I am new here so I hope this is the right way to do this. I have 02 4.6 160k the front of motor started ticking then oil pressure light came on so I parked it. Very long story short replaced ( Timing chains, gears, tensioners, oil pump, rod bearings, valve guides couple pistons six valves and cleaned the crap out of everything. Even those tubes in the back of intake. I learned my lesson with the oil gauge that is not an oil gauge and put in a real oil pressure gauge. So I start it up and all is well for about five minutes then the pressure starts to drop on gauge and around five pounds light comes on and i shut it down. I wait a couple minutes and repeat about five minutes oil pressure drops. All the head ports were cleaned so its not stacking up there ( I looked anyways) I am using 5w-30 pennzoil with Motorcraft filter and sending unit is new. What is left to check I am clueless.

 

Loose or plugged pick up tube, maybe even the pump.

Just guessing though.

 

It has great pressure at start up 80lbs or more then takes five minutes to taper off at that rate it would have cycled through a few times. I did run a bottle brush through it and cleaned with carb cleaner new o-ring on new pump. I even changed oil and ran it through filter to see if i missed anything after first run.

 

You got me. Maybe someone will chime in here soon.

Good luck

 

Sure SOUNDS like it's stacking up somewhere. I would have someone else on the inside and with the hood raised and set to move, I'd stab the dip stick IMMEDIATELY. If it is somehow stacking up, you shouldn't be showing anything on the stick. It's hard to imagine anything else with 80 lbs at start. How did the old parts look? ALL of them?

 

When you say new "0" ring on new pump are you refering to the "0" ring that installs on the end of pickup tube itself, the end that is inserted into the oil pump? Just thinking that if the original "0" ring was left in the old pump and you were not aware one was needed that could be your problem. The pump will suck air and lose its prime.

 

The more I think about it, at 80 lbs that baby is moving some oil. Isn't there supposed to be a by-pass around 45-65 lb range?

 

No, 80 lbs is not abnormal on cold startup. Another thought is if the pickup tube is not secured at the main cap stud it can slowly pull its self down (suction) to the bottom of the oil pan and stop oil flow.

 

I dropped pan and ran hand down the tube all seemed well. Napa gives you a shiny new red o-ring so you dont miss it on pick up tube. I was thinking it has something to do with main bearings after all i have changed everything else.

 

Lets see starts up normal and 80 PSI warms up and always drops to 5 PSI. Worn out crank and main bearings probably. You can check your pump and pick up tube. Pulling air in would create poor oil psi. Foam should be in the pan and the stick should look over full by and inch or more with engine hot. Main bearing caps come off ( check the rear one first ) Bearing will be missing its first layer and the journal may catch your fingernail with wear. Fix is to turn the crank and new bearing all around it. The real problem to deal with now, is the engine ran with awful oil psi for how long. Are the cam journals also loose? Jasper time probably? The happiest ending. A warranty motor instal. Double check the O ring visually, it may be torn. Other thing is the sender may be malfed. A reall winger that one.

 

Okay I was not going to let anyone know I did this but I live on long country road and took it for test drive and oil pressure dropped to zero so i shut it off and coasted from fifty to twenty mph then started it back up and OP jumped back to fifty and I got a few more miles and repeated. If crank and mains were bad it would not cool off that quick and tighten up around crank to build oil pressure.

 

The rod bearings looked good when I changed them but I guess mains are next. In hind sight should of pulled motor and bench built it. I will keep looking but thank you for all the help.

 

Does it tick really bad when oil drops to zero? If not maybe your oil gauge line is getting plugged? Next time its hot take it off and blow it out and try quickly.

 

I would agree 6jeff6 now I don't think its the engine and I really doubt its the mains. It sounds more like the gauge/sendor is jacked up. If no engine noise when the pressure drops then suspect the gauge. Install a manual gauge and see what pressure you get.

I mean a hydraulic oil gauge not manual...Remove the oil passage allen plug at front of the passengerside cyl head and attach the gauge there.

 

What about the oil filter bypass??? Could get hot and/or high pressured and release. When pressure drops, re-seat. Just a guess based on everything now is very tight and sealed - driving the pressure higher then before.