Diono Radian 3RXT Car Seat

Narrow ChoiceDiono Radian 3RXT 3-in-1 convertible car seat in blue

  • What: Diono Radian 3RXT Car Seat
  • When: Birth to five years
  • Why: Multi-function, narrow, expensive
  • Where: Amazon

I loved the Diono Radian 3RX so much, I immediately ordered the upgraded version, the Diono 2019 Radian 3RXT All-in-One Convertible Car Seat, for my youngest child.

I wanted the extra headrest because unlike my daughter, who rides in the middle of the back seat, my son sits next to the door. I felt strongly about the additional side impact protection, and I hoped the headrest would expand beyond the seat shell so the seat would fit him longer.

Diono Radian 3RXT headrest and harness slots

The headrest does not extend beyond the seat and you have to uninstall the seat to change the harness height.

While the seat does offer an adjustable headrest, it does not extend past the edge of the seat itself. Unlike the Britax Grow With You and Graco Nautilus, or even the Evenflo Evolve, which offer a harness to booster option with adjustable headrest, the Diono caps out at the height of the seat back. 

I also had more trouble installing the 3RXT. I had zero issues with the less expensive RX version, and I looked forward to another simple installation. No such luck. It took me four tries to get a safe installation, where the seat didn’t move more than an inch at the belt path. Despite the fact I installed it in the same vehicle (a 2016 Subaru Outback), I tussled time and time again to get the seat belt tight enough. Since my child weighs over 50 lbs, we couldn’t use the LATCH anchors. I had no issue with that, as it worked out so well with the middle position. 

Diono Radian 3RXT seat cover stitched sewn shut

The Diono 3RXT seat cover includes a sewn stitch in the middle, making belt access in the forward-facing position tricky.

But the 3RXT has a cloth cover stitched together in the middle, making the belt access from the front much trickier. The RX has Velcro all along each side of the seat, with no permanently stitched areas to trip you up.

I also struggled to adjust the headrest. I was expecting the standard squeeze and pull handle. Instead, you have to undo both the seat cover and the headrest cover, then tug at an angle to get the headrest to move along the track in either direction. Even reading the directions multiple times, I still didn’t grasp it correctly. It took me several tries to discover I needed to remove the cover to allow the headrest to slide. 

Diono Radian 3RXT harness straps

You have to remove both the seat cover and the head rest cover to adjust the head rest height.

The harness can only be adjusted through the slots, meaning you have to uninstall the seat in the forward facing position to change the harness height. While that didn’t cause me any issues, as both my kids already sit at the highest harness height, it would irritate me endlessly if I had to struggle with the installation each time my child grew enough to need a harness adjustment.

Because this seat can be installed rear-facing, it doesn’t go as high as other booster seats. That means kids will outgrow it sooner (same as the 3RX) and need to move to a different booster. On the plus side, if you need a seat with a low profile to see safely out your rear window, this seat may make a difference. And I can’t complain about the narrow profile, either. These seats fit side by side in the same row, and I still managed to install two cup holders with the extra room. The narrow seat width makes a huge difference in tight spots.

Harness tightening strap on the Diono Radian 3RXT convertible car seat

The harness strap has to be pulled straight down to tighten, which works fine for the adult, but doesn’t let an older child easily operate it.

My son also has trouble tightening his harness when he buckles into the seat. The Radian 3RX doesn’t have the same issue, and my daughter can pull the strap with no problems. The 3RXT requires pulling straight down on the tightening strap, which can be a difficult angle for a kid buckled into the seat, even before achieving a tight harness. The buckle itself also seems to stick more on release than the 3RX model we have, though I’m hoping that eases with time and use.

This seat also folds flat, like many Diono models, making it easier to store and carry. It weighs quite a bit, though, and I wouldn’t recommend it for travel even with the fold flat feature.

Diono Radian 3RXT convertible car seat side view

The instruction manual tucks into the side of seat cover, making it tricky to access once installed (especially next to another car seat).

It has the same manual storage along the side of the seat, which I don’t like. I prefer a book I can access regardless of how a convertible seat gets installed (rear or forward facing), and much prefer Britax’s underneath the seat cover solution. 

While I thoroughly enjoyed the Radian 3RX, I won’t be recommending the 3RXT to anyone anytime soon. The headrest doesn’t provide additional room for growth, the seat can be tricky to install thanks to the stitched seat cover, and the harness buckle and tightening strap make it more challenging to use on a daily basis. If, like me, you only need a harness to booster option, you can find other brands which offer harnesses to fit taller kids. If you need a narrow seat, you may not have another solid option, in which case the downsides don’t ruin the seat, so much as make it less palatable.

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