Diono first released their Monterey high back booster seat in 2008. It was immediately a hit with families and CPSTs because it provided an extendable back to accommodate their growing widths, and a tall back that allowed bigger kids to ride in a supportive high back booster seat. Some of our oldest CSFTL models started their booster seat journeys in a Monterey! Today, they are in high school or about to enter college.
Since the seat’s launch, Diono has updated the classic Monterey a couple of times. The newest version, the Monterey 4DXT, includes a remodeled headrest, enhanced fabric covering, contoured seat base and breathable exo-shell panels. This version of the seat is available in the United States and Canada. Even though we are in the midst of a global pandemic, we’re taking a look at this sleek new booster seat!
CSFTL Quick Stats
- Weight range: 40-120 pounds
- Height range: 38-63 inches
- Age: There is no age minimum listed in the Monterey 4DXT manual. CSFTL advocates that children be at least 5 years old before riding in a booster seat.
- Expiration: 8 years from date of purchase
- Requires vehicle headrest support to the tops of the child’s ears in both high back and backless modes
- Width at widest point of back when in narrowest setting: 21.5 inches
- Width at widest point of back when in widest setting: 24 inches
- Width at widest point of base when both cup holders stored: 18 inches
- Width at widest point of base when one cup holder extended: 20 inches
- Width at widest point of base when both cup holders extended: 22 inches
- Width at armrests: 19 inches
- Weight: 18.8 pounds in high back mode
- Weight: 6.9 pounds in backless mode
- Internal width at the child’s hips: 16 inches
- Internal width at the child’s knees: 17.5 inches
- Seat pan depth: 16 inches in backless mode
- Seat pan depth: 14 inches in highback mode
- Lowest shoulder belt guide: 16.5 inches
- Highest shoulder belt guide: 22.5 inches
The Monterey 4DXT features two extendable cup holders that can be used or stored underneath the seat. This already quite wide booster can be made even wider with one or both cup holders extended. While this makes the Monterey 4DXT less than ideal for 3-across scenarios, if there are only one or two children in the back seat, the extra cup holders may come in handy.
The Monterey 4DXT has a recline angle adjuster that can be adjusted to match the recline of the vehicle seat. The manual instructs caregivers to “push the back of the Monterey 4DXT backwards until you hear a click – the backrest will now move freely.”
We did this multiple times and did not hear that audible click, but there WAS a point where the backrest would move freely (and fall over). We assume this is the point where the recline is “engaged” (the booster is quite reclined once it reaches that point, though).
Position the Monterey 4DXT on the vehicle seat and slide the base back on the vehicle seat until it makes contact with the vehicle seat back. A gap behind the booster is acceptable as long as the head support is touching the vehicle seat back or head rest.
Seat Back Width Adjustment
The Diono Monterey has always been pretty unique in its ability to adjust the width as the child grows. The Monterey 4DXT is no exception, and the seat has the seat back width adjuster dial on the back of the seat. Make the seat back wider by rotating the adjuster clockwise or narrower by rotating counter-clockwise. There are no limitations about the settings in the manual, so we would recommend using the setting that is the most comfortable for the child.
The Monterey 4DXT features Diono’s classic, upside-down lower anchors. The manual indicates that, for ease of use, the lower anchors should be attached to the vehicle anchor points with the open end of the hooks facing up. If you’re familiar with using lower anchors to install a car seat, you will install the Monterey 4DXT by using the lower anchors the same way they are attached to the booster – upside down.
Simply attach the lower anchors to the vehicle anchors and remove the slack in the straps by pulling on both of the adjuster tails at the front of the booster seat. There is no need to test for movement or tighten the anchors until there is no movement since the lower anchors are simply provided to prevent the seat from being a projectile when unoccupied. If the lower anchors are not used, the child or their caregiver will need to remember to buckle the booster seat in when unoccupied.
Challenges and Specific Rules
I have been informed by other reviewers that the Monterey 4DXT manual storage location is pretty typical for Diono, but I will freely admit that I could not find it. I checked the box, checked out the seat, felt around, and was convinced my seat had shipped without a manual. I ended up downloading an online version of the manual in order to look up the storage location, and only then was I able to get my hands on the physical version of the manual that shipped with my seat.
In case you’re wondering, the manual stores in a pouch under the cover on the right side of the backless booster portion of the seat. The shoulder belt guide for backless booster mode is also in this pouch.
We wish that the manual shipped either visibly attached to the booster, loose in the box, or that the Monterey 4DXT featured SOMETHING on the cover to indicate that the manual is stored under the cover on the side of the booster. But alas, the manual storage location is well-hidden, and I fear that many caregivers will not be as thorough as I was with attempting to locate the manual, and will use the booster seat without reading it because they will be unable to find it.
Vehicle Headrest Support: Required
Because this is an important thing to note, we gave this its own section. While all backless booster seats require that the child have vehicle headrest support to the tops of their ears, the Monterey 4DXT also requires this support in high back booster mode.
Translation: if you’re intending to use the Monterey 4DXT in a seating position without headrest support, this may not be the best high back booster option. This stipulation is NOT mentioned in the manual, but Diono has confirmed this requirement of ALL their dedicated booster seats. We’d prefer to see this requirement be listed clearly in the manual.
To adjust the Monterey height, squeeze the head support adjuster and move the headrest up or down. The adjuster is quite smooth which makes adjusting the booster between children a quick and easy process.
The Monterey 4DXT ships unassembled, and requires assembly for high back booster mode. Here’s how to assemble the booster:
Attach the backrest to the seat base by inserting the backrest hook into the backrest opening at the rear of the seat base. Make sure that the seat base pad does not get caught between the moving parts.
