I recently bought a second vehicle, a beater truck off Craigslist to wrench on with the girlfriend. I ended up with a 1996 Ford F-150 XL, under the hood sits a 5.0L Windsor mated to an automatic (AODE?) transmission. Rear wheel drive with 185,000 miles on the clock.

Installed a new NAPA fuel filter, eight new spark plugs, new gasket and fluid in the rear differential, Motorcraft FL-1A oil filter and 6 quarts of Motorcraft 10W-30 synthetic motor oil.

Drove it for about a month with no major issues to report. Up until recently the oil pressure gauge started bouncing around while idling at red lights. I read online the factory oil pressure gauges are not very accurate so I removed the oil pressure switch on the engine block and installed a mechanical oil pressure gauge.

Start up: 20 PSI
Slowly starts to drop as the engine warms up while idling in my driveway. Oil pressure will eventually drop to 0 PSI. Cruising on the interstate at 70 MPH the oil pressure will be a steady 30 PSI. It will drop right back to 0 PSI once stopped at the first red light off the interstate combined with a slight valve tap or knock. Accelerating will move the needle back into the 20 to 30 PSI range.

Oil pump failing? Clogged oil pump screen? Or in need of new bearings? Something else?!

What do you guys think? Any insight would be greatly appreciated

 

im shootin in the dark here but get rid of the synthetic oil. our old trucks dont need it. others will chime in who are more experienced in this matter than me

 

I am going to say your bearings are shot.

As the oil thins down as it gets hot, you loose your oil pressure.

You could TRY 15w-40 and some lucas to see if that prolongs the inevitable

 

agreed on the 15w40. alot of us use it

 

Thicker oil is a band-aid fix. Synthetic or dino oil makes no difference. You have a serious problem in front of you.

BTW...You have a 4R70W transmission. Ford never put an AODE in trucks.

 

E4od transmission. Main bearing are probably shot. 15w-40 won't hurt a thing. I have had them like this that lasted a long time. Very little oil is needed at idle. Old days rule of thumb was 5 psi per 1000 rpms. So as long as it is moving oil and you don't just beat the crap out of it. It could last a long time

 

I agree they last quite long even with low oil psi. I know! Old 302 I had would run with nearly 0 psi at idle, and I just used 15w-40 dino oil. Front cam bearings were completely toast and it sounded like a diesel. I ran it for another year or so like that.

 

High volume oil pump is the king of band aid fixes. It's more like a "splint" fix.

It can run very long with worn bearings, if heavier oil doesn't fix the issue just pop a HV oil pump in.

 

But it all boils down to the same conclusion...the engine is very tired. Thicker oil or a HV oil pump are band-aid fixes. Sooner or later it's time to pay the piper.

 

Sometimes all you need is a band aid. It is a beater and the longer it lasts the better.

 

Thanks for all the replies everyone! This is a very helpful and friendly community, glad I signed up!

I'm going to try out some thicker oil this weekend meanwhile researching how to install a higher pressure oil pump. And perhaps an engine rebuild this winter

 

To be clear, you don't want a high pressure oil pump. You need a high volume....they sell both, and there is a difference.

You'll have to hoist the engine up a bit to snake the oil pan out. I've done oil pumps blindly, with my arm snaked in the pan without lifting the engine but it is no fun whatsoever

 

my truck with a 302 was having low oil pressure at idle. I switched to the high mileage oil from valvoline. 10w-30 or 40. The red bottle. Then i put one bottle of stp high mileage oil treatment with the high zinc. My oil pressure came way back up. Was thinking about a rebuild. but working great for now.