I have a 99 silverado 1500 z71 with the 5.3. I have been hearing this knocking noise at first start, but hasn't really worried me because of what everyone has said about it, not that big of a deal. I was talking to my mechanic friend and i mentioned i had been burning coolant(about a jug a week), the knocking, and a little hesitation when i take off in the morning. He said that the heads of these motors are famous for cracking. So my heads are cracked and instead of just fixing the heads of a motor with almost 200,000 miles i was thinking of buying a long block from somewhere. I've looked at em from autozone, oreillys, rock autoparts. The manufacturers of these motors are Marshall engines, powertorque motors, and sunfire or something like that. I havent dealt with these motors before and i'm wondering if any of you have. I don't want to buy one of these long blocks if im gonna have problems in 30,000 miles. I appreciate to hear what yall have to say

 

Do you know for a fact that the heads or cracked? Or just goin off what the mechanic said? I'd just go to a junkyard, find a 2500hd or escalade and get the 6.0 v8, harness and everything for like 800 bucks. Get a tune and drive on with that extra power