Oil Pressure Drop & Fluctuation???

73 1/2 ton pickup with 350 engine ;
upon start up I get right at 50psi oil pressure. After warm up, I am getting 30psi at idle and 45psi at acceleration.
No problem there, however when she has been driven for some distance the oil pressure falls to near 1 psi and sometimes it will bottom out at 0psi when stopped at a traffic signal. The pressure will come up by increasing rpm, but it is still very low (around 5psi). The pressure will come back up to 30psi again while driving .
I have a mechanical pressure gauge installed so that i can see what the "real" oil pressure is doing instead of the electric guage and sending unit set up.
The oil and filter was changed to rule out oil break down or gasoline thinning, but it did not change a thing.


my first thought is oil pump failure, but cant really decide if that is what the cause is or not since it has such good pressure at start up and while driving, & evidentally it is getting atleast some lubrication to the top of the engine since i dont hear any lifter chatter

what else could be the cause of this pressure fluctuation or can the oil pump still be bad & vary pressures in this manner after the engine & oil gets hot? (I know oil pressure will drop some after warm up , but this is an awful wide span of variance and seeing 0 to 1 psi can't be good)

it might be youre oil pump. mi friend hade the same problem on hes 2000 denali and it's working properly now but if you replace it dont buy a gm
buy an after market one i wonder what chevy was thinking wen they
put dose pumps in. I have the same problem with my LT1 just like yours
one day i was racing with my friends and i sen my oil pressure drop to
zero i got the check guage i stop accelarating and the oil pressure went up
again i might change it with a high pressure not high valume

I have a 78 1/2 ton short bed this trucks are awsome did you make any mods to youre engine?. i rebuilt my 350 put in a cam from edelbrock performer plus not the rpm i put an intake by edelbrock some hadders and a 700 R4 tran it's all it takes to make them fasti was smoking 5.0 mustangs by half car to be a truck thats alot now i replaced that 350 to a 454 it's on the truck but i havent started yet the 454 is stock right now but i bught a comp cam cam kit edelbrock air gap intake headman headders 850cfm holley double pumper high flow water pump a 50,000 volt dist. msd ignition a holley fuel pump electric and i updating my front to a 1991 suburban. thats sweet i love this trucks

when your engine is cold the oil is also cold .... which means it going to be thicker right???? when the oil is thicker it creates more resistence as it being "pushed" through the engine. the very first place that the engine pushes the oil too is the main bearings on the crankshaft. also at the time of start up the main bearings are also cold. when something is cold it contracts when its hot it expands. so.. when the engine first starts the mains are "tighter" around the crank... and the oil is also thicker.. when it warms up the mains bearings expand giving there more clearence between the bearing and the crank as well as the oil is becoming thinner . so the restence goes down. which means lower oil preasure... the gauge must be working do to the fact when the rpm goes up so does the oil pressure. make a long story short..... mains probably need to be replaced!