2019 Diono Radian 3RXT Review: Diono Updates the Classic Folding Carseat

2019 Diono Radian 3RXT Review

Like its predecessor, the Radian RXT, the Diono 3RXT fills a niche for parents and caregivers looking for a narrow carseat that will grow with their child. The Radian line of seats has always been known for being 3-across friendly. Families with mid-sized vehicles and 3 kids are often well-served by Radians; I had one in my Civic for years when I had to fit a toddler and two teenagers in the back regularly. The current Radian series, the 3R3RX, 3RXT, and 3RXT JMC (Just My Color, a customizable fashion scheme) all share the Radian platform but extra features distinguish them from each other. We have a previous review of the recently discontinued RXT and the basic features and functions are very similar. This review will cover the basics and point out the updates to the new Diono 3RXT.

Radian 3RXT Weight and Height Limits

◦ Rear-facing: 5-45 lbs., height 44″ or less, and at least 1.5” of carseat above the child’s head*
◦ Forward-facing: 20-65 lbs., at least 1-year-old, height 57″ or less, child’s shoulders are not above top harness slots
◦ Highback booster: 50-120 lbs., 40-57” tall, and child’s shoulders must be at or above the 4th set of harness slots

*See Fit to Child section

some state laws have higher minimum age or weight requirements for riding forward-facing – find your state law here.

Radian 3RXT Overview

◦ 5 harness slot heights
◦ 12-position headrest
◦ 3 crotch/buckle strap positions
◦ Safe Stop Load Limiter
◦ Full steel reinforced frame and aluminum reinforced sides
◦ Folds flat for travel and storage
◦ Lined with EPS foam
◦ Rear-facing tether capability
◦ Deluxe push-on latch connectors
◦ One of the narrowest convertibles on the market: makes 3-across much easier
◦ Low profile makes loading and unloading child easier

3RXT Updates:

◦ 65 lb. weight limit for the harness (this is more realistic than the previous 90 lb. weight limit)
◦ Full wrap cover makes for neat and tidy storage of unused straps and accessories on the back of the seat


3RXT Measurements:

Harness height: 9”, 10.5”, 12”, 15”, 17.5”
Crotch strap depth: 3.5”, 5.5”, 7”
External widest point: approx. 17” at widest point at shoulders, 16.5” at widest point at thighs
Internal widest point: approx. 14” at widest point at shoulders, 14.5” at widest point at thighs
Seat weight: 27 lbs.

2019 3RXT Fashions:

Black, Dark Grey, Red, Plum, Yellow Sulpher, Grey Oyster, Blue


Under the Cover:

There are no easily noticeable changes to the basic shell of the seat. It features the same EPS foam, the same folding mechanism, and the same steel reinforcements. There are some minor differences which are not easy to photograph clearly. The shoulder belt guide for booster mode has been redesigned so it’s more likely to promote proper retraction of the seat belt – something the manual helpfully points out should be checked for with each installation (this is good advice for all highback boosters). Some of the EPS foam is black instead of white. Other than that, the 3RXT is nearly indistinguishable from the RXT once its cover has been removed.

Full Wrap Cover:

After using this seat for a while, I realized that this is a bigger innovation than I initially thought. The first thing I noticed about the new full-wrap cover was the aesthetics. I spent several years staring at the back of a rather unsightly Diono car seat in my Civic. Other car seats on the market aren’t any better to look at from the back. Now that more and more state laws are moving to “rear-face until two” laws and more families are understanding the benefits of rear-facing even longer than that, it’s about time the back of the car seat got some cosmetic attention. Now instead of looking at a bunch of adjustment mechanisms, harness splitters, stored top tethers, and other sundry pieces of equipment, we can actually look at the sleek and soft fabric in a color of our choosing. My youngest child is four and our rear-facing days are numbered, but I’m going to be totally honest – if I were starting over today this would be a factor in my decision. Car seats are like furniture in our cars and we see them every day for years. It’s worth looking at a car seat that makes you feel happy and well put together.

