hi I have I 98 blazer 4 door 4.3 and over about a years time my oil pressure has went from about 40 at idle, 80 while driving after heated up, to 20 at idle and 40 while driving. my pan gasket leaks very slightly and my intake gasket is a bit oily so maybe that could affect pressure. I was also told that it may be a rear main seal. I would imagine that if any gasket in the engine is leaking that there would be somewhat of a drop in oil pressure. seems like common sense. if you have had this problem, I would greatly appreciate any good advice. thanks!

 

the oil in the pan isnt pressurized. that would suck cause any kinda pan leak and stuff would be splattering all over the place.

20idle and 40 running really isnt horrible. thats about what most my trucks are at. could just be a faulty gauge or sending unit bouncing around.

 

Oil pressure is made by the clearance in the main berrings... Oil pump just moves volume, it doesnt make pressure.

The only way to know for sure is to remove the oil sending unit and plug in a manual gauge to see what the reading is. As said above 20/40 aint bad, but is definately a sign of an engine thats getting tired.

There is no pressure in the crankcase, thats why an engine has a PCV valve (Pressure control valve) to releive the pressure made by pistons going up and down... If there was pressure inside and engine you would blow the pan gaskets out.

When oil pressure is low, its cause the engine is on its way out. The only fix is new main berrings - which are part of a rebuild.

The oil pump is kind of like a running hose. If you stick your finger on the end, you still get the same amount of volume, but you get pressure too. Its the small space that the oil is being pumped through that makes the pressure. When that small space wears out and gets bigger your pressure drops off.