5.8L 351 low oil pressure - Ford Truck Enthusiasts Forums

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5.8L 351 low oil pressure

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Old 04-16-2018, 07:07 PM
kyle m
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5.8L 351 low oil pressure

I got this old beater for yard projects. It read between L and middle when I first got, it and I know about the idiot light gauge so I figured it was that. Finally get around to my first oil change and since then it's at L all the time. The sender is of course old but it wasn't this low before. Could it be different oil? I put in 5w-30 as it's i the Haynes manual.

I wanted to put in a mechanical gauge to avoid all this but forgot what sender unit I'd need to make it work with the dash.
 
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Old 04-16-2018, 08:46 PM
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Never heard of 5W for these trucks. I was always informed 10W-30 and that's what I've always used. It could be the oil pump going bad. That's the first guess as it matches the symptoms when my pump gave.
 
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Old 04-16-2018, 09:42 PM
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5W-30 is spec'd for the 5.8L in my Ford owner's manual.

I'd put a mechanical gauge on it before doing anything else. I have a T-fitting off of a 4" extension pipe on the block, one port of the T is used for the factory sender and the other is used to feed the mechanical gauge. My mechanical is just under the hood, for diagnostic/monitoring purposes.
 
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Old 04-17-2018, 12:18 AM
kyle m
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Do you remember the fitting thread size? AND also you put in the oem sending unit and not a previous model unit? I ask because I've seen people use previous models too
 
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Old 04-17-2018, 01:37 AM
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It's 3/8ths NPT. You need a 4 inch nipple.

Possibly a reducer down to a 1/4 NPT (national pipe thread)

This is mine with a T and original sender + sender for Autometer electric.

You could use a mechanical just as easy

 
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Old 04-17-2018, 04:33 AM
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Oil weight is just a suggestion unless like the newer cars that will have it on the fill cap like 0w20, but they always have a chart and depending on your climate you may need to adjust. Worn bearings use 20w50 ect it will pump regardless of the grade.
 
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Old 04-17-2018, 02:37 PM
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Originally Posted by Scndsin View Post
It's 3/8ths NPT. You need a 4 inch nipple.

Possibly a reducer down to a 1/4 NPT (national pipe thread)

This is mine with a T and original sender + sender for Autometer electric.

You could use a mechanical just as easy

that's exactly what I needed. Thanks. That's also the cleanest engine I've ever seen
 
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Old 04-17-2018, 02:38 PM
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Did you torque it down to a specific amount or just until it was snug and the tee was vertical?
 
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Old 04-17-2018, 02:52 PM
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only insane people would go by the stock gauge, no diagnosis should be started without a mechanical gauge
 
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Old 04-17-2018, 02:54 PM
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Originally Posted by kyle m View Post
Did you torque it down to a specific amount or just until it was snug and the tee was vertical?
Standard shade-tree mechanic unit of measurement: 1/4 turned past the snapping point
 
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Old 04-17-2018, 04:20 PM
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Originally Posted by kyle m View Post
I got this old beater for yard projects. It read between L and middle when I first got, it and I know about the idiot light gauge so I figured it was that. Finally get around to my first oil change and since then it's at L all the time. The sender is of course old but it wasn't this low before. Could it be different oil? I put in 5w-30 as it's i the Haynes manual.

I wanted to put in a mechanical gauge to avoid all this but forgot what sender unit I'd need to make it work with the dash.
My advise..there is more guarantee to watch a mechanical gauge to tell you the truth And my 1990 which i bought new f-250 351W after the break in oil was drained she never saw anything but 20-50 Mobil one synthetic..It paid off she still runin strong great compression in every cyl.
I may be tempted to run that 5w sewing machine oil in her if i was back in the Arctic winter
I put a mechanical gauge in her within a year of buying it with light...just a little one...still works well today..there way more variables for error with the sending unit
 
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Old 04-17-2018, 04:25 PM
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Originally Posted by kyle m View Post
Did you torque it down to a specific amount or just until it was snug and the tee was vertical?
NPT is a tapered cut, so you can bring it to "where you need it" & it still seals.

I don't ever screw pipe down till it stops dead.

But Randy knows more than I do bout' mechanicin'...
 
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Old 04-17-2018, 04:34 PM
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Originally Posted by Scndsin View Post
But Randy knows more than I do bout' mechanicin'...
LOL David!
 
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