Fluctuating oil pressure at startup

[Carlos Bustamante]

I have a 2008 Chevrolet Tahoe Z71 4x4 with 170k miles. Its been a great vehicle and we plan to keep it till the wheels fall off! Last winter when up in Colorado I went to start it and the oilpressure fluctuated back and forth between 15-40 until it warmed up. When I revved up a little of course the oil pressure went up. When it was warm it idled at 30 psi and when driving 40psi and above.

When back in New Mexico I took it my mechanic and he said that the oil sending unit and gauge were fine as he checked them through the computer. He did not check it manually. It continued to fluctuate during cold startups but never to the point of throwing a check engine light, low oil pressure light, nor did I hear any engine knock. Through this Springand Summer it was fine at startup. Now its getting cold and its starting to fluctuate again on cold startups. I asked another mechanic friend about it and he says its the sending unit....that he sees them a lot with 150k mile 5.3 and 6.0 gm engines. He said its not the O-ring.....I am at a lose as with the research that I have done its looking more like the O-ring on the pickup tube.....

Any input would be appreciated!

 

[kbuskill]

I would change the sender first as it's the cheapest/easiest.

 

[Big Mama]

Agreed with K keep in mind cool weather means thicker oil and the slightest loss in suction creates lower pressure. Try the easiest first and if that’s not it go to the pickup. These engines don’t require a ton of pressure to run well but it would worry me too

 

[Carlos Bustamante]

Thanks guys, I ended up replacing the sensor first and no change. I went through and changed the O-ring and pump. Pressure now at startup is over well over 40 and it stays at 35 and above when warm. No tapping noise at all!! I am hoping to get another 175k+ out of her.

 

[dnt1010]

Same issue for me 2009 Tahoe 4x4 Hybrid 6.0 with 256k miles. low oil pressure on cold mornings and fluctuating oil pressure gauge. It shutdown yesterday morning (mid teens temp) during a remote start and threw a PO152 code. I have of course been searching for hours on the internet trying to convince myself that it is NOT the oil pickup tube ORing. Sigh, now I have pretty much accepted that most likely that is the issue and it is going to be a real PITA to do get it done..... Like most everyone else though I guess that I will change out the oil pressure sending unit and the little screen below it first since it is mush easier and there is this small remote chance that this could be the problem..........