And why bother even thinking about this when using OLM, or miles, have been proven to work just fine.

[TheWonderful90s]

@texases

or miles, have been proven to work just fine.

Has the 20,000 miles guaranteed been proven to work just fine on your engine? Do you trust what is on the oil at Walmart, or any place that sells oil that says “synthetic” on the bottle?

[Barkydog]

Never figured out on my Trailblazer, after 200k miles Always read the same, came to find out it was just a calculated value, not actual oil pressure.

[texases]

@TheWonderful90s

Has the 20,000 miles guaranteed been proven to work just fine on your engine?

I’m obviously referring to factory specifications.

[Rod-Knox]

Poor crankcase ventilation causes oil to get black quickly after oil change.

[MikeInNH]

@Rod-Knox

Poor crankcase ventilation causes oil to get black quickly after oil change.

Or just use Arco’s Graphite oil from the 70’s. It comes black. Not clear at all.