The more I think about this new cover design, the more I like it for practical reasons too. There are fewer opportunities to catch or snag straps or accessories on the back of the seat when moving it around. I would no longer worry about something getting caught in the x-ray machine at the airport as I send the car seat through (something I’ve done a couple of times with a folded Radian and always worried about). It keeps curious children from being attracted by all those loose dangly things on the back and removing, losing, or just messing with them.

Mad props to Diono for giving some extra thought to the back side of a convertible car seat. It’s about time someone redesigned that mess.

Back of the 3RXT. The top zips down to expose the LATCH hardware, Safe Stop, and Locking Clip. The bottom zips up to provide access to the manual pocket (note the manual icon) and the back of the harness.


Rear-facing Installation

Installation of the Radian 3RXT in the rear-facing position is the same as previous Radian models. It is either easy or difficult; there doesn’t seem to be a middle ground with this carseat. In order to install the Radian rear-facing, you must first attach the rear-facing base/boot. That base/boot will determine the recline angle in your vehicle and the angle will vary depending on the slope of your vehicle seat. You will not need any rolled towels or noodles to achieve a proper angle. In fact, Diono does not allow the use of rolled towels or noodles with Radians.

For an older child who has good head control and can sit upright unassisted, the Angle Adjuster accessory can be used under a rear-facing Radian to make it more upright and give front seat passengers inches more legroom too.

Rear-facing with the Huggable Images toddler in a 2015 Expedition. Fully reclined without angle adjuster.

Diono 3RXT with Huggable Images Toddler, rear-facing with Angle Adjuster in a 2015 Expedition.

The angle adjuster leaves lots of room for the front seat passengers to adjust their seats comfortably.

The RF belt path is a closed belt path, meaning it’s enclosed in plastic. If you’ve got big hands, you’ll have trouble fitting the seat belt or SuperLATCH belt through the belt path; it can even be challenging for average sized hands, although with practice it gets easier. Because it’s closed, tightening the belt for a tight installation can be difficult too, especially if the female end of the seat belt buckle is close to the belt path. The best way to get a carseat tight is to pull the belt in the same direction as the belt path, but with a closed belt path, this can be challenging. Be patient and be prepared to tighten, rest, and tighten again in some vehicles.

I have a seat belt system in my vehicle that is pretty much ideal for installing a Radian. The female end of the buckle is very close to the vehicle seat bight (crack), leaving plenty of room to get leverage for tightening the seat. I have used previous models of the Radian (same design in this regard) with other types of seat belt systems which are not as easy.

In my vehicle, and in my experience with previous models in a variety of vehicles, installing the angle adjuster also made it easier to get a tight fit with the seat belt.

Forward-facing Installation
Installing the Radian forward-facing can be easier than rear-facing because the cover can be pulled away for access to the FF belt path. Vehicle buckles that are on short buckle stalks or ones like mine that are even with the vehicle seat can pose an extra challenge because the seat belt will bunch in the latchplate the tighter you pull. This is normal for this car seat, and in fact isn’t unusual for car seats in general. What I did to get it tight was tighten the best I could, unbuckle, carefully straighten the seat belt in the buckle so I could take a little more slack out, then kneel into the car seat and re-buckle. It wasn’t very difficult, but for a car seat novice it won’t be an obvious “trick” and it could be a source of frustration.

In my vehicle, I got an excellent and fairly easy installation forward-facing in the center where I don’t have a forward-leaning vehicle head restraint.

Behind the driver, however, the middle back of the car seat is not in contact with the vehicle seat at all. The top of the restraint rests on the non-removable forward-leaning head restraint in the car. This made getting a tight installation much more challenging, although I was able to accomplish it after several tries. I contacted Diono about this (with photos) and was informed that as long as the install was secure, it was not necessary to have the back of the child seat flush with the vehicle seat. So while more difficult, this did not create an incompatible situation.

Special forward-facing concerns:
Adjustable Bottom: When installing the Radian forward-facing, the 3R, 3RX, and 3RXT models require that the forward-facing adjustable bottom be lowered for children between 20 and 25 lbs. Most forward-facing children will be over 25 lbs., or will be soon, so that means you should simply plan on lowering it before installing the Radian FF.

Squeeze these two bars to lower the bottom of the 3RXT into the recline position, required for most forward-facing installations.

The forward-facing recline lowered as is necessary for all forward-facing children weighing more than 25 lbs.

