I have a 91 F150 with a 300 straight 6 in it. Recently I noticed that when it gets to operating temp the oil pressure drops and it sound like a diesel when i get to the end of a gear or feather the accelerator. It has 250,000+ on it. Could this old girl be getting to tired?

 

id like mine to sound like a diesel lol.... i would think you can get another 50,000 out of it anyway!

 

Yeah but to what expense. I hear people say "main bearing",Cam shaft bearing", "Water pump" ect. I dont even know where to start exept a mechanic$$$$.

 

Probably rod bearings. Rod bearings just getting a bit too worn can do what you describe. Low oil pressure is also consistent with worn rod bearings. (or any bearing for that matter). Main bearings will typically make a scratchy screeching noise, rod bearings usually knock.

If it is rod bearings and you replace them quickly before it gets any worse, they may be all you would have to change. If you keep letting it knock, it will start to hammer the crank out of round. Eventually you'll hammer the rod cap right off and your engine block will have a new hole in it.

However, start with the basic stuff. Let it get warmed up, and then take the serpentine belt off and take it for a quick drive (before it has a chance to overheat) to eliminate any accessories that could possibly be making the noise. If the noise goes away with the belt off, than you know its one of your accessories making the noise.

 

Thank You for a starting place I'll do the ' belt -off ' check. If it is a rod bearing am I in for a long weekend or is that a fairly simple fix? I'm jut now getting into older trucks and have always taken my vehicles in for repairs.

 

well you got 2 choices if its Rod bearings.... pull the engine and put it on a stand or 2 pull the pan with it in the truck and change them that way neither are super easy but both have pro's and con's....

 

with that many miles it would be time for a rebuild , try putting a oil pump in first ! to me your wasting your time and money on rod and main bearings with out turning the crank and resizing the rods !

 

If it's rod knock, it's too late for a new pump. The damage is already done. Often times if you catch rod knock quickly, just new bearing shells will do. You can plastigauge the new bearings to confirm.

 

no one knows for sure what it is , the lifters are one of the first things to clatter and with no or low oil pressure a new pump can fix that !
now as for the rods plastigauge will tell how much clearance and nothing else ! if the rods knock even a little the will hammer the journals and make them out of round and you cannot see out of roundness with the naked eye !
like i said it is a wast of time and money to new bearings on old and wore out parts !