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Anonymous Poster
jkc191@sbcglobal.net
Sep 9, 2009, 3:45 PM
Post #1 of 7
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low oil pressure
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I recently bought a 1979 ford f250 with a 460 in it. The engine has 71000 original miles on it. I'm running 20-50 oil in it. When I first start the truck it holds about 60lbs. of oil pressure but after the engine gets to operating temp it idles at about 12psi. and at 2000rpm is at about 20psi. The truck has a bad rear main seal leak but I would think that as long as the oil level is full the oil pressure should still be normal. The truck doesn't smoke out the exhaust at all. I'm leaning towards needing to put a crank kit in it but wanted someone else's opinion before I attempt that feat.
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Hammer Time
Ultimate Carjunky
/ Moderator
Sep 9, 2009, 9:05 PM
Post #2 of 7
(3733 views)
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Re: low oil pressure
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We used to have a lot of problems with the Fords getting a lot of loose, crusty sludge that would be floating around the pan and plug up the pick up screen for the oil pump.
If not the case, then you likley need a new oil pump.
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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.
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DanD
Veteran
/ Moderator
Sep 9, 2009, 11:21 PM
Post #3 of 7
(3729 views)
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Re: low oil pressure
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You could always Plastigage the main & rod bearings and then know for sure that you just need an oil pump or whether you’re pulling the engine, too have the crank refinished and over sized bearings installed, along with a new pump.
I’m not going to go into a bunch of details on how to plastigage a crankshaft to determine the bearing to shaft clearances; you can Google it and get all kinds of how-to hits.
The short of it is; it’s a means of measuring the bearing clearances of the rod & main bearings. The plastigage itself is a thin plastic string that is placed on the crankshaft, with the bearing cap removed. The bearing cap is then reinstalled and torque to spec; you would then remove the cap again and measure the width of the squashed plastic string.
This measurement will represent the amount of clearance of that bearing. A rule of thumb is .0008” - .0015” clearance; myself I wouldn’t want to see anymore then about 10thou” max.
It’s kind of a long drawn out procedure and to tell you the truth, a real pain in the butt to do. Everything has to be super clean and oil free for the plastigage to work properly. If you don’t clean all of the oil away from the test area; it could cause the plastigage to become over squashed and give you a false reading.
You can no doubt imagine working underneath an exposed crankcase of an engine that has ran for whatever thousands of miles. The whole time trying to keep the oil off the bearing surface; let alone your eyes, hair, face whatever gets in the way of this oil dripping monster. LOL
Dam I’m almost sorry I’m suggesting to do this; but it’s the only way that you’ll know for sure, you’re not wasting your time and money.
Dan.
Canadian "EH"
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DanD
Veteran
/ Moderator
Sep 9, 2009, 11:48 PM
Post #5 of 7
(3720 views)
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Re: low oil pressure
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I hate playing the odds, when it comes too spending time, energy and MONEY!
But hey it’s not my crap shoot; throw the dice and take your chances.
Dan.
Canadian "EH"
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Tom Greenleaf
Ultimate Carjunky
/ Moderator
Sep 10, 2009, 1:34 AM
Post #6 of 7
(3708 views)
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Re: low oil pressure
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Late comment + opinion/guess:
A Ford 460 is good for 250k IMO but with a rear main leaking it probably ran way too low on oil and wrecked the main bearings. If high vis oil can only do 12 psi there's trouble! Red light should be on as a further warning. If sludged out as said already the oil pick up could be plugging or return holes from valve covers/heads blocked such that engine thinks and is low on oil in the pan,
T
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Loren Champlain Sr
Veteran
/ Moderator
Sep 10, 2009, 10:57 AM
Post #7 of 7
(3698 views)
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Re: low oil pressure
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Okay; My two cents worth; Are you testing the oil pressure with an actual guage or by the dash guage? Remove the oil pressure sending unit and connect an oil pressure guage. Allow the engine to warm, then take your readings. I can get specs, if you wish. I'd agree with HT. I've also seen the pickup tubes fall off of the oil pump.
Loren
SW Washington
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