5 PSI at idle!!??
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Senior User
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5 PSI at idle!!??
I just put in a Melling high volume oil pump in my 79 F-150, 351M. I'm running 20W50 oil and once it gets hot, I'm only getting 5 psi at idle with the truck in gear- what gives? At startup it's at 60 and then goes down from there. Running down the road when it's hot it's around 25. Is 5 psi too low to drive it? What would cause such low pressure?? Any help would be greatly appreciated.
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5 PSI at idle!!??
No hot oil pressure is an indication of worn crankshaft bearings. How many miles on the truck? You are probably looking at replacing the crank bearings. Cam bearings can in rare instances cause this but I'd say crank bearings. 5 lbs is a little too low especially with new oil.
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From: Virginia
5 PSI at idle!!??
Too much clearance in the main and rod bearings. I don't
know if you should worry about it or not. It's personal
preference I guess. I've run engines pretty loose for awhile,
but I knew it and planned accordingly, saving money up
for the upcoming rebuild. I even had one I ran, that in the
summer setting at a stoplight you could here the mains making
a very heavy thump thump sound.
know if you should worry about it or not. It's personal
preference I guess. I've run engines pretty loose for awhile,
but I knew it and planned accordingly, saving money up
for the upcoming rebuild. I even had one I ran, that in the
summer setting at a stoplight you could here the mains making
a very heavy thump thump sound.
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From: Nebraska Farm
5 PSI at idle!!??
I've had the same problem with mine since it was rebuilt. I didn't grind the crank and oversize the bearings, but after reading these posts, maybe I should have. Mine drops to 5-10 psi at a stoplight also. I'm not going to worry about it, maybe I should just take the gauges out.
Dave,
79 F-150 4x4, 390 w/C6, Edelbrock carb, 33X12.50 never will be finished.
Dave,
79 F-150 4x4, 390 w/C6, Edelbrock carb, 33X12.50 never will be finished.
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5 PSI at idle!!??
i old motor i had in my f150 was 351M and it had low oil pressure, but i didn't know it till the gauage went out and i had to stick a mechanical on it. it ran 5psi at idle. i talked to a friend who used to be a factory trained ford mechanic. HE said that 5psi for about every one thousand rpm was good. i still replaced the motor reasons other than the oil pressure. guess it's all in what you consider safe. or comfortable running.
lr
lr
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5 PSI at idle!!??
thanks. I bought the truck last July in Fort Walton Beach, FL (while at Hurlburt Field AF Base) and drove it up to Spartanburg, SC. The odometer says 34,000, who knows how many miles it actually has. I know the motor's not original, by the fact that it had a 2wd oil pan on it and was hitting the front axle (finally found a 4wd pan at AutoKrafters). Guess I'll push the 351M till it gives out. It's a strong running truck, but it is running fairly loose. Anybody had any experience with Auto Zone or Advanced Auto engines?
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Senior User
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5 PSI at idle!!??
Well, Melling markets the pump as a "high volume" pump. Increased volume will increase the pressure because you have increased flow in the same constricted space (the engine), but I know what you meant. haha.
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5 PSI at idle!!??
Small world, I'm stationed at Eglin AFB. My 390 doesn't have #'d gauges just the stock bad or good but at idle at a lite when hot I am below the low mark don't have a clue what psi it is but been running that way for about two yrs. back and forth from Crestview to base 50 miles round trip not a problem yet. knock on wood!
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5 PSI at idle!!??
I would not buy another engine from Autozone. Just my experience. Get some references for a local rebuilder and check for customer satisfaction and price.
1977 F-100
300 I-6 / C-4
Offy intake w/holley390
Hedman headers w/duals
MSD6
Whiter whites/Brighter brights
1977 F-100
300 I-6 / C-4
Offy intake w/holley390
Hedman headers w/duals
MSD6
Whiter whites/Brighter brights
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From: PacNW
5 PSI at idle!!??
>I just put in a Melling
>high volume oil pump in
>my 79 F-150, 351M.
>I'm running 20W50 oil and
>once it gets hot, I'm
>only getting 5 psi at
>idle with the truck in
>gear- what gives? At
>startup it's at 60 and
>then goes down from there.
> Running down the road
>when it's hot it's around
>25. Is 5 psi
>too low to drive it?
> What would cause such
>low pressure?? Any help
>would be greatly appreciated.
5 psi is low but at idle it's probably not too low. It does indicate that you have a worn engine specifically the main and rod bearings. The rule of thumb is 10 psi for every 1000 rpm so 25 isn't too bad but you're going to need an overhaul soon. When you do then add the line from the oil passage in front of the fuel pump to the O.P. sending unit port. This'll give you better flow to the places you need it.
>high volume oil pump in
>my 79 F-150, 351M.
>I'm running 20W50 oil and
>once it gets hot, I'm
>only getting 5 psi at
>idle with the truck in
>gear- what gives? At
>startup it's at 60 and
>then goes down from there.
> Running down the road
>when it's hot it's around
>25. Is 5 psi
>too low to drive it?
> What would cause such
>low pressure?? Any help
>would be greatly appreciated.
5 psi is low but at idle it's probably not too low. It does indicate that you have a worn engine specifically the main and rod bearings. The rule of thumb is 10 psi for every 1000 rpm so 25 isn't too bad but you're going to need an overhaul soon. When you do then add the line from the oil passage in front of the fuel pump to the O.P. sending unit port. This'll give you better flow to the places you need it.