Safe Stop Load Limiter: This small strap that is attached to the back left of the carseat when you first receive your Radian is called a load limiter. Its purpose is to increase the amount of time over which your child feels crash forces. If you install the Radian FF for a child who weighs under 40 lbs., you must use the Safe Stop. The Safe Stop is never used rear-facing.

When setting this seat up in forward-facing mode for my 36 lb. model, it was important to install the Safe Stop load limiter – required for all forward-facing children under 40 lb. It needs to be removed when the child reaches 40 lbs.

Lap-Only Belt Installation without Top Tether:

If your vehicle has a lap-only belt without a top tether anchor and you need to install the 3RXT in that position, there’s a Lap Belt Cushion that is required to be used in the seat. It significantly reduces the length of the crotch strap, though Diono offers a longer strap if you call and request one, and reduces the height of the harness slots because it’s a piece of 1″ thick EPP foam with memory foam on top. We recommend that you try to find another seating position in the vehicle if you can. The Lap Belt Cushion is not required for use on an airplane where the only type of installation is a lap-only belt.

Booster Installation

When the carseat is used as a booster, it may be LATCHed in at any weight. This is because the LATCH is simply holding the carseat to the vehicle while the seatbelt is restraining the child and will be the device taking crash forces. I could not find instructions for using LATCH in booster mode in the manual, but our contact at Diono assured me that this is still allowed as it has been in previous models. Both the lower anchors and the top tether may be used in booster mode.

The manual helpfully reminds the user to check to ensure the vehicle belt retracts properly in booster mode. This has been an issue with previous RXT models, and to be fair it can be an issue with almost any highback booster as it’s impossible to check compatibility of every booster at every height adjustment level in every vehicle on the market. It can be a serious problem when the shoulder belt gets caught in the belt guide because if a child leans forward and the shoulder belt doesn’t retract automatically, it stays loose and floppy on the child and could lead to the child being severely injured in a crash. The belt fit and geometry is otherwise very good and even earns it an IIHS Best Bet rating as a booster, but the IIHS doesn’t measure booster fit with real, moving kids.

I tried the RXT in two very different seating positions in my car. On the driver’s side, the seat belt is mounted to the frame of the vehicle. In the center, it’s seat-mounted to the right of the car seat. In both positions with my 6 year old Huggable Images doll, the seat belt extended and retracted properly. Here’s a video demonstrating the proper seat belt retraction.

Installation Methods

The SuperLATCH connectors are the deluxe IMMI push-on style connectors, similar to the push-on connectors on other seats. There is an adjuster on one side of this strap. There are storage areas at the top of the shell to store the LATCH and top tether connectors when not in use, which can be accessed by zipping open the top of the cover in back. The tether strap can be used rear- or forward-facing. While tethering a forward-facing child restraint with a harness is always recommended, a top tether is not required for this seat if one is not available. Unlike previous versions of the Radian, the manual indicates the tether is required for the 3RXT if one is available.

LATCH Weight Limits:

Rear-facing LATCH weight limit: 35 lbs.
Forward-facing LATCH weight limit: 40 lbs.

Center LATCH installations with Non-Standard Spacing:
Diono allows LATCH installation in the center seating position if the vehicle manufacturer allows it and the LATCH anchor bars are spaced 11-14” apart.

Inflatable Seat Belts
Diono has determined that the Radian carseats can be installed with inflatable seat belts found in Ford Motor Vehicles. This does not include Mercedes vehicles, inflatable seat belts found on aircraft, or any other inflatable seat belts.

Fit to Child

The Radian 3RXT comes with an infant head pillow insert and a body support insert. These items are optional and you can remove either of them at any time.

Huggable Images newborn doll with body and head inserts provide an acceptable fit for this doll.

Newborn doll with body insert but without head support insert. This provides an acceptable fit for this doll, but would not for a smaller newborn.

The Radian also comes with a set of memory foam harness pads. For the last several years, these have been required for forward-facing, and optional for rear-facing. I was not able to find guidance for this in the manual, but when I contacted Diono I was informed this has not changed – always use the harness covers for forward-facing children.

