How long can I use the radian 3R, 3RX, or 3RXT in booster mode? June 07, 2021 11:02 Updated The Radian 3R series can be used up to 120 lbs. while in booster mode. If you’d like to find out more about the Diono Radian 3RXT visit our store: https://store.diono.ca/radian-3rxt/ Related articles How long can I use the radian 3R, 3RX, or 3RXT for harnessed forward facing? How long will it take to receive my Diono order? Radian 3RXT Comments 0 comments Article is closed for comments.