Two Days Under the Gladiator: Plugs, Oil Cooler, Shocks, Springs, Oil Change, and Tire Rotation

(Preface: I didn’t intend to blog about this maintenance marathon before hand. Therefore I didn’t get the all of the photo coverage I now wish I would have.)

There are weekends where you go wheeling.

There are weekends where you clean the truck, check the fluids, and tell yourself you’re going to get around to that maintenance list soon.

And then there are weekends where you look at your high-mileage Jeep Gladiator and say, “Alright. It’s time.”

Memorial Day 2026 was one of those weekends.

My 2021 Jeep Gladiator Mojave has crossed well into the 100,000-mile club, and while it still runs strong, the maintenance list had started getting loud enough that I couldn’t ignore it anymore. Spark plugs were due. The factory plastic oil cooler/filter housing was living on borrowed time. The suspension was tired. The shocks had already sent me down a research rabbit hole. The oil needed changing. Tires needed rotating.

So I carved out two days, cleared the schedule as much as possible, and turned the driveway into a Gladiator maintenance bay.

This was not a random Saturday morning impulse, either. I had placed the orders for all the major parts weeks before. The Dorman all-aluminum oil cooler kit came from Amazon. The NGK spark plugs came from Amazon. The Falcon SP2 2.1 Monotube JT shock kit came from Northridge4x4, along with the Mojave-specific bushing adapter kit.

In other words, this maintenance marathon had been quietly building in the background for a while.

By the end of it, the truck had:

• New NGK spark plugs
• New Dorman all-aluminum oil cooler/filter housing
• New Falcon SP2 2.1 shocks
• New springs (slightly used take-offs purchase on EBAY)
• Fresh oil and filter
• A tire rotation

And one tired owner with sore hands, a little more experience, and a much better-sorted Gladiator.

Day One: Spark Plugs and the Oil Cooler Rabbit Hole

The first job on the list was spark plugs.

On the 3.6L Pentastar, spark plugs are not the worst job in the world, but they are also not exactly a quick 30-minute maintenance item. The intake has to come off, access gets tight in places, and once you’re that far into the engine, the temptation to handle other known failure points becomes very real.

That’s exactly what happened here.

I started with the plugs. I used NGK plugs and decided to reuse the factory coil boots because they were still in great shape. No cracking, no obvious wear, no reason to throw away good factory parts just to say everything was new.

But once the intake was off and the valley of the engine was exposed, I decided this was the right time to deal with one of the more infamous Pentastar weak spots: the factory oil cooler/filter housing.

From the factory, the oil cooler unit is plastic. And while plenty of them last a long time, they also have a reputation for becoming a leak-prone failure point as these engines age. On a higher-mileage Gladiator, especially one I depend on for daily driving, road trips, camping, and trail use, this felt like the right “while I’m in there” move.

So I replaced the factory plastic unit with the Dorman all-aluminum oil cooler/filter housing.

That one decision turned the spark plug job into a much bigger service day, but it made sense. The intake was already off. The labor overlap was already happening. And frankly, I’d rather replace a known weak part in my driveway on my own schedule than have it fail later on the side of the road or in the middle of a trip.

A major shout-out here goes to Gator Overland for the extremely thorough spark plug and oil cooling unit video. That kind of detailed DIY content is exactly what makes a job like this less intimidating. It still takes time. It still requires patience. But having someone walk through the process clearly before you start makes a huge difference.

I took my time. I cleaned as I went. I checked connections. I didn’t rush the gasket surfaces. I made sure everything was seated properly.

All in, the spark plug and oil cooler job took me about eight hours, including a couple of breaks.

Could it be done faster? Sure.

Would I rather take my time on a job that involves the intake, oil system, coolant connections, sensors, and a known leak-prone assembly?

Absolutely.

The “While I’m Here” Oil Change

Once the oil cooler was replaced, it made sense (and is really required) to go ahead and do the oil change as part of the same job.

Anytime you’re replacing the oil cooler/filter housing, you’re already opening up part of the oil system. There’s no reason to button everything back up and leave old oil possibly mixed with water in the conversation.

