idle oil pressure

[Airborne5.0]

Hi guys,

Ford manual states 10-15 PSI once warmed for a 2018 mustang. I recently over filled my oil by .5 quart and drained some out. Once warmed I idle at 17ish PSI. Is this an issue indicating excess oil in the system and I should drain some more?

Thanks for advice

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[GT Pony]

Oil pressure isn't effected by the oil level unless the oil is so low that the pump sucks air - then the oil pressure goes towards zero.

Check your oil level per the owner's manual. 17 PSI of oil pressure at hot level is fine, nothing to worry about.

 

[Airborne5.0]

Big roger, thanks! Oil level is good, although checking with the dipstick location is absolutely horrible.

 

[ORRadtech]

Oil pressure isn't effected by the oil level unless the oil is so low that the pump sucks air - then the oil pressure goes towards zero.

Check your oil level per the owner's manual. 17 PSI of oil pressure at hot level is fine, nothing to worry about.

While that's mostly true it doesn't really tell the full story.
An engine that is 2 quarts or more low can have good oil pressure, an engine that is over filled can have good pressure as well.
The problem comes in at the extremes. So little oil that the sump can't fill quickly enough can cause low oil pressure from sucking air but too much oil, to the point that the crank can touch it, causes the oil to foam. If the pump tries to pump foam you will lose oil pressure then as well.

 

[Cobra Jet]

Oil PSI will change or "peg" based on multiple conditions.

High oil psi upon initial startup is normal in every vehicle. The oil viscosity is thicker due to it sitting and dependent upon exterior seasonal temps (whether in a a garage or not). The colder the engine block, the thicker the oil will be, then as it warms up viscosity changes (thins out).

Oil PSI in ANY engine is always dependent upon operating temps, oil viscosity and RPM.

The oil psi specs below is for a bone stock S550 Coyote 5.0 right from Ford:

That PSI info is also based upon the standard recommended oil for the 5.0 Coyote.


—-
Here was an older thread regarding oil psi:
https://www.mustang6g.com/forums/threads/2018-mustang-gt-15-psi-oil-pressure-normal.109015/


IMO, Ford should have designed the oil psi gauge with better increments.

 

[GT Pony]

While that's mostly true it doesn't really tell the full story.
An engine that is 2 quarts or more low can have good oil pressure, an engine that is over filled can have good pressure as well.
The problem comes in at the extremes. So little oil that the sump can't fill quickly enough can cause low oil pressure from sucking air but too much oil, to the point that the crank can touch it, causes the oil to foam. If the pump tries to pump foam you will lose oil pressure then as well.

That's basically what I said - which was: "Oil pressure isn't effected by the oil level unless the oil is so low that the pump sucks air". Oil pressure will be normal until the level in the sump gets too low and the pump isn't sucking oil.

The oil level would have to be extremely over-filled to get the crankshaft to foam it up, and the foaming would have to be very extreme to see an effect on oil pressure. The OP thought his oil pressure might have been too high from a slightly over-filled oil level ... but obviously that wasn't the reason why he saw 17 PSI at hot idle. He saw that because that's what his car does with the oil he's running at what the hot viscosity of the oil was at that point in time when he looked at the oil pressure gauge.

 

[KingKona]

Hi guys,

Ford manual states 10-15 PSI once warmed for a 2018 mustang. I recently over filled my oil by .5 quart and drained some out. Once warmed I idle at 17ish PSI. Is this an issue indicating excess oil in the system and I should drain some more?

Thanks for advice

No, it's not. It's fine.

Wondering how you over-filled by 1/2 a quart?

 

[Airborne5.0]

No, it's not. It's fine.

Wondering how you over-filled by 1/2 a quart?

I am in Canada, we use liters here and I got 2x 5L jugs. 10 liters is 10.56 quarts. While doing my oil change I got my liters and quarts backwards. Used both jugs thinking they were quarts.

 

[KingKona]

I am in Canada, we use liters here and I got 2x 5L jugs. 10 liters is 10.56 quarts. While doing my oil change I got my liters and quarts backwards. Used both jugs thinking they were quarts.

Ho.

Lee.

Chit.

I was expecting a moronic answer, and instead you blew my mind.

 

[Airborne5.0]

Haha!

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