My name is Rob and I have a 1998 GMC Sierra 1500 4WD, 5.7L Vortec, Z-71 with 80K miles. Last Sat I started it up and white smoke bellowed out the left tailpipe. I suspected a blown head gasket. Took it to the garage and they confirmed. Repair claim consisted of gasket replacement, turned both heads, new bolts, plugs, oil, coolant. I picked up the truck on Thursday, drove less than 2 miles and with no warning a loud knocking sound came from under the hood. I immediately pulled over and inspected to find a puddle of oil under the engine and a rod protruding from the oil pan. I am almost certain that this problem is a result from something that wasn't repaired correctly when the head gasket was replaced. Can you please provide insight as to why a rod was thrown after only driving less than 2-miles at low speed. Your prompt reply would be greatly appreciated. Thank you much!
Most likely, the head gasket blew, allowing coolant to pool on top of the piston. When you cranked the vehicle, the coolant created undue pressure and stress on the piston and rod. This would cause three possible scenarios, first the piston could have been damaged, second, the rod would have taken stress causing a break, bend or fracture. Third the pressure could have destroyed the tolerance of the rod bearing. Under normal repair of a blown head gasket, no mechanic could have diagnosed either without completely disassembling the engine and having all parts tested (very expensive). This is a circumstance that no one is at fault, and at this time still very costly. Trust me, I have two engines in the shop at this moment because of the same head gasket then bottom end failures.