Oil pressure comes and goes, 96 e350 motorhome

Hey guys. Got a strange one. 96 460 Ford in a E-Superduty chassis. On start-up, the oil pressure reads zero. The lifters clack, loud. After 10-60 seconds, the gauge pops up off zero to about middle. Lifter tick slowly goes away. While driving, lifter noise is minimal, but gets worse when hot, or loaded for long periods, like pulling a long hill. I've tried thicker oil, and its currently running 15-40 Rotella with half a qt of Lucas oil stabilizer. This change helped the ticking when hot, but made the cold start no pressure issue worse. It takes longer to get pressure when cold, and even when it does come up, it will sometimes go back to zero again. This could be gauge related, but the lifter noise does coincide with oil pressure readings. An old Ford mech I know said that the oil pumps in these have a spring in the releif that fails. Is this a likely cause? I can only go about 500 miles on fresh oil before the lifter noise and low oil pressure at start up become an issue. The motor only has 60k. It does not burn oil, nor leak. I am planning to put in a better oil pressure gauge, im reasonably certain that will confirm the above.

Thoughts?

The first step is to put a real gauge on there.  My recollection is that while those have a gauge it really only shows that there is pressure and that the position of the needle on the dial is meaningless.  Actually, the first step is to stop driving it.  You're clearly running it with low oil pressure and if the issue is a stuck relief valve you're causing considerable additional damage by running it.

If it's clacking that bad, I don't think a real oil gauge is needed.  Your ears are supporting the gauge's diagnosis.

Bad pump, crap on the pickup screen, busted bypass spring, wasted oil pump, air sucking in around the pickup tube where it meets the pump... Pan needs to come off.  If you've been driving it long enough to get it hot with oil pressure that low, you should probably also pull a few main and rod bearings to check.  460s do not have priority main oiling.  They lube the cam first, and the rods and mains get oil after that, so if the oil pressure is low enough to collapse the lifters, imagine how low the oil pressure is at the crankshaft.

Not trying to sound apocalyptic, but stop running the engine now.  Seriously.  I would even be concerned about starting it to pull it in the barn to do the work.  Push it or drag it with something else.

APEowner said:

The first step is to put a real gauge on there.  My recollection is that while those have a gauge it really only shows that there is pressure and that the position of the needle on the dial is meaningless.  Actually, the first step is to stop driving it.  You're clearly running it with low oil pressure and if the issue is a stuck relief valve you're causing considerable additional damage by running it.

You are correct.  If I remember correctly the sender is actually a switch that shows pressure at 6PSI.  Fairly easy fix for that, though.  I can't find the one that's relevant for an F series or E series, but here are a couple for fox bodies and rangers.  Same procedure

Recommended for any owner of a Ford from '87 through the mid-late 90s.

https://www.tccoa.com/threads/how-to-convert-your-oil-pressure-gauge-with-pics.75977/

https://www.therangerstation.com/forums/index.php?threads/variable-oil-pressure-gauge-modifiction.165083/

As others have said; you need to have someone drop the oil pan and take a look inside. At the very least I'd replace the oil pressure sending unit and the oil pump.  I'd also look at the rod bearings. If they are OK then the mains most likely are OK too.  The condition od the pan and bottom end will also tell you if the oil system is crudded up which may  be a contributing factor to your oil pressure issueses.

I had a Chevy Sub. with the 454 that had low oil pressure, 17-20 at cruze speed and near 5 psi at idle.  I dropped the pan, inspected the rod bearings and ended up replacing them all.  The mains were fine. I also installed a high volume oil pump at the same time.  At start up I then got 60-70 psi and never less than 35 psi.  

Curtis is correct that you probably don't need to measure the actual pressure.  There's clearly an internal problem.  I still would because it gives you part of the picture of what's going on and also because I'm an engineer and if there's data to be gotten I want to get it but that may speak to a larger issue with me rather than what's going on with your engine.

APEowner said:

Curtis is correct that you probably don't need to measure the actual pressure.  There's clearly an internal problem.  I still would because it gives you part of the picture of what's going on and also because I'm an engineer and if there's data to be gotten I want to get it but that may speak to a larger issue with me rather than what's going on with your engine.

It can never hurt to measure actual pressure, though, as you mentioned.  Ford's dummy gauges don't tell you much.

If thicker oil makes the cold start/idle pressure worse, that points to a leak upstream of the oil pump.  Bad gasket/O-ring or cracked tube.

A quick and dirty way to check is to jack the back end up as high as you possibly can, like 2-3 feet off the ground, and start it and see if it's improved.

Thanks guys. I appreciate the input. Sadly, it will need driven about 3 more miles to my barn, but I drove it over 4000mi with this issue, so what's three more?

Off goes the pan... stay tuned.

Oil pump.  Unfortunately you probably already have damage that will rear its head later.  So yes, check the rod bearings. 

I do remember the days of yesteryear when thicker oil, maybe with STP added, was a stop gap for advancing engine wear, so understand the approach.

To me it sounds like a cracked or otherwise air-leaking pickup tube. 

In reply to jmthunderbirdturbo :

Let it warm up as much as possible!