Low oil pressure on the highway?

F8Lstang

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Dec 6, 2003

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#1

• Feb 6, 2004

• #1

I've noticed that while cruising at 80 my oil pressure drops to between the A and L of the NORMAL gauge. I know these aren't the most accurate gauges, but is this normal? the dipstick showed plenty of oil, and driving in town the gauge shows right in the middle. What could cause this?

 

NKau

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#2

• Feb 6, 2004

• #2

As your engine warms up, so does the oil which in turn this out causing your oil pressure to drop. There's no real way to know what your true oil pressure is without some kind of aftermarket guage; the stock ones are notoriously poor. that being said, you should probably still see at least 25 psi cruising on the highway IMO. A good rule of thumb is 10 psi for every 1,000 rpm your engine is turning.

 

P

PRO50SC

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Dec 28, 2003

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#3

• Feb 6, 2004

• #3

Where did you get that rule of thumb figure from?
At idle, my o/p is at 25psi and anything above idle it's at 50 psi. That 10 per 1000 ain't workin' for me. I would definitly want to have more that 10 psi @ idle.

 

HISSIN50

"How long does it take to get help in here?

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#4

• Feb 6, 2004

• #4

Bernie, that is an old rule of thumb. its hard to be generic, as some motors like/need more pressure than others to function properly (i ve seen the rule referred to in regard to most small block american motors).
it seems that the rule applies to 302's as well. many have more pressure than that, but that is acceptable.

 

P

PRO50SC

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#5

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Thanks, I always say I learn somethin' new almost every day.

 

NKau

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#6

• Feb 6, 2004

• #6

Sorry, I should have been more specific. I don't know if there is any rule of thumb for warm idle, but I sure would want to see at least 20 psi at idle and then another 10 psi after 2,000 rpm (30 psi for 3,000......40 psi for 4.000 etc.)

 

HISSIN50

"How long does it take to get help in here?

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Feb 7, 2004

#7

• Feb 7, 2004

• #7

as i understand it, the rule is 10 psi/1K RPM in ANY condition (read worst condition). many may have more PSI, but this is the minumum you want to see no matter what. that is also about the time some pressure idiot lights are supposed to kick on (or 4 PSI for others i have had. Scary).

Big B, in regard to your last post: that's half the reason we are here. i have picked up tons of stuff i did not know before from this board (from you as well)

 

8

87gtconv

ragtopman

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#8

• Feb 7, 2004

• #8

I would say as an educated guess low oil pressure on the highway is OK cause as oil gets hot it looses some of its viscosity! If it pumps high when cold and lower when hot that is about all that the factory gauge can tell U and it would probably be OK! Also the more mileage you have on engine and pump more likely you are to see more of a diff between highway pressure and low speed pressure!

 

stangbear427

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Nov 11, 2002

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Feb 7, 2004

#9

• Feb 7, 2004

• #9

F8Lstang said:

I've noticed that while cruising at 80 my oil pressure drops to between the A and L of the NORMAL gauge. I know these aren't the most accurate gauges, but is this normal? the dipstick showed plenty of oil, and driving in town the gauge shows right in the middle. What could cause this?

Click to expand...

What transmission and gears do you have? Referring to the rule of thumb (10psi per 1K rpm) you probably only drive in what's considered to be "overdrive" on the highway. If you have the stock rear and T5, then 80mph will still have you around 2000rpm in 5th gear, which is bogging along. You can comfortably drive 75mph in 4th with the stock stuff, and you may see more pressure at those rpms. 5th gear as Ford gave it to us in our foxes is completely useless untill we change to lower rear gears. That being said, like NKau said- step one is to stop relying on the stock gauges- they are wrong and can't be trusted. I was amazed at the idiot show my stock oil pressure gauge was putting on when I added a mechanical AutoMeter to the dash- they do not tell the same story. I was panicking every other day, turns out over nothing.

 

Ranchero5.0

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Feb 7, 2004

#10

• Feb 7, 2004

• #10

If these guys would stop bickering for a minute...

You may have a plugged oil pickup and be starving the pump for oil or the oil drainbacks in the heads may be plugged with junk. With the motor warm, rev it to around 3k and see what the pressure does. It should go up a little and stay there. If it drops off you have a problem. A cheap gauge is only $20 and it's easy to install.

Jamie

 

stangbear427

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Feb 7, 2004

#11

• Feb 7, 2004

• #11

Jamie, are you in the right thread? I just re-read it three times, and I don't see any bickering. You're usually a pretty levelheaded guy in here, what are you talking about?