We had to drive about 120 miles after the gasket blew out. I put 1 bottle in before we left. We had to stop frequently to let the water cool down and add a gallon or two. About 90 miles into the trip, we were having to stop every 5 miles or so to cool off. I put in a second bottle and drove the last 30 miles without stopping. The block seal didn't do any extra damage, in fact we probably wouldn't have gotten home without it. I have heard of other Hummer owners that used this product at an earlier stage of failure and drove for months afterward before making repairs.
Scot Smith
1994 HMC4, Locked
"They're right, Wider IS Better..."
Southern Axle & SteeringRemanufactured Driveline & Steering Parts for Hummers