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Oil Pressure gauge ...


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... moves between a little below middle line to 3/4 line while running, but when turn off and turn on again, does go to 0 like normal. Just started doing this. Sending unit?

Just started doing what? The behavior you are describing sounds normal to me. If it's normal now and you're worried about it, what did it do before and why WEREN'T you concerned about it?

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Start it and op jumps to 60 psi at idle. Drive and goes to about 70. When warm drops to about 40 at idle and shows 60-65 at hwy speed. Used to show when cold about 40 at idle and 60 when going, then 20 or so at idle when warm and about 50 with rpms up. When I shut it off, needle has always stayed showing the op it had when shut off but when I turn ign switch on again needle goes to zero before starting. It's always done that (normal, I understand), and still does that. Anyway, it's as though the whole scale shifted up about 20 psi.

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Start it and op jumps to 60 psi at idle. Drive and goes to about 70. When warm drops to about 40 at idle and shows 60-65 at hwy speed. Used to show when cold about 40 at idle and 60 when going, then 20 or so at idle when warm and about 50 with rpms up. When I shut it off, needle has always stayed showing the op it had when shut off but when I turn ign switch on again needle goes to zero before starting. It's always done that (normal, I understand), and still does that. Anyway, it's as though the whole scale shifted up about 20 psi.

Okay, then eliminate variables. First, aside from the range of movement shifting higher on the scale, everything acts properly. Cold oil is thicker so the pressure is higher right after a cold start, then drops off as the engine warms up. Oil pressure is lower at low RPM and goes up as the RPMs increase. (Some people claim it "should" go up 10 psi for every 1000 RPM - in well over a million miles of driving many vehicles, I have NEVER seen any vehicle do this.)

 

So ... what might be different to have caused the change? Have you recently done an oil change (or had the oil changed)? Is the oil the same brand you always use? Is the oil the same weight/viscosity you always use? Did you go from conventional oil to synthetic, or the opposite? Is the filter the same brand and model, or did you use a different filter than what you normally use?

 

Any of the above could, potentially, affect oil pressure readings.

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Same oil

 

Same filter

 

 

getting close to needing a change.

 

 

I need to do a manual read on it to make sure I don't have a relief valve issue or something like that. I think I will do an oil change also and see what happens. I suppose I should take everyone's advice :smart: and switch from fram also. :brows:

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FRAM!?!?!?

 

OHMIGAWD!

 

There's your problem, right there. Go buy a Mobil-1 or Purolator filter ASAP.

 

FYI, the factory spec (with a warm engine) is 13 psi minimum at idle, 37 to 75 psi above 1600 RPM. I think the relief valve is set for 75 psi, so unless you are exceeding 75 psi you do not have a relief valve problem.

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Why did I not know you would say that about Fram!!! :yes:

 

No, goes not about 75, so that's good news.

 

Thanks, Eagle!

 

BTW, IF it is a filter problem, this is the FIRST one in at least 30 years of using only Frams on ALL my cars! :nanner: But, to get everyone to be nice to me :brows: I will switch filters!!!! :thumbsup:

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The OEM sender on my '90 4.0 is a two piece sending unit. There's the sensor itself, with a plastic cap that has a small spring contact that rest on a metal cap of the sensor. This plastic caps snaps on/off and has an o-ring to seal out dirt and moisture. The wire has a rubber boot that fits over the terminal on the cap. The o-ring doesn't always do its job well. In really wet weather conditions, it builds condensation, or somehow gets a slight amount of moisture under the cap, and causes the oil pressure to read higher than normal. Also causes some fluctuating pressure readings under steady state RPMs, with the needle jumping up and down between the correct pressure and 20-30 psi higher. The reason for this is that the moisture buildup causes some resistance between the contacts inside the cap. Snap the cap off and thoroughly dry the inside of the cap and wipe off the sensor, and see if that helps. It's cured my fluctuating gauge whenever it's occurred (there have been times when the gauge pegged on the high side).

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