Hello all,
I have a 95 f150 302 v8.
oil pressure has gone to zero. It is not the guage or sending unit causing the problem.
When I first crank it up it has good oil pressure then when it warms up the pressure falls off and the valves start clattering.
I ran some engine flush through it hoping to clear a clogged line or oil screen.
I let the flush stay in overnight to really soak the screen on the pickup tube.
I drained the oila nd put in new oil and filter. Then I cranked it up and let it idle for about 20 minutes and had good pressure, more than ever before.
As soon as I put it in gear and drove about 300 yards the pressure fell of to zero again and valves started clattering.
I pulled the oil pan and filter. The filter had hardly any oil in it.
Should'nt the filter have been full after running for 20 minutes?
Also the dipstick showed about a quart over full while engine was running.
What's up with that?
Is it a fair assessment to say that the pickup tube is clogged and not letting oil get through?
Think about it:
1. Oil filter had almost zero oil in it when I removed it
2. Even with engine running the oil level on dipstick showed the same as when not running

Also, I could not get the oil pan all the way off and could only reach in and feel the pump and screen. All I could feel on the screen was what felt like a solid metal cover on the bottom and nothing that felt like screen. Does the filter on the pickup tube actually have a mesh screen or is it a metal cover with tiny holes in it?
Do I have to remove the engine to pull the oil pan?
Thanks everyone for response.

 

I have reread this twice...but it still sounds like the pump. How long of a period are we talking about for your oil pressure to start acting this way? I don't know the 302 very well,maybe somebody can enlighten us?

 

How long have you ran this motor w/ no oil pressure?

You have to lift the motor about 2" to get the pan off with it in the truck.

Sounds like you need to take a good look at the pump and pickup for a blockage...

but my main concern now is not that...but rather how long this engine has ran w/o oil pressure. If you got any RPMs on the motor w/o oil pressure...and a bunch of idle time....in addition to the fact that it's not a new motor...I'm willing to bet your engine would probably be toast. Those bearings would be chewed up if you ran it too much. If you havn't, don't!

Do you still have the stock oil pressure gauge/sending unit on it? If so, put a real oil pressure gauge in it so you can actually know...the stock gauge is practically useless.

From this point on, I would not run the engine or run it only if there is adequate pressure. If needed, I would go to autozone and rent an oil pump primer...this way you can take the distributor out and use a drill to spin the oil pump w/o running the engine.

1. Put a real gauge on it
2. Start the engine and check pressure. Should be 50-60psi cold startup and you should get that pressure within 2-3 seconds of starting it. If you don't, take note of what you have, if it's under 10psi..shut it off. It will normally go to 20psi when under hot idle...and 10psi per 1000 rpm under hot driving.

If that spec isn't met...

1. Worn engines have seemingly good oil pressure while driving but drop pressure at hot idle (below 20psi). If that is the only thing that occurs...IE...you have good pressure except it drops at warm idle...you've simply got a worn out engine and it needs to be rebuilt soon.

2. If the oil pressure doesn't meet the spec and it's fairly random (drops low when it should have more pressure)...than it's probably the oil pump or clog in the system.


Since you said you don't get a lot of oil in the filter and it sounds like you're not getting a lot of oil at the valves...I'd say you have some kind of oil system blockage problem that you need to take the oil pan off and check the pump and the pickup...

 

I wouldn't bother with a real pressure gauge. The stock gauge does what it is designed to do, tell the driver when there is no oil pressure, and it is doing that just fine. The no oil pressure on the gauge seems to coincide with the lifter noise in the engine. Zero pressure is going to look the same on the stock gauge as it would on an aftermarket one. Drop the pan and see what things look like, and if the pickup screen and everything else looks ok, give replacing the oil pump a try.

 

Your are correct, but a real oil pressure gauge is more reliable, cheap, easy to install, and gives much more accurate readings. The stock gauge will basically tell you two things...if there is pressure or if there isn't. It won't tell you what level or pressure is there...which is important when diagnosing an engine related problem such as this. You cannot see fluctations in pressure or changes in pressure on a stock gauge.

 

you say you pulled the oil pan and filter, did you really drop the oil pan already?

you need to fix either: oil pump, clogged screen, clogged oil drains or broken oil pump shaft.

 

Justin I know that real pressure gauges are better, but zero is zero, no matter what the gauge. A real oil pressure gauge will do no good in diagnosing the current problem. Spend the money on fixing the problem, then if you want to see the real oil pressure, buy a gauge.

 

Not to be argumentative, but zero oil pressure isn't the only thing we would want to know here. I'm sure you could get away without using an oil pressure gauge but IMO it's worth the $30 or so...if he doesn't want to than he obviously doesn't have to...

The thing is we're not just trying to find out if he has no oil pressure or some oil pressure...we also want to know if the pressure is fluctuating improperly and that would help indicate the area of the problem (blockage or oil pump problem) or worn bearings, etc.

If he doesn't have a real oil pressure gauge than he doesn't know whether or not he has appropriate pressures considering we are having oil system trouble. A real gauge offers peace of mind and assurance of a properly functioning or malfunctioning oil system.