So the Gladiator got fresh oil and a new filter as part of the Day One service.

This is one of those maintenance moments that feels bigger than the parts list. Spark plugs are basic. Oil changes are basic. But when you combine plugs, an oil cooler replacement, and fresh oil, it feels like you’re giving the engine a real reset.

At 100,000+ miles, that matters.

This truck has earned its keep. It has been driven, loaded, camped out of, road-tripped, commuted in, and used. But keeping a high-mileage Jeep healthy is not about waiting for things to fail. It’s about staying ahead of the predictable stuff.

And the Pentastar oil cooler is predictable enough that I decided not to gamble with it.

Day Two: Springs, Shocks, and the Suspension Saga

The next phase was suspension.

Or more accurately, the next phase was finishing a suspension job I had already tried to start the weekend before.

That first attempt did not go as planned.

I had originally ordered a set of Bilstein shocks that Amazon said would fit 2021 Jeep Gladiator Mojave. On paper, that seemed like a reasonable option. Bilstein has a strong reputation, the 5100 series is popular across trucks and Jeeps, and the Amazon fitment checker gave me the green light.

The problem?

They do not fit the Mojave.

Once I got into the job and realized the Bilsteins were not going to work, I stopped. I was not going to force parts onto the truck, modify something that should not need modifying, or pretend a “close enough” suspension install was good enough.

It wasn’t.

So I backed out of the job, buttoned things up, and went back to researching. (Note I also contacted Bilstein support directly and they confirmed “Bilstein does not offer shocks that work with the front upper shock mounts with the Gladiator Mojave trim package. Bilstein doesn’t have any remondations on modifying the upper shock mounts in the front to accept our shocks.”)

That was frustrating for several reasons.

First, the Amazon listing information was wrong for my application. It said the shocks would fit a Jeep Gladiator Mojave, but that was not the case. (They have since revised this.)

Second, the seller was not an authorized Bilstein dealer. The return was approved, but I had to pay the return shipping myself, which ended up costing almost $60.

So the Bilstein detour cost me time, momentum, and money.

That is the part of DIY maintenance nobody puts in the glossy build posts. Sometimes the wrong part shows up. Sometimes the fitment chart is wrong. Sometimes the seller is technically allowed to sell the part but is not an authorized dealer. Sometimes you pay a $60 tuition fee just to learn that “Amazon says it fits” does not always mean it actually fits.

And in this case, the lesson was clear: The Mojave is its own animal.

The factory Fox shocks, hydraulic jounce bumpers, ride height, shock mounting details, and Mojave-specific suspension setup all matter. Mojave fitment is not always the same conversation as a Sport, Overland, Willys, Rubicon, or standard non-Mojave JT.

After that false start, I did more research and changed direction.

I had also looked into rebuilding or exchanging the factory Fox shocks. That led me to All-Terrain Shock Solutions out of Houston, Texas. Their rebuild and exchange programs seem like a great option, especially for someone who wants to keep the Mojave close to its original factory design.

But for me, it still didn’t quite make sense.

The factory Fox Mojave shocks are impressive, but they are also more shock than I really need for how I actually use this truck. I’m not bombing desert whoops. I’m not racing. I’m not pushing the Mojave the way that original Fox setup was designed to be pushed. Most of my miles are highway miles, work miles, road trip miles, and weekend adventure miles.

I wanted a suspension refresh that made sense for my real-world use.

In the end, I pivoted to the TeraFlex Falcon SP2 2.1 Monotube JT shock kit from Northridge4x4, along with the Mojave-specific bushing adapter kit.

That felt like the right balance: quality, simplicity, Mojave-aware fitment, and a more practical match for my actual driving style.

A Footnote on Using AI for Parts Research

I should also make one honest note here.

I used AI as part of my research process when looking into the Bilstein option, and it never flagged that those shocks might not fit my Mojave.

That’s on me.

AI can be incredibly helpful for comparing options, explaining procedures, summarizing forum discussions, and helping you think through a project. But it should not be treated as the final authority on parts fitment, torque specs, safety procedures, warranty questions, or vehicle-specific compatibility.

