Question: I have a 2001 Chevrolet Tahoe with a 5.3-liter engine, 127,000 miles. It runs great and the oil pressure is terrific, but it has an inconsistent hydraulic noise when first starting and shortly thereafter. I have changed the oil twice and it seems to be better.
| Truck Trend Garage Noisy Lifters
Answer: A few years back, we had a lot of questions regarding the cold-start piston knock from several GM-built engines. The bottom-line answer was that it's a normal characteristic of the engine and will have no long-term effect on performance or durability. It was actually a piston design flaw, which caused a knock after about 20,000 miles due to carbon buildup. The pistons in newer engines were redesigned to eliminate the noise, but those who bought the prototypes had to live with it. You can bring your Tahoe to a Chevy service department and leave it overnight. I'm sure you can avoid any diagnostic fee for just a cold-start confirmation of the knock.
But you do state it was a hydraulic (hydraulic valve lifter) noise, which typically describes a "tick," not a knock. If that's the case, there may be an oil aeration problem. This tick is usually noticed when the engine is new, and is caused by a factory split in the O-ring that seals the oil pick-up screen to the oil pump. This requires removal of the oil pan for inspection and replacement. Again, a dealership technician can most likely identify the noise with a quick listen.
If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 831 S. Douglas Street, El Segundo, CA 90245, or e-mail us at trucktrend@sourceinterlink.com. Please include the VIN with your question. Due to the volume of questions received every month, we cannot guarantee that everyone's question will be personally answered or will appear in the magazine.
Can't wait for help with a problem you're having with your Truck or SUV? Ask the expert we trust here at Truck Trend Garage -- visit Alex Steele at www.RealWorldAutomotive.com.
