Weird oil pressure numbers

[Miraphone186]

Put in a new oil pressure sending unit today and it is reading higher at high RPMs, about 60 psi hot on the freeway at 60 mph, but at idle it drops below 10 to about 5 or something. I haven't checked for leaks yet as I had to go to work but could that be the case?

[kevinp661]

That can be the case.

It's pretty scary but your pressure could be dropping that low. I dealt with the same thing before replacing my engine (don't worry, wasn't related).

The common opinion seems to be that our stock FSJ gauges are more of an indicator that something does exist and work at least a little, but not indicate how well a component is working.

Zero oil pressure is a huge problem. 5-10 psi would be a problem at high RPM but it's probably "okay" at idle,... probably.

You could pick up a manual guage at the local PS, unscrew the factory sender and screw the mechanical into the same hole if you just wanted to verify the function or lack thereof of the stock gauge.

If you find it to be low and you want to increase it; the lowest cost option, I believe, is the oil pump rebuild kit, which is really just shims that go in your timing cover.

Good luck!

[kevinp661]

Oh...

And I wouldn't expect that a leak around the sending unit exists. Not one that would relieve low pressure but not high pressure anyway.

And why did you replace it? was it giving you the same readings this one did and you suspected they were bogus? Or was it just not functional at all?

[Miraphone186]

The new sender is reading differently, and yeah I replaced the old one because I thought it was bogus. The old sender would not go past 50 psi reguardless of how fast the engine is turning, but this one will read past 70 when cold. The old one read higher at idle but this one reads higher at speed. Another weird thing is that the gauge will.twitch when I use the power windows. I'll buy a mechanical gauge and check it later today.

[Miraphone186]

Just checked with a mechanical gauge, the sender wasn't that far off. The mechanical gauge reads 10 psi at hot idle. I guess at 153k miles a rebuild may be in order...

[Dumpy]

That's what I was thinking...rebuild time. Some pressure is better than no pressure, though

[Carnuck]

10 psi hot idle (depending on oil thickness) is pretty normal for AMC V8s

[Miraphone186]

I'm running 20w-50, if that means anything.

[Carnuck]

Pressure is a bit low. Could be the pump needs a new endplate or pressure spring?

[Thomas792]

I installed the mid plate without changing anything else when I replaced my timing case gaskets (oh the painful memories). Pressure went up about 20 psi cold and about 5 psi hot.

[joe]

10 psi hot idle (depending on oil thickness) is pretty normal for AMC V8s

Agreed not unusual for these motors. Not great pressure but adequate. I wouldn't go into the hand wringing rebuild mode yet. I would keep an eye on it and the temp gauge and an ear tuned for any top end noises. I would also make sure your cooling system is maintained with the proper mix and changed every two years. With low oil pressure the oil isn't removing heat from the bearings as fast as it normally would so you'll want your cooling system to keep the motor as cool as possible. Keeping it serviced and in tune to minimize heat build up goes a long way toward longevity. Depending how hard you drive it and miles/year you could easily get another few years out of it before needing a rebuild, or not. Good to be concerned and monitor it but not to fret. You do your part I'll bet the motor will do it's part.

[Miraphone186]

Pressure is a bit low. Could be the pump needs a new endplate or pressure spring?

Could it be the spring, it does seem like it wasn't a gradual change as it had good pressure only a few months ago. Also, I have a valve tick on cold starts that goesaway once the engine warms up, also starting fairly recently.

[Carnuck]

What brand filter? If it's orange, that could be 1/2 the problem (or THE problem)

[Miraphone186]

It's a purolator. Isn't there a spring in the timing cover as well?

[Carnuck]

yup