Use AI as a research assistant.

Do not use it as the final word.

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REMEMBER: Before committing to parts for your Jeep, especially suspension, steering, braking, driveline, or engine components, verify fitment directly through the original manufacturer, an authorized dealer, or support chat. Cross-check the actual part numbers. Confirm the trim package. Confirm Mojave-specific details. And when in doubt, ask a human who sells, installs, or manufactures the part.

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That one extra step could save you a weekend, a return shipping fee, and a whole lot of frustration.

The Bushing Adapter Kit and the Bench Vise Upgrade

One thing worth noting: the Falcon shock install was not simply a matter of opening the box and bolting everything on.

Because this is a Mojave, the front shock bushings required attention. The Falcon kit uses a Mojave-specific bushing adapter kit, and that means the factory bushings have to be pressed out and replaced with the correct Mojave bushings.

Those bushings are bigger and beefier.

And they are not something you casually pop out with a screwdriver and optimism.

This part of the project required me to upgrade my bench vise from a 4-inch vise to a 6-inch vise. The smaller vise simply was not up to the job. To press out the factory bushings and install the Mojave-specific replacements properly, I needed more size, more leverage, and more stability.

So, in classic DIY fashion, replacing shocks also meant upgrading a tool.

That’s not necessarily a bad thing. A better bench vise is one of those shop upgrades that will pay for itself over time. But it was another reminder that “bolt-on” does not always mean “no extra preparation required.”

For the rear springs and shocks, another shout-out goes to WAYALIFE. Eddie Oh’s step-by-step Jeep Wrangler and Gladiator videos are incredibly helpful, especially for suspension work. Seeing the process laid out clearly before crawling under the truck makes a real difference, and his forums and YouTube library of Jeep mod and repair content is one of those resources I found myself going back to during these projects.

Springs: A Mild Refresh, Not a Personality Change

Along with the shocks, I replaced the springs.

Again, the goal was not to radically change the truck. I wasn’t trying to create a monster lift. I wasn’t trying to reinvent the Gladiator’s entire suspension geometry in the driveway.

This was about refreshing worn components, improving ride quality, and giving the truck a little more confidence under its current setup.

My Gladiator is not stock. It has aftermarket steel front and rear bumpers, a winch, 35-inch Nitto Recon Grappler A/T tires, and it often carries camping gear, tools, recovery gear, and other trail/camp essentials.

All of that adds up.

Over time, factory suspension components get tired. Springs settle. Shocks lose their control. The truck may still be drivable, but it doesn’t feel as tight or composed as it once did.

That was the point of this project.

Not a full build.

A refresh.

And there’s a difference.

Tire Rotation While Everything Was Apart

While I was into the suspension work, I went ahead and rotated the tires. This is one of those simple maintenance tasks that is easy to skip, especially when the truck is already apart and you’re tired. But with 35-inch all-terrain tires, regular rotation matters. Big tires are not cheap. Keeping wear even is part of getting the full value out of them. Since I already had the tools out and the truck was up, it made sense to knock it out. That is really the theme of this whole maintenance marathon: stack the jobs that overlap. Spark plugs and oil cooler. Oil cooler and oil change. Suspension and tire rotation. None of these jobs are tiny on their own, but when you plan them together, you make better use of your time and avoid tearing into the same areas repeatedly.

Mission Accomplished

By the time it was all done, I felt like I had been beat with a baseball bat. There was blood — nothing dramatic, just the usual collection of scrapes from sharp metal edges, stubborn brackets, and zip ties that apparently fight back. After a little shakedown driving, and some retorquing in the rear, this job is finished. But in the end, I did it myself, with a little help from some excellent YouTube creators who took the time to make thorough, useful content for the rest of us driveway mechanics. And now, aside from regular oil changes and normal upkeep, my Jeep Gladiator should be good to go for another 50,000 to 60,000 miles before the next high-ticket maintenance item shows up. Yes, that will probably be tires. By then I’ll be somewhere around 180,000 miles, with a handful of new adventures, a few more lessons learned, and hopefully a few good stories to tell.

Tread lightly and Gladiator Up! – Doug

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