what will cause low oil pressure on startup and idle but will get around 40 when the engine warms up 05 5.3 silverado

How many miles is on engine and how low does it go, and how long has it been doing it, and how many my miles on your oil change, are you using the motor that is recommended in your owners manual or on your oil fill cap, and keep it full. Thank you Dennis

it has been doing this about month or so. oil is correct have kept it changed around 3000 miles truck has 175000mi. it will fall back and forth at idle and once you give it gas it will go to 40 and the warmer the temp the better the pressure. sending unit is new and checked pressure with a gauge it read the same

You checked your oil pressure with a gage, good, you have 3000 on your oil, I would go ahead and change it, do this, get a clean glass bottle, with the engine cold, clean around the drain plug first, drain the first part of the oil into the glass bottle, let the glass bottle set, overnight, if any of the oil separates, if so that's not good, let me know the color, Dennis

have the oil change every 3000mi. just had it changed yesterday. I was thinking oil pump or screen problem . there shouldn't be any reason for the screen to be stopped up but you never know.

thanks

Do you still have or can you get the old oil filter Thank you Dennis

I am having the same issue with my '05 Tahoe. Are you looking for coolant in the oil? Was this ever resolved?

To start with, were are you living, what state, are you having severe cold weather, be low or near o* fahrenheit, do you know what weight motor oil is in you car, how many miles is on your car/ if engine has been replaced or rebuilt, and how many miles has it been since your last oil change ? please check and advice Thank you Dennis dennisjf12@gmail.com

Be aware there is a small oil screen inside the hole below the pressure sender on many chevy silverado's. Remove the oil pressure sender, use a small pick tool to pull the filter from the hole, replace with a new filter. These tiny filters will clog, and cause low pressure warnings, and or wild variations in pressure as engine rpm's increase.

What ended up being the solution?? I have the Exact same problem on a 99 Silverado 5.3L. The colder the worse it is so I would believe it is a suction problem. I haven't verified with another gauge but it acts normal once pressure is achieved. Cold starts (<30 deg F) it can take up to 10 seconds to build pressure. Also can see a slight fluctuation (~2psi) at idle. It has the correct oil in it (5w-30). And have changed it once since noticing but problem persisted. I changed the oil pan ~9 months ago and changed the take up o- ring at that time. Once complete oil pressure was perfect 40psi at idle and up to 60psi under load. So I figured everything was gravy. Maybe I didn't quite torq the take up bolt enough and it has walked? If I don't hear back I'm gonna go ahead and change the oil pump and take up o-ring and keep my fingers crossed. Any help is appreciated! -Matt

check the o ring on pick up tube if it is worn it will allow some oil to drain past the outside of pick up tube causing low oil pressure at idle.

Had this same problem with my 08 Suburban LTZ. Cold start it would run at about 10psi and would immediately begin to drift down to 0psi. Long story short, we dropped the front axle and oil pan( which takes half the time of pulling the oil pump) and replaced the worn oring in about 5 hours. Now cold start idle produces 60psi and the same pressure at highway speeds once warm.

So what is the answer

Also wondering what the answer ended up being. My 08 Silverado with 183,000+ miles just threw a low oil pressure light after backing into driveway from a 10 min drive. Oil pressure is great at 1,500+ RPMs, but it threw the light as I threw her in park and she started idling at about 500 RPMs. I cleaned MAF sensor and air filter to try to resolve a left bank lean engine light. The engine light remains but the oil pressure stays steady and rises and falls accordingly with RPMs now. Not sure if it was a fluke warning with a fuse acting up or what. Would like to know what worked for you. Heard too much clearance in higher milage engines do this and often require overhaul. Maybe I can talk the wife into an AFM delete and truck Cam upgrade kit.

2007 Tahoe with the 5.3, 90000 miles and it gives "oil low" every 4000 miles or so and I add a quart (these engines with the AFM are known to burn some . Driving two weeks ago and got "low oil pressure, turn off engine", the alarm, red light etc. luckily I was close to a Valvoline quick lube and they said it was down 1.5 quarts. Changed the oil, filter, etc. and that seemed to fix it. I think I waited too long to change it so the oil was low and the viscosity was too low?

Get a tune and delete the afm, it will take care of most of the oil consumption issues