Copied from other thread, but...
Oh good lord NO! Never, ever put any of those radiator leak seal products in any car with a modern cooling system (post 1980s). They usually contain either a silicate or poly additive that will clog your radiator passages no matter what the marketing hype says. Modern radiators have very small coolant passages and will clog with that stuff. Plus if you have a significant leak, that won't do squat anyway. Better off fixing the actual problem than adding something that could lead to a more costly repair.
I would MAYBE use it if I was 100 miles away from civilization, had no extra water or coolant to add, and HAD to for an emergency... with the full knowledge that I would later have to fix the original problem, flush the entire system about half a dozen times to get all that gunk out, and refill with fresh coolant and then keep a sharp eye on my temp guage for any residual issues that may crop up over the next 10K miles.
Put it this way. If you took your truck to a mechanic for the leak and he gave it back to you 15 mins later and said "All done, I poured some of this magical fairy juice in your radiator and it's all better now. Have a great day!", would you trust him that the repair was done properly?