I have a '11 F250 and the check coolant additive light came on. I bought this truck used with 108K, it now has 120K. I took it to my dealership and they performed a test, but only used 1 test strip. It checked ok, but I'm not confident that evrything was checked correctly. I asked the tech about the 3-strip test and he said the one test strip is all they ever use. I'm not sure when, if ever, the coolant has been changed or additives added, etc.. Any suggestions, I'm thinking that getting the 3-strip test and do it myself would be the way to go....?????