Ok well i bought the 87 f150 300 6. The truck has alot of new parts and looks great I test drove it for about 20min twice before buying it, climbed all under it looked good. Now when u crank its 50psi oil pressure, drive it 20-30 min. 40-50psi after you drive longer the pressure starts dropping to around 25psi if I let off it builds back up to 40-50psi give it throttle back to 25psi...... but then when I stop to idle it reads zero...it has both factory oil gauge and mechanical oil gauges the mechanical is the one I watch the most when it reads zero the factory gauge is still showing normal... no sound change from the engine.... When the mechanical gauge said zero I got out while its running and looked down in the oil cap and it seems to still be oiling....any suggestions

 

If a mechanical gauge said zero, then you really are in trouble (assuming it's reading right). Start by pulling a rod and main cap and inspecing for damage. If they are ok (chancy on a 87), then try a new oil pump. Otherwise, it's loooking like an engine job.

 

i was afraid of that...thats why i test drove it twice but it was only 15-20min worth so it looked good the whole time....it has 180k on it and from reading about them thought i was doing good....should have drove it longer.....guess ill be buying a 300 6 book....i probably should put it up for sale too lol.... its just it looked so good and taken care of thought i was alright....

 

why not listen to the engine at idle and see if you hear the tapping of the lifters that's the sure sign of low to no pressure. if no sound then replace the pump and pick up screen and check for sludge in the bottom of the pan. those engines were and still are the best engines for six bangers ever made

 

I just had thought this might help you out a little bit more get a quart of diesel fuel and add it to the oil to clean out the return ports in the block and if you do this don't rev the engine with diesel fuel in the crank case it will blow it up. I have a feeling that all the oil is staying up top and takes it's time getting back down into the oil pan. you will have to change your oil two or three times to get rid of the diesel fuel completely

 

Thanks for the suggestions...After running it and getting everything nice and warmed up gauge reading zero the engine sounds just as good as it does with 50psi. Its confusing to me I should hear something change you would think...I thought about and thought about it and called the man I bought it from and he said it done that to him for 3 yrs..and he had forgot about it (lol)..He also said he believes he over tightened the compression nut down at the oil sending unit and could have collapsed it some...Havent had time to check it but I wouldnt think that would make it act like it does..

 

All of these engines are a little picky on their oil pressure and you run the risk of running out or too low of oil. I would just keep a close eye on the level and drive it till it quits

 

I was getting stressed out over it, but like you just said keep an eye on the oil and driver her till she dies....I had called around on some reman engines..names like powertorque, atk, marshall, sparton, have you ever heard of these brands? They all had the 36mth warranty.... Just trying to get my ducks in a roll so when and if it does blow what would be the quickest way of getting it back on the road.

 

before you get yourself all strung out on this, why not replace the sending unit, line, and guage first? if the electronic guage is showing close to normal,and the mech. guage is way different one of the two aint right.

 

if you feel that you need to replace the engine then why not get that one rebuilt before it blows or gives you all it has. it may have already been done for all we know. I wouldn't worry unless you're going down the road and both read no pressure.