what does good oil pressure mean?

[semaj281]

What is the acceptable range for "good" oil pressure?
I've always seen the 10psi per 1000rpm rule, but then again I've seen a lot of cars getting 40+psi at hot idle.
My Mustang idles at about 850 rpm, so that would mean 8.5psi is ok, but that seems low?

 

[XS650]

Originally Posted By: semaj281
What is the acceptable range for "good" oil pressure?
I've always seen the 10psi per 1000rpm rule, but then again I've seen a lot of cars getting 40+psi at hot idle.
My Mustang idles at about 850 rpm, so that would mean 8.5psi is ok, but that seems low?


The 10/1000 is a crude rule of thumb. Find out what your engine manufacturer recommends.

8.5 at idle does sound low. Are you using an accurate gauge.

 

[Mustang Man]

I really wish Ford would use an actual oil pressure gauge instead of an idiot light with a needle. I am debating about getting an aftermarket oil pressure gauge for mine.

I am thinking at 2000 RPM it is 60-65. I would bet at idle it is close to 35-40.

 

[Quest]

LOL! Out in this rather "dummbed" down consumer market, not many joes can decipher what an oil pressure gauge sez, letting alone the meaning of the reading (say, what?! 25psi?!?)

So, naturally, car manufacturers have to come out with some form of idea to give the dummb joes a way to differentiate between "I have some oil pressure" vs "I have no oil in my crankcase and the rod/main bearings are on the countdown mode".

Don't blame the car manufacturers for this, blame it on the joes.

 

[semaj281]

Just to clear things up, the 8.5psi that I threw out isn't my actual pressure. I was just applying the rule to my car which has no pressure gauge.

 

[jazeo]

Very rarely will you see a specific oil pressure range that is acceptable at idle, what you will see in a repair manual is a range at 2000 rpm. Depending on what engine you'll see something like 40-60 @2000. It does differ (a lot) depending on you make and engine.

With my old sbc, anything above 18 at idle is fine and 40-60 going the down the road is okay. The idle oil pressure increases with thicker oil and everything else seems to stay the same (when hot).

 

[eljefino]

If you look at the dummy light sender it's usually 4 psi. Usually why the light tells you your motor just cooked.

 

[TallPaul]

The Ford oil pressure specs (at least for the pushrod engines of about 10 years ago) typically ran 40-60 psi hot at 2000 rpm, or something like that. They did not give an idle spec. the 10 psi per 1000 rpm is a ball park thing and of course the relief valve will put an upper limit, but I would not apply that rule to idle. My F150 has about 15 psi at idle when good and hot. My motorhome will idle around 25 psi. Idiot light switches were set to light up when pressure dropped below about 8-10 psi, a bare minimum I would think.

 

[440Magnum]

Originally Posted By: semaj281
What is the acceptable range for "good" oil pressure?
I've always seen the 10psi per 1000rpm rule, but then again I've seen a lot of cars getting 40+psi at hot idle.
My Mustang idles at about 850 rpm, so that would mean 8.5psi is ok, but that seems low?


It can vary a lot with engine tolerances, especially with factory standard volume oil pumps that put out more or less the minimum flow needed (extra flow steals power and lowers efficiency, so the factory doesn't use HV pumps except in performance-oriented engines).

I have two essentially identical Jeep 4.0 engines (OK, the 01 has distributorless ignition, but they're still basically identical when it comes to heavy internal parts). The 99 has 140k miles and idles with about 25-30 PSI when its been run hard and is fully hot. The 01 has only 85k miles, but idles with about 12 PSI when hot. Neither has any odd noises, and both have good UOAs. Both run at around 40 PSI when they're hot at highway speed (~2000 RPM). My guess is that for whatever reason, the 01 simply has some larger oil clearances, either in the oil pump itself or in the bearings.

 

[meep]

and the pressures skyrocket when cold. I had an 86 escort (ugh) that idled at ~45 and pegged 100psi above 2000 rpm when it was cold out.

97 2.2L legacy (warm) idled at 20 psi and cruised at 60psi. It'd peg 100+psi cold at cruise.

agreed- 40-60 at 2k rpm is what i've seen in my SB chevys and jeeps.

Marine 350's tell quite a tale with oil pressures. cold vs hot the pressures change dramatically, and the pressure drops noticeably as the oil ages. Idling at 15 or cruising at 40 or below, CHANGE!

I want so badly to install an OP gauge in my jeep (along with atf temp), but there is no convenient dash space... I'll make some in time.

 

[Gene K]

On a Small Block Chevy we used to shoot for 20 psi idle and 60 psi max. However many newer versions of the lo-po motors like a standard 1980s LG4 305 came with a 45 psi relief spring to improve fuel mileage.

Your 2008 4.6L 3V has a special oil pump to run the CVT. I dont know how that plays into pressures. Maybe one of the Ford Techs can tell you what the shop manual says.

 

[mechtech2]

Lots of good advice above.
At idle, the demands are different because of no load.
And if you DO give it the gas, there is very little power down there. So not much pressure is needed or wanted.
Man oh man, cars sure vary about this, but 15-70 is a general range .

 

[semaj281]

edit: never mind.

 

[CATERHAM]

The 10 psi per 1,000 rpm rule is a good conservative guide, I don't know of any auto engine that requires more than that.

8.5 psi on idle sounds about right to me. The minimum spec's for my 328 BMW are 7 psi on idle (600 rpm) and 59 psi at "elevated rev's"; car has a 6,500 rpm red line.
Having said that I've never seen oil pressure less than 20 psi on idle and 70 psi at red line and that's with a 20wt oil, but the oil doesn't often get above 90C.

I have oil pressure gauges in all my cars and plus an oil temp gauge in a couple and I'd be lost without them. They provide a wealth of information on your engine and the selection and condition of your motor oil.

Forget regular UOA's, and install a dual oil pressure/temp gauge; it's a much better investment for motor heads.