What are causes of low oil pressure? I know the level is fine as I just changed the oil a few weeks ago.
oil light?
Postmaster
Joined: Jul 2003
Posts: 2,544
Likes: 2
From: okc
the first thing you need to do is purchase a oil pressure guage and find out what the pressure really is, its hard to tell with those lights if you have low pressure or if the sending unit is bad, i would suggest buying a triple guage setup, finding a nice place to mount it and never looking back at the old style lights and guages, when u find out what kind of oil pressure you have let us know and we might come up with some theories of what your problem might be................
Posting Guru
Joined: Feb 2002
Posts: 2,404
Likes: 3
From: Cleveland, WI USA
If it's truely low oil pressure, it could be a blown head gasket which would also result in smoke from the exhaust. It could also be a bad oil pump or bad bearings.
Someone correct me if I'm wrong, but I believe oil flows to the main bearings first, then the rod bearings and then the cam bearings. The cam bearings might get oil at the same time as the mains though - can't remember. If the bearings are worn, oil leaks out between them and the journals and the pressure to the sensor is reduced.
On my 460, I replaced my pump, mains and rod bearings and still lose pressure when it's hot. I'm 99% sure it's my cam bearings.
As stated above, get a tripple guage set w/oil pressure. The one I got must be for higher pressure pumps/engines as it goes from 8psi to some ungodly high number. I'd get one that goes from 1-50 or so.
Just my $0.02.
Kevin K.
Someone correct me if I'm wrong, but I believe oil flows to the main bearings first, then the rod bearings and then the cam bearings. The cam bearings might get oil at the same time as the mains though - can't remember. If the bearings are worn, oil leaks out between them and the journals and the pressure to the sensor is reduced.
On my 460, I replaced my pump, mains and rod bearings and still lose pressure when it's hot. I'm 99% sure it's my cam bearings.
As stated above, get a tripple guage set w/oil pressure. The one I got must be for higher pressure pumps/engines as it goes from 8psi to some ungodly high number. I'd get one that goes from 1-50 or so.
Just my $0.02.
Kevin K.
Thread Starter
|
Senior User
Joined: Aug 2004
Posts: 382
Likes: 0
thanks
I don't think it's the head gasket because the oil looked fine last week and it does not smoke other than a few seconds on startup when it's cold.
I just replaced the oil pan a few months ago and never thought to check the bearings or anything while I was in there.
I don't think it's the head gasket because the oil looked fine last week and it does not smoke other than a few seconds on startup when it's cold.
I just replaced the oil pan a few months ago and never thought to check the bearings or anything while I was in there.
New User
Joined: Jan 2008
Posts: 0
Likes: 24
The 351M/400 were notorious for oiling problems.
What causes low oil pressure ?
1) Wear on engine parts (usually the culprit)
2) Plugging filter
3) Piece of foreign material in oiling system (partially plugged Sending unit)
4) Faulty Sending Unit
This topic is considered a general engine topic.
It isn't 73-79 specific.
What causes low oil pressure ?
1) Wear on engine parts (usually the culprit)
2) Plugging filter
3) Piece of foreign material in oiling system (partially plugged Sending unit)
4) Faulty Sending Unit
This topic is considered a general engine topic.
It isn't 73-79 specific.
Trending Topics
Posting Guru
Joined: Feb 2002
Posts: 2,404
Likes: 3
From: Cleveland, WI USA
Originally Posted by Mil1ion
This topic is considered a general engine topic.
It isn't 73-79 specific.
It isn't 73-79 specific.
K.
FTE Stories
Ford Trucks for Ford Truck Enthusiasts
10 Best Ford Truck Engines We Miss the Most!
Joe Kucinski
2026 Shelby F-150 Off-Road: Better Than a Raptor R?
Brett Foote
2027 Super Duty Carhartt Package First Look: 12 Things You NEED to Know!
Michael S. Palmer
10 Most Surprising 2026 Ford Truck Features!
Joe Kucinski
Top 10 Ford Trucks Coming to Mecum Indy 2026
Brett Foote
5 Best / 5 Worst Ford Truck Wheels of All Time
Joe Kucinski
Ford Super Duty: 5 Things Owners LOVE, 5 Things They LOATHE!
Joe Kucinski
Every 2026 Ford Truck Engine RANKED from WORST to FIRST!
Michael S. Palmer
The Best F-150 Deal of Every Trim Level (XL through Raptor)
Joe Kucinski
New User
Joined: Jan 2008
Posts: 0
Likes: 24
Actually Oil Light's flash/flicker on other years trucks as well.
It's Either Electrical or Oiling system or both problem.
The year of truck has nothing to do with it.
This is the mis-conception about the year specific questions.
Just because the vehicle involved is a 73-79 doesn't make it a 73-79 specific problem.
Maybe read the read first threads at the top.
It's Either Electrical or Oiling system or both problem.
The year of truck has nothing to do with it.
This is the mis-conception about the year specific questions.
Just because the vehicle involved is a 73-79 doesn't make it a 73-79 specific problem.
Maybe read the read first threads at the top.
Posting Guru
Joined: Nov 2003
Posts: 1,230
Likes: 0
From: East Flat Rock NC
A few years ago I installed a HV oil pump in a 79 F-100 2x4 351w someone
before I bought it installed felpro valve cover gaskets these gaskets had the
small rings were the bolts go in, well they let one of these small rings fall in the engine and it made its way to the oil pump and locked it down! The F-100
had the gage set mounted under the dash and after I primed the engine and
cranked it,it had 80-90 psi oil presure and the oil light came on (Bright) and
stayed on!
Maybe in some cases high oil pressure can cause this!
before I bought it installed felpro valve cover gaskets these gaskets had the
small rings were the bolts go in, well they let one of these small rings fall in the engine and it made its way to the oil pump and locked it down! The F-100
had the gage set mounted under the dash and after I primed the engine and
cranked it,it had 80-90 psi oil presure and the oil light came on (Bright) and
stayed on!
Maybe in some cases high oil pressure can cause this!
Postmaster
Joined: Jul 2003
Posts: 2,544
Likes: 2
From: okc
i bet having too much oil pressure would trigger the sending unit, if your pressure is too high you risk blowing out seals, thats why its important to hone out certain oil ports to improve flow and keep oil pressure in tolerable ranges when you put in HV pumps.....80 psi is safe but much more than that isnt neccesary....im looking into buying an external oil pump someday, not just a preluber either, a full time electric pump on a keyed switch...
Cross-Country
Joined: May 2003
Posts: 78
Likes: 4
From: Middle of America
I have noticed that a 351M/400 doesn't carry a bunch of oil pressure and after they get tired it does drop at idle in gear to a rather low pressure. Minimum of 10lbs per 1000 of rpms desired is what my machine shops says so 10lbs at idle is supposed to be eneogh but the only engines I have ever had that carried that low of pressure were shot. The standard motor parts oil pressure sending units used to turn on at 7lbs, or at least thats what the rep claimed that supplied our autoparts store. My guess is the motor is getting tired in bearing department.