i was driving along the other day and noticed my oil pressure was down a LOT. i stoped bought a couple quarts of oil knowing the truck uses some, added two quarts and still have really low pressure. on my way home from the parrt store the pressure droped completly several times but i never heard the engine knock or any ussual noises, any idea what it could be.

ps the truck is a 1991 F-250 351w 5 speed,

 

What gauge were you using to determine the oil pressure? I'm not all that convinced that the factory oil pressure gauges (dash gauges) are all that accurate. The first thing I would do is get a good mechanical gauge and check the pressure. I'm sure others will chime in here with other things to check.

 

gauge in dash is an idiot lite, it drops if it gets pressure less than 7 pounds.

get mech gauge and check to see if you really have a problem.

could be clogged oil pickup screen.

you neglected to say how many miles on motor.

 

i was going by the factory gauge, since that was the only gauge in the truck. the truck has 174,xxx but the motor has 50,000-60,000 miles i believe.

i put a mechanial gauge in tonight and the pressure seem good, 50 psi at around 2 grand fully warmed up. the haynes books says 45-60 i think

 

the sender was/is probably bad.

some members get a t-fitting so they can have the dash gauge and a mech. gauge.

 

What is the pressure at warm idle?

 

You can get a real gauge sender (as opposed to a switch sender) at any parts store. That's what they usually sell. It will read back an actual level on the dash gauge. Obviously, no numbers, but it's still quite useful and easier than running a pressurized oil line to a retrofit gauge.

 

I would recommend you replace the sender. I had the same issue with my 5.8 the oil pressure always read a little low then it started to drop to nothing and the CEL came on. Changed the sender and pressure remains steady all the time now.

 

and the sender is cheap too btw

 

Old thread but I did not want to start one.

88k miles

New sensor.

Fluctuates from nothing to a happy middle.

The stock gauge is horrid.

I am going to install a mech oil pressure, but first and foremost; what range gauge?

Where to tap?

Thanks.

Nm Gonzo

 

What engine? My 302 has a port above the oil filter. I think it's a 1/4" NPT.

I think a gauge that reads up to 80 psi should work. I think mine reads 60 psi normally, with a new pump.

 

1988 5.8

Sorry .... forgot.

 

The mechanical gauge should have a fitting which replaces the original sender, unless you add a "tee" fitting which allows you to mount both. The sensor should be on the front driver's side, above the oil filter IIRC.

If your oil pressure is low, you will start hearing lifter noise, a "tick-tick-tick" with engine RPM.

The way I heard it, the common problems are leaking main bearings which cause oil pressure to drop to nothing at low rpm, and your lifters will make noise, but it builds up pressure and is ok at higher rpm. Replacing the bearings is most of a rebuild so this is serious. But, it's not unusual for oil pressure to drop a LOT at idle anyways.

The other problem is oil pump inlet screen gets clogged with debris from the coating they put on the original timing chain sprocket. Some said it's fiberglass, other said it's nylon, either way they said it was intended to quiet the chain.

Or the oil filter could become clogged in very odd situations, but it's easy to fix.

IIRC, the oil pump itself seldom "wears", they say. However, the pump's driven by a drive shaft from the distributor that sometimes breaks, which will only result in NO pressure at all and it can't be driven period.

 

There is oil pressure , but is vague.

I am looking right now for the coupler thingy so I can have both gauges working.

 

There's no need for the inferior "electronic" gauge if you have the mechanical one. The tee and sender unit will only reduce the clearance around the engine while doing stuff on it, and present another point where a leak might occur.

I do worry about that plastic hose catching on something and getting busted, which might mean you'd be stuck because it'll spew oil when started. Vice grips MIGHT enable you to get home. I threw the old sender in the back so IF that happened, I could just remove that fitting that goes to the tube and use the sender to plug the hole.

IIRC I had trouble with the gauge going up and down randomly due to a bad connection, and due to the slow action of the dash's gauge, it looked like it was following something going on in the engine rather than being static noise.