In 1994 my Saab 900T needed a rebuilt head. Soon after, only a few hundred miles later, I went on a 1500-mile trip. Then, driving around in a Midwestern town on a very cold December day, I saw a lot of white smoke coming from the exhaust pipe, along with the sweet smell of antifreeze. I was very concerned about a coolant leak or a head gasket problem.
The auto parts salesman I talked to spoke of a product which I now believe was JB Stop Leak. It was made from ground-up flax seeds. I was skeptical, I did not think I wanted that stuff in my cooling system. But he swore that it was the best thing for my car.
It seemed to work. A few days later I went on another 1900-mile trip; I drove slowly to avoid stressing the cooling system, and I checked the coolant level every time I stopped for fuel. I just wanted to get to San Diego, where there was a great Saab mechanic that I knew from before.
I never lost a drop of coolant on that trip, and did not need to ask the mechanic to check out my cooling system. From the beginning of 1995 until I got rid of that Saab in 2004, I never had another problem with the cooling system. Whatever the problem was, JB Bars Leak solved it. It looked nasty, but it worked great.