What makes a loud knocking sound in the engine all of a sudden in idle? on 2003 Chevrolet Venture

I had a diagnostic run, and they said that my head gaskets are blown (but I have not oil leak nor water in the oil), cylinders 1,3,&5 are misfiring and the others are intermittent, the water pump was going bad, and there is a leak in the block (possibly just because the water pump is bad). Water pump did go, and I had it towed home. We replaced the water pump, and then started to flush the radiator and put stop leak in it. While running the car for about 5 minutes after putting in the flush solution, we revved the car just a little to help get the flush moving through the system and all of a sudden the engine started making a horrible loud knocking sound. We of course immediately shut it off, but now I am scared to turn it back on. Is the van done for?

by in Murfreesboro, TN on July 14, 2014
1 answer
ANSWER by on July 14, 2014
Oil level been checked?... How hot did the engine get when the H20 pump went out??.... Based on your discription, you need an engine!!