If it's a 5.3L it may have defective heads on it. GM had heads that wept through the casting where the oil drain areas where. I had a set of those on my 2002 silverado. Although it wouldn't show up in the oil over about a month it would empty the overflow tank and a little out of the radiator.removal of the valve covers and pressure testing is the only way to find it. If they leak GM will not warranty them,although there is a tsb out about them. I done a engine swap crate engine to be on the safe side@117,000 and it also had the heads on it. Dealer got head castings only and had to send them out to a machine shop to transfer everything from them to the new heads.The marking on them is a small parallogram under the valve train.
Sep 23, 2010 at 7:14 AM