- Rotate the backrest up until locked. When locked, the backrest will remain upright.
- Tuck the flap on the seat base pad under the backrest pad.
To remove the back and convert the Monterey 4DXT to a backless booster seat, perform those steps in reverse.
Fit to Child
High Back Booster Mode
Because we are writing this review amid a pandemic, our models are limited to only my children (and the child of another member of our team who also rides in a Monterey 4DXT), but we will try to be as thorough as possible in this section.
6 Year Old
Our 6 year old model is 50 inches tall and weighs 55 pounds. When asking children to pose for review photos amid a pandemic, you allow them to choose their wardrobe to keep the peace. The Monterey 4DXT almost seems to almost overwhelm her slender, lipsticked, angelic frame, but she fits nicely in the booster and claims it is very cushy. Our spring break was held just before the pandemic kicked into high gear, so we were able to take our models on a long (7 hour) drive as soon as this seat arrived. We’re very thankful that we had that opportunity, as long drives just aren’t happening nowadays.
This model found the Monterey 4DXT very comfortable, and even had a quick nap in the booster while we were driving. She has no complaints at all about the seat, and we liked that the seat belt fits her beautifully – centred on her shoulder and low on her thighs, touching her hips.
8 Year Old
Our 8 year old model is 54 inches tall and weighs 72 pounds. He typically wears a size 10 shirt. While he can legally ride without a booster seat, he is a couple of years away from passing the 5 Step Test, so he rides in a booster seat full time. We’ve found that the shoulder belt in our vehicles doesn’t fit him nicely in most backless boosters, and he likes the support of the back, so we were very happy that the Monterey 4DXT not only can accommodate his tall torso now, but it will continue to accommodate him for a while – possibly even until he is able to ride without a booster!
We have widened the Monterey 4DXT into the widest mode, and here we have adjusted the back to the tallest position to show how much room this model has to grow. At the highest position, the Monterey 4DXT belt guide is close to 4 inches above this model’s shoulder, which should give him at least a couple of years of growth!
8 Year Old
Our bonus model is 8 years old, 51 inches tall, and weighs 74 pounds. He also fits the Monterey 4DXT quite well and has lots of growing room (plus, look how beautiful the blue cover is!).
His mom noted that the back falls off easily when moving the Monterey 4DXT from one vehicle to another, but noted that he has plenty of leg support (he carries his height in his legs) and the natural recline of the booster is great for long car rides.
Fit to Child
Backless Booster Mode
6 Year Old
Our 6 year old model remains 50 inches tall and 55 pounds. She has never ridden in a backless booster before, and although the shoulder belt guide confused her initially, she was able to figure out to sit up tall and centered on the booster seat.
She needed the shoulder belt guide to help with her vehicle seat belt fit, but with it the belt fits her very nicely in this 2007 Honda Odyssey captain’s chair. The belt is centered on her shoulder and low on her thighs, touching her hips. It appears as if she might have difficulty maintaining her position without the back, as the booster is so wide, but since we have nowhere to go, we weren’t able to test out that theory right now.
8 Year Old
Our 8 year old model also maintains the same stats as above: 54 inches tall and 72 pounds. We’ve already determined that the Monterey 4DXT’s high back booster mode would likely last him until he is ready to ride without a booster, but we thought we would try the backless booster mode on him anyway.
In this 2007 Honda Odyssey’s 3rd row center seat, the shoulder belt comes out of the van’s ceiling. We found that the shoulder belt guide on the Monterey 4DXT was a necessary addition in this seating position because of the vehicle seat belt, and with it our model is demonstrating an excellent vehicle seat belt fit. Again, the vehicle seat belt is centred on his shoulders and low on his thighs, touching his hips.
Important Information: Where to Find
Like all booster seats, the Diono Monterey 4DXT requires a lap/shoulder belt to use, so therefore it is not FAA approved for use on aircraft. The backless portion is light enough that it could be a great travel option. Just carry it on board the aircraft, store it in the overhead bin, then use it in the car at your destination.
The Monterey 4DXT expires 8 years from the date of purchase. The label with the model number and date of manufacture is on the bottom of the seat. The expiration information is located in the manual.
Manual Storage — the manual storage is a bit hidden on the Monterey 4DXT. There is a manual storage pouch under the cover on the right side of the backless booster portion of the seat. The shoulder belt guide for backless booster mode is also stored here.
Date of Manufacture (and National Safety Mark for Canadian users) — located on the bottom of the backless portion of the seat.
Diono has produced many excellent booster seats over the years, and the Monterey 4DXT follows suit. While the width makes this a tough sell for most 3-across situations, and the requirement for vehicle headrest support limits the vehicles/seating positions the booster can be used in, for many children this booster seat would be an excellent, long-lasting, comfortable option.
The tall and wide back makes the Monterey 4DXT a great option for bigger children. Many children may be able to use this booster seat in high back mode until they are out of a booster completely – so having it convert to backless mode is a bonus but not necessarily a necessity. We found that it provided an excellent seat belt fit for both of our models in both high back and backless booster modes, and don’t doubt that it would fit children bigger and smaller than our models well.
Note: When carrying the booster in high back mode to the vehicle, support the bottom of the seat or you may end up with squished toes (ask me how I know). The backless portion of the seat falls off when the back is lifted, which is a bit of a pain (even though the back re-attaches quite easily).
Welcome to the market, Diono Monterey 4DXT! You’re going to make many children (and their caregivers) quite happy because of your tall and wide high back booster mode, and plush cover that comes in many different colors. Because why stop at comfortable when you can have comfortable AND fun?