Because of the well-padded cover and memory foam in the seating area, the Radian is a comfortable carseat. It won’t fit small newborns well, even with the body support, because the bottom harness slots are too high. A larger newborn may or may not fit well. Our Huggable Images newborn model has an acceptable fit.


The manual has an error in it that is probably overlooked, but is significant nonetheless. In listing the rear-facing fit requirements in several locations, it states, “Top of head must be 1.5 in. below the headrest ears.” Following this fit requirement strictly means that the 3RXT would be outgrown before toddlerhood. It is a misprint and the manual should read, “Top of head must be 1.5″ below the top of the headrest.”

The rear-facing capacity of this seat has not been the highest on the market in several years, but it’s still respectable and will comfortably fit most children in a rear-facing position until about age four. My petite four year old, weighing in at 36 lbs. and standing 39″ tall, still has plenty of room to grow before she would need to switch to forward-facing in this seat. My 100th percentile older child outgrew her RXT RF at age 3 years 7 months, and in terms of capacity I’d expect the exact same from the 3RXT. This is plenty of rear-facing capacity for the vast majority of children out there.

Rear-facing mode with a 4 year old, 39″ 36 lb. child. She likes the seat and the low sides make it easy for her to sit criss-cross.

3rd Harness Slots

When the child is using either of the bottom 2 harness slots, the headrest must be moved out of the way, positioned in the top-most spot. Once the child is using the 3rd slots, it can be moved down. My Huggable Images toddler doll’s shoulders were even with the 3rd slots. This doll is supposed to represent an average 16 month old child.

This 16 month old Huggable Images doll is just barely tall enough to use the 3rd harness slots, and therefore the head wings.


For forward-facing, average sized kids should make it easily to belt-positioning booster seat age in the harness. My daughter’s shoulders are barely above the 3rd set of harness slots; she has plenty of space to go before needing the 5th set of slots which are about 17″ high.

Our 4 year old 39″ 36 lb. model is delighted to show off the 3RXT in forward-facing mode.

This shorter than average 39″ tall four year old would use the 4th of 5 sets of harness slots if she were forward-facing in this seat. She should have no trouble reaching a mature booster age before outgrowing the 3RXT.

Booster Mode

In booster mode, we have more mixed results. The stated size range for children using this seat as a booster is 50-120 lbs and under 57 inches tall, which Diono estimates to be around age 10. My 6 year old Huggable Images doll represents a 48” tall 46 lb. child. She fits well but does not have a lot of growing room left in this booster at that size. On the other hand, the seat belt does seem to be positioned well on the model, so if you do happen to have a child over 50 lbs. who is short enough to fit comfortably, it should make a safe and appropriate booster seat. Children who are shorter and stockier, and children who have longer legs and shorter torsos, are more likely to be able to use this seat as a booster than children who are long and lean or who are taller in the torso than in the legs.

Our 48″ tall Huggable Images doll fits comfortably in the 3RXT in booster mode.

Many children, however, especially ones that are somewhat lightweight for their height, will be too tall to physically fit into the seat by the time they reach the minimum booster weight of 50 lbs. I had my 8 year old child sit in the seat. She is tall for her age, at just under 56 inches, and weighs 76 lbs. I would say she is of average build. According to the stats in the manual, this seat should fit her as a booster. The shoulder belt guide is approximately 3” below her shoulder, and she is physically unable to actually sit in the 3RXT because her shoulders do not fit between the headwings. It is hard for me to imagine any child approaching the stated upper height limits of the seat, even one with a shorter torso and longer legs, fitting into this seat safely. In fairness to Diono, this issue of being overly optimistic on the box with what size child will actually fit in the car seat is common industry-wide.

Boosters in general are like clothing – different ones provide better or worse fit on differently shaped children. Because of this reality I would not usually count on any all-in-one seat to last a child from birth to booster; it’s just too hard to predict a child’s stature at age six before the child is even born. If you find this seat (or any all-in-one seat) still works for you during the booster stage, consider that a bonus.

This 76 lb. 56″ tall child cannot physically squeeze into the 3RXT to test it out as a booster.

Cover/Maintenance/Ease of Use

The cover is well-padded with a comfortable texture. Diono recommends machine washing in cold water with gentle detergent on the gentle cycle and laying flat to dry.

