hi guys, i am new to the site but have a question about my truck. it is a 99 tahoe lt with the 5.3. when you cold crank it, the truck seems to run just fine. give it about 30 minutes to warm up and a slight knocking sound comes from the bottom area of the motor. after about 5 minutes of a light knock, it turns into a much more loud and noticeable knocking sound. The local mechanics have told me that it is going to cost me almost 3k in repairs, i need a new motor according to them. I was hoping someone may have a solution for me or if they have heard of this problem occuring before. thanks in advance

Steve

 

Welcome to the forum. It sounds like worn-out crankshaft journals and bearings. Once the oil warms up, its viscosity goes down (gets thinner) and thus can't keep the metal-to-metal rubbing from happening. You can try a higher viscosity oil but what's worn away can't be restored.