Oil pressure loss
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Oil pressure loss
I have a 76 F150 with a 390 and a 4 speed. The truck runs good and has good power, but the oil pressure guage shows no pressure at an idle when the engine is warm. However, while traveling at 55mph at about 2200 rpm; it shows good pressure. I don't know whether to suspect my guage, sending unit, or oil pump. it really just doesn't make sense to me. Any thoughts or help would be appreciated. Thanks.
Fleet Mechanic
Joined: Jul 1999
Posts: 1,360
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From: Iowa
That sounds pretty typical of most broke-in FE's... What type of oil pressure guage are you running?
For a while, my old Ford would hold 30-35psi on the highway, but the needle would rest on the peg when I let it idle. When it would only hold 22psi @ 2,500rpm, I put new bearings in the bottom end, along with a new oil pump and shaft.
For a while, my old Ford would hold 30-35psi on the highway, but the needle would rest on the peg when I let it idle. When it would only hold 22psi @ 2,500rpm, I put new bearings in the bottom end, along with a new oil pump and shaft.
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I am just running the stock guage in the dash. The motor has been rebuilt within the last 50,000 miles with new bearings, rings, oil pump, etc. I am not sure what kind of pressure i am running on the highway, but I know the needle goes to the high side of the middle of the gauge. The hotter the engine gets, the less pressure I have.
Fleet Mechanic
Joined: Jul 1999
Posts: 1,360
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From: Iowa
Ford guages and senders are notorious for causing anxiety and in some cases, panic.
More than likely, there's nothing wrong with your system. If you're in doubt, you could either hook up a mechanical guage temporarily, or install one permanantly. You could use a 1/8" close nipple and a "T" pipe fitting to create a place to add the mechanical guage and still use the in-dash guage.
More than likely, there's nothing wrong with your system. If you're in doubt, you could either hook up a mechanical guage temporarily, or install one permanantly. You could use a 1/8" close nipple and a "T" pipe fitting to create a place to add the mechanical guage and still use the in-dash guage.
Last edited by 390fe; Jul 7, 2007 at 01:21 PM. Reason: Add more info
Postmaster
Joined: Jul 2003
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From: Pittsburgh
Ehh, for the cost of a sending unit you can just buy and install a mechanical gauge. They're both about $15.
I was having the issue that when my motor was hot idling the gauge would sit on the peg, but cruising down the interstate it'd make 50-60 PSI no problem. When i pulled the motor out to replace the flywheel i found that the oil gallery plugs in the back of the block were leaking. Not terribly, but you could see where it was.
i replaced those and since it'll read about 12 or 15 at a hot idle.
Not saying this is your problem, but sometimes the issues can be hidden.
Justin
I was having the issue that when my motor was hot idling the gauge would sit on the peg, but cruising down the interstate it'd make 50-60 PSI no problem. When i pulled the motor out to replace the flywheel i found that the oil gallery plugs in the back of the block were leaking. Not terribly, but you could see where it was.
i replaced those and since it'll read about 12 or 15 at a hot idle.
Not saying this is your problem, but sometimes the issues can be hidden.
Justin
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From: NE Ga
Put a mechanical gauge on it w/ copper tubing, not the white plastic they give you w/ the gauge. When that stuff blows in the engine comp from heat...well you know the rest.
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Postmaster
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By any chance are any of your other guages reading low? The oil pressure, temp and gas guages all operate off the same voltage source. The part is called the ICVR (Instrument cluster voltage regulator). It is not uncommon for these regulators to fail and cause low readings. The regulator is mounted on the back of the instrument cluster.
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Hey, I just wanted to let everyone know that I changed my oil pressure sending unit last night, and the pressure is back to normal. When the the truck is hot and idling, the guage comes to rest well within the normal range. Thank you all for your support and ideas.
Posting Guru
Joined: Aug 2005
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From: NE Ga
Well wouldn't ya know it. I go to drive my truck tonight and my SunPro mehcanical oil gauge is dancing all over the marks. Not sure if the gauge went bad or if the line got plugged. I thought sunpro was decent stuff even though they are rather cheap. Good thing it's got a one year warranty though. I think this time I'm gonna T it to where i can run my stock gauge too.
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