Do not wash the memory foam!

From the beginning, the Diono Radian car seats have had a ratcheting harness adjuster which tightened with a tug-tug-tug motion. The 3RXT still has this feature, but I felt it was a lot smoother and easier to tighten than previous Radians I have owned. The adjuster mechanism looks different from the RXT, so perhaps this is part of the whole re-design. The harness height still adjusts from the back of the seat. The rear cover must be unzipped to access the harness slots, and each strap is removed from the metal splitter plate and re-threaded through the correct harness slot. Use the slots at or below the shoulders for rear-facing, above for forward-facing. Also, the top of the child’s head must be 1.5” below the top of the car seat for rear-facing, and the tops of their ears must be below the top of the car seat for forward-facing.

FAA-Approval/Lifespan/Crash Guidelines

The 3RXT is FAA-approved for use in aircraft when used as a harnessed seat. It also is a heavy restraint weighing in at 26.5 lbs., so if you do travel with it, you’ll want to use a luggage cart to avoid having to carry it. It does not come with a carry strap like the older RXTs used to, although Diono assures me the ones they sell on their website as an optional accessory will work. Since the Radian seats are some of the narrowest on the market, you won’t have any problems fitting one in a plane seat AND the tray table will be able to come all the way down for a forward-facer. For rear-facing, the Angle Adjuster may make the seat fit depending on the pitch of the seats on the plane your flying. Buying a snack for the person in front of the carseat certainly doesn’t hurt ;). Remember that it can only be used with the harness on the plane since belt-positioning booster seats can’t be used on planes. The lap belt cushion which needs to be used in the car for a lap belt installation without a top tether does NOT need to be used on an aircraft.

There are 2 FAA-approval labels: 1 on the back of the seat near the LATCH and tether connectors storage location and 1 on the right side of the cover.


The 3RXT expires 10 years from the date of manufacture.

Diono recommends replacement after any crash.


◦ 3 Crotch Strap Positions: Having a choice of crotch strap positions makes the harness more comfortable for bigger kids.
◦ Low and narrow footprint means it’s more likely to fit in tight spots.
◦ Padded Cover: A thickly padded cover, plus the memory foam in the bum area, makes for a comfy seat.
◦ Folds flat for travel and storage.
◦ Enclosed fabric back improves aesthetics when rear-facing in the car, and convenience for storage and travel.
◦ Low profile makes loading and unloading child easier.
◦ Can be installed with Ford Motor Company inflatable seat belts.


(In all fairness, these aren’t necessarily problems but I list them here to inform potential consumers of specific Radian 3RXT issues)
◦ Low LATCH weight limits.
◦ Head wings are a serious pain to adjust up and down.
◦ Installation: Often more difficult depending on the vehicle, with a higher learning curve due to the various features.
◦ Booster mode will be useless for the majority of children, and of limited usefulness for the rest of them – does not live up to its marketing claim of being the only seat you will need up to 57” or 120 lbs..
◦ Heavy for a carseat designed for travel.
◦ The padding on the crotch strap fell onto the floor literally every time I unbuckled a child or a doll from the car seat. Diono says the padding is highly encouraged for comfort and to protect against hot buckles in the sun, but it is not absolutely required; which is good because I predict it will be left behind in a parking lot somewhere in short order.
◦ The manual leaves a lot of unanswered questions which led me to contact the company for clarification. I can see this being an issue for a lot of parents who would sooner guess at the proper use than call the manufacturer if they can’t find the information in the manual.


The Diono Radian 3RXT is a solid convertible seat with great rear-facing features. Its high height and weight limits accommodate big kids both rear- and forward-facing, yet it takes up less space than many of its competitors. For narrow backseats or 3-across situations, you simply can’t beat the width of the 3RXT. Features like rear-facing tethering, thick padding, and solid construction make the Radian 3RXT a smart purchase. Don’t expect it to be the last car seat your child will use, as few children will ever fit properly in booster mode and those who do will certainly outgrow it before they are big enough for a seat belt alone.

Thank you to Diono for supplying the 3RXT used in this review! No other compensation was provided. All opinions expressed are those of CarseatBlog.


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