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Q: Oil pressure loss - 2005 Chevrolet Avalanche

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Hi, i have a 2004 Avalanche 5.3. . Truck has been idle for about 3 weeks while body was being redone. Picked it up yesterday and drove it about 10 miles when I lost oil pressure. Engine noisy. Changed out the oil filter, pressure good and engine quiet. I use synthetic oil. Drive later for about 25 miles, same issue again, engine noisy. Shut it down and called tow truck. In the meant time after about 10 minutes refired the truck, lots of oil pressure and quiet engine. Watched gauge it slowly began to drift down again so shut it off. Am I looking at sludge in the pan moving around and plugging the pickup or had the O ring on the tube hardened up and leaking from sitting.

My car has 256000 miles.
My car has an automatic transmission.

Hello - no, most likely this is the oil pressure relief valve sticking in the "open" position when the pressure comes up. It may then release after sitting a bit, or when you next hit the starter. The early 4.8/5.3 engines had some problems with this valve - scary! You might pull the valve, and using an oil gallery brush and some solvent, scrub the passage out. An engine sludge cleaner treatment MAY help as well - Seafoam is a popular choice, but there are others.

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