I Have A 1990 F150 With Stock 302 At 159,000 Miles. Yesterday I Was Driving Slow Down A Dirt Road Aprox. 2 Miles From Home Went The Valves And Lifters Started Tapping. I Look At The Gauge And I Had No Oil Pressure. I Stopped And Checked I Had Pleny Of Oil. My Guess Is That The Pick-up Screen Is Clogged And Possible Oil Pump Failure. When I Cranked It Up The Oil Pressure Returned To Normal.
My Question Is Should I Replace The Oil Pump With A Regular Or High Volume Oil Pump As There Isn't Much Difference In Price. I Only Use This Truck Occasionally To Pull A Trailer With. I Have Read Where If I Replace The Pump With A High Volume One I Should Replace The Shaft From The Distributor With A Heavier One ?

 

With a high volume, I think ou also need to go to a deeper oilpan to carry more oil. Or else the high volume of hte pump will put all the oil up in the engine, then start sucking at nothing. Not sure about it..but maybe a high pressure pump?

A stock replcement from a quality manufacturer should be fine though...

 

I agree, the stock replacement would probably be the right choice. The HV pump just isn't necessary on a stock engine, and it would probably require a different oil pan/pickup.

 

While on this dirt road, were you possibly in a low gear where the engine may have been at moderately high RPM? Were you bouncing along over bumps and ruts? All of these things can cause the oil to slosh around. The pans hold just enough oil to keep things safe on the highway. One gulp of air and the pump could loose its prime. If the problem happened on the street, then I would worry. If you spend a lot of time in the dirt them consider a deep sump pan. The stock pump supplies plenty of oil, unless you build a race motor, Larger bearing clearances, high RPM, etc. Good luck.

 

It's possible that the pump is still good and the bearings just have too much wear. When your oil gets good and warm, it gets too thin and the pressure drops.

Bearing clearances directly effect the oil pressure.

 

Ideally, this guy should get a real oil pressure gauge on his motor. If the oil pressure is good (between 40 and 60psi) when the motor is cold, the oil pump/pickup is fine. If the oil pressure drops after the engine warms up, that is the cause of bearing clearances like you mentioned. This is normal on an older engine, but once the oil pressure drops down beyond satisfactory pressures (IMO below 15 psi at idle when warmed), its an indication that the motor needs a rebuild soon. My dad's 351 ran into the same issue, we put an oil pressure gauge on it and discovered the oil pressure went down to about 10-15psi at idle while warm. When you got the RPMs up some, the pressure would increase to about 35-40. After a year, the oil pressure would drop down to about 2-5psi, but still get 30-35 when the RPMs were above idle. There were only about 4-5k miles put on the truck in that year, so once that oil pressure gets low, it'll kill the motor shortly. It still ran fine, we sold it as is, so if it was a beater vehicle of mine and I didn't care about the engine performance, i'd have let it run til it actually died, but it was gettin' close.

The stock oil pressure gauge isn't very accurate, so thats why I recommend getting an aftermarket unit.

 

I would think it might be worn to the point were its not supplying the pressure it used to. I don't recomend putting a HV pump on a worn engine a stock one will surfice.

If you plan a rebuild then go with a HV, I have always used them on new rebuilds with good results.

 

You could have a oil pump rod bad ! But I would pull down the oil pan & check mains & rods . If the crank is ok I would install new bearings crank& rods &, a new pump 7 pick up also . And replace the oil pump rod with a heavy duty one [summitt] mine twisted like a pretzel year be for last.

Don

 

Definitely agree with putting an aftermarket oil pressure guage on to verify pressure.
Should be between 40 and 60 PSI with the engine at 2000 RPM. Note, the engine should be brought to operating temps and run that way for a while before taking the final reading. This is Ford Spec.
There is no spec that I know of for the low pressure at idle. I would start to worry though if the pressure dropped below 20 PSI while idling and hot. Had this situation with an 88 Ranger w/ a 2.9L V6. Once that pressure dropped below 20 PSI at idle, it was too late. Ended up with a new long block.

 

A high volume oil pump will NOT empty a stock oil pan. If anybody thinks I'm wrong, please go to the Melling oil pump website, and do a little educational reading. It's just an old wives tale, and Melling clearly states it as such.

 

Thanks For The Information. I Will Invest In An Oil Pressure Gauge So I Will Known The True Reading. It Was About 38 Degrees And The Engine Had Not Fully Warmed Up When This Happened. After The Engine Warmed Up There Was Plenty Of Pressure.