Diono Radian 3RX Car Seat Update

Diono Radian 3RX convertible car seat installed forward facing in third row of Mazda5

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What Works and What Doesn’t

Diono Radian 3RX convertible car seat installed forward facing in third row of Mazda5

  • What: Diono Radian 3RX Car Seat Update
  • When: Birth to 120 pounds
  • Why: Narrow, fits three across
  • Where: Amazon

I bought a Diono Radian 3RX convertible car seat for my daughter almost a year ago, when she outgrew her Britax Marathon convertible seat. At just over 40 lbs, and 44 inches tall, I wanted to keep her in a five point harness as long as possible, so I wasn’t quite ready to make the switch to a belt positioning booster. As an added requirement, the seat had to fit three across in the row with her brother’s Graco Nautilus Elite 80 and another forward facing Britax Marathon for her younger brother in the backseat of our 2016 Subaru Outback. That didn’t leave a lot of room, or choices.

Diono Radian 3RX between Graco Nautilus 80 elite and Britax Boulevard in back seat of Subaru Outback
The Diono Radian 3RX fit into the snug middle spot between two other forward facing seats in our 2016 Subaru Outback.

The Diono Radian 3RX can go from a rear facing infant car seat all the way to a belt positioning booster up to 120 pounds. Yet it still folds flat for easier storage and to make it more travel friendly. It has five slots for the harness, and one path for the seat belt once kids make the transition. The harness can go up to 65 pounds, which sounded promising. Even better, it lasts for up to 10 years, instead of expiring in 6 to 7 years like most car seats. 

The Diono Radian 3RX went into that middle spot so nicely, I bought a second one when her younger brother outgrew his Marathon. Both seats installed easily in the Subaru Outback thanks in part to the reclining seat back and removable headrests, which helped get the correct angle. They also had no trouble with the different seat bottoms in the middle position and behind the driver’s seat. As an added bonus, the low profile made it easier to see out the rear window as well.

Diono Radian 3RX next to Graco Nautilus Elite 80 in third row of Mazda5
The Diono Radian 3RX blocks a lot less of the read window of our Mazda5 when installed in the third row and compared to the Graco Nautilus Elite.

Like most seats we’ve tried, my kids outgrew the limits in height well before they got anywhere close to the maximum weight limit. Then over the summer, we traded in our Subaru Outback for the three rows (and increased towing capacity) of a 2015 Audi Q7. After the ease of installation with the Diono Radian 3RX in our station wagon, I almost looked forward to moving the car seats over to another vehicle. Much to my dismay, the Audi headrests can’t be removed. And getting a secure installation in the second row proved almost impossible. Even given the narrow width of the Diono, it overhung the slimmer middle seating position in the second row. That isn’t allowed with the Diono car seat, so I moved it to the outboard position. There, the dip in the seat bottom coupled with the non removable headrest meant I had to roll up a towel to have a chance at a proper installation. Even then, I relied on installing the car seat with the bench seat forward, then pushed the bench seat back to remove the extra slack in the seat belt. (I never tried the LATCH installation because my child weighed more than 40 pounds, which exceeded the limit for that type of installation.) It took me hours of fighting to get the installation right, and I still had to do it all over again with the same seat for my son.

Diono Radian 3RX five harness slots
The Diono Radiam 3RX has five harness slots, but you have uninstall the seat to rethread the harness when you need to adjust it. It does not have an adjustable headrest.

Fast forward six more months, and my daughter has transitioned from the harness to the seat belt in our other car, where she rides in a Britax Grow With You. Since the Britax can’t overhang the bottom of the bench seat in booster mode (though it can in harness mode), we switched it with the Diono to avoid buying yet another belt positioning booster. I installed the Diono in the third row of our 2012 Mazda Mazda5, and had similar issues. The Mazda doesn’t have LATCH anchors in the third row, so I had to use the seat belt option. Yet the long stem on the seat belt receiver, coupled with the angle of the seat bench and the non-reclining seat back, made it almost impossible to get a safe installation. No matter how much slack I removed from the seat belt, the entire seat still moved more than four inches after tightening. Multiply those inches by the force of a car crash and I didn’t feel comfortable using the seat.

After more than an hour, I got a decent installation, though it still isn’t up to my usual standards. If you need a narrow seat for a three across situation, the Diono Radian 3RX may be one of your few choices. And it’s certainly cheaper than buying a new car. The lower profile of the seat (this model doesn’t include an adjustable headrest) also works great for anyone who needs visibility out the rear of the vehicle. But the difficulty in installing the seat in two completely different automobiles in several different seating positions, along with the need to rethread the five point harness anytime your child grows, means you sacrifice a lot of time and potentially safety getting this seat installed repeatedly as your child grows.

If I had it to do over again, I’m not sure what I would do differently, since we needed the narrow seat for a three across installation. But I wish I had had more options to keep my kids in a five point harness longer.

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