"Because of the close tolerances that are required inside the oil pump, debris of any kind can cause havoc if it gets sucked into the pump. Anything larger than the minimum internal clearances can score or jam the pump. Debris such as pieces of old valve stem seals, gasket material, plastic chips from a worn timing chain gear, bearing material, casting flashing, sand, dirt, etc., may be harmful or fatal if ingested.
But how can this kind of crud get inside the pump, you ask? The screen that is on the oil pump pickup tube in the crankcase only prevents relatively big pieces of debris from being drawn into the pump, and even then it does not always do that because most pickup screens have some type of bypass valve or vent that allows oil to bypass the screen if the screen becomes plugged or the oil is too thick to pass through the screen. The holes in the screen itself measure about 0.040 inches square, which are huge openings as far as debris is concerned. But the holes are large by design so the screen will flow an adequate amount of oil when the engine is cold and the oil in the crankcase is thick (which is why you should always follow the vehicle manufacturer recommendations on oil viscosity). All this means the oil pump is the only engine component that is continually lubed with unfiltered oil! The oil does not pass through the filter until after it leaves the pump. So any abrasive debris that finds its way into the crankcase will first pass through the pump before it is trapped by the filter. No wonder oil pumps wear out and break.
Restrictions in the pickup tube screen can choke off the flow of oil into the pump, reducing flow and pressure. Even a relatively small amount of varnish buildup on the screen can restrict oil flow at higher engine speeds. A coating only .005 inch thick on the screen will reduce the total "open" area of each hole to .030 inches, causing a whopping 44 percent reduction in oil flow!
The pressure relief valve, which may be located on the pump body or elsewhere on the engine, can be yet another cause of low oil pressure if the valve sticks open or is held open by a small piece of debris. The relief valve is designed to limit oil pressure as engine speed increases. The valve opens when pressure reaches a preset value (typically 40 to 60 psi). This vents oil back into the crankcase and limits maximum oil pressure in the engine. The reason for doing so is to prevent oil pressure from reaching dangerous levels. Too much oil pressure can be just as bad as too little because excessive pressure can rupture the oil filter or even blow out pressed-in oil galley plugs in the block.
Low oil pressure may also be the result of air in the pump. If there is too little oil in the pan, air can be drawn into the pump. But this can also happen if the crankcase has been overfilled. The oil can become aerated (full of tiny bubbles) because it is making contact with the spinning crankshaft and is being churned into foam."
J, time to drop the oil pan and check to see if the pickup screen is obstructed. Good luck...
That would be great!
