Oil Pressure problem

[Rickl210]

I have a 1999 Silverado 1500 extended cab 4.8L engine and i am having oil pressure problems i have already replaced the oil sending unit, and an o-ring on the screen tube but most importantly i have replaced the oil pump> When i start the truck i have good pressure and its stays like that for like 10-15 miles but then it drops and at a stop i lose oil pressure. Does anyone know why this might be or has anyone had a problem like this that might be able to share some insight on how to fix this? Could i have gotten a defective pump or is it something else that i am not seeing here.

[LongIslander26]

Originally Posted by Rickl210

I have a 1999 Silverado 1500 extended cab 4.8L engine and i am having oil pressure problems i have already replaced the oil sending unit, and an o-ring on the screen tube but most importantly i have replaced the oil pump> When i start the truck i have good pressure and its stays like that for like 10-15 miles but then it drops and at a stop i lose oil pressure. Does anyone know why this might be or has anyone had a problem like this that might be able to share some insight on how to fix this? Could i have gotten a defective pump or is it something else that i am not seeing here.

If you have wear in the main bearings, it will cause low oil pressure. It is entirely possible you got a bad pump. What you'll want to do is remove the pressure sending unit, and screw in a pressure test guage, and see if what that guage says jives with what the dash guage was telling you. If the test guage pressure reads good, then you'll want to look at the guage itself, or some other electrical concern.

[Rickl210]

need more feedback if any one else has info thanks for the reply

[3wbdriver]

What is it reading after the truck gets warm?

[Rickl210]

it drops to no pressure at a stop but when iam driving it reads 30 or more

[LongIslander26]

Originally Posted by Rickl210

it drops to no pressure at a stop but when iam driving it reads 30 or more

How many miles are on it? Could be excessive tolerances in the engine bearings. What weight of oil are you using? You may have to go to a heavier weight oil to keep the pressure up. You may want to try a quart of Lucas Oil treatment. Are the front crank or rear mains leaking? The back of the intake manifold? it could also be the seal on the distributor in the engine as well. If you're 100% sure the guage is accurate, then it definitely sounds like an internal engine problem.

[Rickl210]

it has over 100,000 miles on it i am using 40 weight nothing is leaking so would it be better to get a new block and crank or switch out the bearings

[HanibalTheCannibal]

Originally Posted by Rickl210

it has over 100,000 miles on it i am using 40 weight nothing is leaking so would it be better to get a new block and crank or switch out the bearings

Changing out the bearings will get you a few more years, maybe less. The crank journals are worn to a specific tolerance (ie scratches and marks) and your new bearings will not compensate for this. The crank will wear your bearings quicker and you run a chance of throwing one out. I swapped main bearings on an engine that needed an overhaul, it got me 3 years. Then one day at 70mph the engine locked up. (I knew it was coming and I welcomed it )

The time and money involved in switching the bearings could be used to get you a nice GM crate engine (or a nice comparable rebuild).

My vote is that you get a fresh engine VS changing beearings. It sounds like you have done everything you can.

[pies]

i agree , hook up a mechanical gauge to verify that the dah gauge is reading correctly. main bearings and camshaft bearings can cuase this problem. when it loses its oil pressure leave it idling for 5 minutes, if the oil pressure is low you should hear the lifters start ticking. you can pull the pressure regulator out of the oil pump and check to see if the spring is broken, but with a new pump i don't think that this is your problem.