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Uh Oh! Low oil pressure
#1
Well, crud!

I got my electronic Autometer gauge in my '73 (351C, 2V) last night, and when I started the car up, it registered about 65 psi. After it was thoroughly warmed up, I was getting about 15 psi at idle in park Sad. It was lower when the car was in gear. When I stand on the gas and rev it up to over 3K rpms, it gets over 30 PSI and approaches 40, and it doesn't spike, but it goes up slowly. Traveling at about 60 mph, it registers a solid 25 or so psi.

Should I be looking to get a new engine or rebuild? This sounds like very low readings to me. I really don't hear any bad sounds from the motor that sound like rods knocking or main bearings....but I'm still worried.

Thanks,

Joe

1973 Mustang Hardtop 351C 2V
2010 Harley-Davidson Street Bob
2002 Excursion 7.3L Diesel
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#2
A general rule of thumb is 10 psi for every 1000 rpm, so it sounds like you're in the ball park. Electronic gauges are dampered so that the readings don't jump around, which may be why you're seeing the gradual climb.

A mechanical gauge will usually give you better information, and can also indicate when your main bearings are worn. If, when you are accelerating, maintaining speed, or decelerating and the pressure changes at the same speed/rpm you likely have some bearing issues. Usually, electronic gauges are too dampered to show much, if any immediate change.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
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#3
jmcgill89;56647 Wrote:Well, crud!

I got my electronic Autometer gauge in my '73 (351C, 2V) last night, and when I started the car up, it registered about 65 psi. After it was thoroughly warmed up, I was getting about 15 psi at idle in park Sad. It was lower when the car was in gear. When I stand on the gas and rev it up to over 3K rpms, it gets over 30 PSI and approaches 40, and it doesn't spike, but it goes up slowly. Traveling at about 60 mph, it registers a solid 25 or so psi.

Should I be looking to get a new engine or rebuild? This sounds like very low readings to me. I really don't hear any bad sounds from the motor that sound like rods knocking or main bearings....but I'm still worried.

Thanks,

Joe

Pretty common in a old Ford imo
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#4
I'm going to monitor it closely, and maybe switch to 20w50 or 30 weight oil. It's got 10w40 in there now.

Is it tough to change the oil pump on these motors?

1973 Mustang Hardtop 351C 2V
2010 Harley-Davidson Street Bob
2002 Excursion 7.3L Diesel
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#5
My 5.0 has registered zero (on the stock gauge) at idle since I bought it 25K miles ago. tried different oil viscosities, makes little to no difference when hot. Has no knocks or ticks, pressure rises with RPM.
No worries.

Pete - MotoArts Decals and Signs
'71 Sportsroof 351C-4V/4-speed - FINALLY under construction - no, wait, on hold again...
'90 Mustang 7-Up 5.0 ragtop, rolling beater
'66 Sunbeam Tiger Mk.IA, survivor
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#6
IMO, it's nothing to worry about or do something about (like changing oil pump or viscosities). If the performance is satisfactory, leave it alone. However, if the oil pressure decreases significantly or disappears, you'll know it's time to take action. For now, though, I don't see a big problem.

Doc

PS Changing the oil pump is a real PITA, requiring hoisting up the motor to remove the oil pan, etc.

Doc

[Image: 6y14ea.jpg]

Project started 8-7-10
Completed: All new suspension, rebuilt 351C H Code bored .030 over with mild cam and intake, new 3.50 TracLok, custom exhaust system
Current "mini-project": interior upgrade Undecided
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#7
It sounds like it has a lot of miles on it or it was run too low on oil once too often and the clearances of the bearings and or the oil pump has opened up a bit. The Ford manual calls out oil pressure at operating temperature and at 2000 RPM to between 50 and 70 PSI. If you are driving it "normally" it will probably be fine as long you don't hear any knocking when revved or all the lifters rattling at idle. Changing the pan is a bit of a pain but can be done. Unless you just want to take the engine apart, I'd drive it and watch for any changes in oil pressure and or ugly noises. Chuck

PS the only complete failure of an oil pump I've experienced on a car I owned was a 1990 5.0 mustang. The OEM pump housing is aluminum and the rotors are steel. Don't ask me why. At idle he rotor seized to the housing and twisted the oil pump drive shaft in half. A quick shutdown and a rollback wrecker prevented any further damage.
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#8
Lifter noise would be tapping on the top side of the motor, right? If I remember correctly, a rod knock would make itself heard after a decrease in RPMs after sustained high speed running.

The only sound I hear that could be taken as a tapping is coming from underneath the car. I had been figuring it to be a small exhaust leak.

I guess the motor does not actually have 60,000 miles on it if it's got this kind of low oil pressure.

1973 Mustang Hardtop 351C 2V
2010 Harley-Davidson Street Bob
2002 Excursion 7.3L Diesel
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#9
Did you install a new sender with the gauge. I've seen senders go bad and give false readings. With that being said, as long as you're not hearing lifter or rod noise, as mentioned earlier, and you're not pushing the engine real hard, you should be ok for now.

Steve
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#10
jmcgill89;56704 Wrote:Lifter noise would be tapping on the top side of the motor, right? If I remember correctly, a rod knock would make itself heard after a decrease in RPMs after sustained high speed running.

The only sound I hear that could be taken as a tapping is coming from underneath the car. I had been figuring it to be a small exhaust leak.

I guess the motor does not actually have 60,000 miles on it if it's got this kind of low oil pressure.

The lifter noise would be several rapidly occurring, near simultaneous pronounced clicking sounds. A rod knock is usually less rapidly occurring, deeper in the engine, and sounds more like an actual knock. Simulating sounds with words is difficult, sorry if I'm not clear. It may have 60K miles on it. A lot of things affect engine life, how hard it's used, how it is maintained, fuel contamination due to rich or flooding carb, etc. In the old days engines didn't last as long as they do now. Advances in fuels, fuel injection, electronic ignition, and engine design all contribute to a modern engine lasting a lot longer.
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