My 2002 chevy silverado makes a knocking noise when i first start it up after it has been sitting over night?

my 2002 chevy silverado makes a knocking noise when i first start it up after it has been sitting for about 4 hours. The knocking comes from the bottom of the motor and only lasts for about 15 seconds.|||The first things to check are which oil filter and weight of oil you're using. An oil filter made by someone else, even a good company, may not be quite right for your vehicle. If, for example, it doesn't have an anti-drain-back valve, your oil passages could be empty after sitting a while.





Check the 8th character of your VIN # on the front of the drivers side of the dash, by looking through the windshield. The proper AC/Delco filters for your truck are as follows; W=PF47, V, T, or U=PF59, G=PF454.





As far as what weight of oil you are using, GM recommends 5W-30 weight for most circumstances. 10W-30 is OK if temp is always above 0 degrees F. If temp drops below -20 degrees F, Synthetic 5W-30 or 0W-30 is OK. Heavier weight (higher numbers) oils are not recommended.





Of course, these recommendations are for newer, low mileage vehicles. If you have say 100K miles or more, you may want to go one weight heavier. Many people also advise against switching to synthetic oil for higher mileage engines. Many people have their own preferences as to what brand. I like Castrol best, and BMW actually recommends it in their owners manuals.