low oil pressure:(

[1970 C10 MJW]

I bought an 03 tahoe lt 5.3l flex model in August I put over 10,000 miles on it since then. strangely every time I have changed the oil my pressure has gotten worse until the most recent time its now showing under 10 at regular temp on idle, mind you i have even gone to a heavier weight oil and have changed my oil pump with no change in pressure... I am pretty sure I have a bad main bearing, just want to see what other guys have to say, I am obviously no longer driving it (before you guys ask) I did change the oil pressure sender and I had a buddy with a super fancy computer scanner check the pressure from the obd2 and it confirms dangerously low oil pressure.

[Special-Ed]

just hook a manual gauge to it find out for sure

[buddy_1]

Cast iron or aluminum block?

[1970 C10 MJW]

i know the pressure is low, but thanks for the input cast iron

[1970 C10 MJW]

Sorry not trying to sound like a jerk lol, but i know its low,and its a cast iron block

[buddy_1]

There is a pressure relief valve in the oil pan just above the oil filter that can release pressure before it gets to the sensor. Is the engine noisy or just low pressure? Checking specs in Service Information shows:

•Oil Pressure – Minimum – Hot
Metric
41 kPa at 1,000 engine RPM

124 kPa at 2,000 engine RPM

165 kPa at 4,000 engine RPM

English
6 psig at 1,000 engine RPM

18 psig at 2,000 engine RPM

24 psig at 4,000 engine RPM

[1970 C10 MJW]

makes a lifter tick, and how do i check/replace that valve?

[buddy_1]

Well I think I have to correct myself, the 03 doesn't show the valve I mentioned before. It's used on the engines with Active Fuel Management. When you replaced the pump did notice a hex headed bolt/plug above the oil filter inside the pan?

[1970 C10 MJW]

i didn't drop the pan, I also do not have AFM

[buddy_1]

Well one thing that can cause low pressure would be a pinched or damaged pick-up tube o-ring/seal.

[1970 C10 MJW]

the pickup tube i believe is ok because it had good pressure before, and the seal was replaced when i changed the pump, the pressure shows the same now as it did when I had the old pump in

[buddy_1]

OK when does it make the valve train noise?

[buddy_1]

All the time, worse at certain rpm's?

[1970 C10 MJW]

always, when its cold with a lil higher oil pressure its a lil quieter...

[buddy_1]

Is it counting any misfires?

[1970 C10 MJW]

no misfires

[1970 C10 MJW]

oh and i just changed the lifters about a week before i changed the pump

[buddy_1]

All you can do now is plasti-gage the crank bearings. I have had some that the cam bearings caused the same symptoms. That's why I asked about the block earlier, I had one with aluminum block that spun #3 cam bearing out of the block. How many miles on this motor? Just remembered another one I had that acted like yours that had a lot of loose carbon floating around in the pan. While it was running the pump screen would slowly stop up with the carbon. Cut the engine off for 5 minutes and it be good for a few more minutes.

[buddy_1]

What did the rollers on your old lifters look like?

[1970 C10 MJW]

130,000 and its when the blocks warm, if i leave it sit for 2 hours the pressure will still be low, and like i say ive changed the oil a few times so i figure stuff in the pan would be gone, i use castrol syntec and k&n oil filter first time, mobil 1 filters now

[1970 C10 MJW]

the old ones looked fine

[buddy_1]

Time to pull out the plasti-gage to see how loose the crank is. Just be careful, got a feeling your gonna need cam bearings also.

[1970 C10 MJW]

thanks buddy thats what i was thinking bout the mains

[buddy_1]

Hope I was some help, let us know what you find. Good luck. Buddy

[1970 C10 MJW]

sure will