AMC Built A Cast-Iron Inline-Six In 26 Months That Ran Until 2006
There’s a ridiculously cheap and easy way to buy into the 400,000-mile club if you’re so inclined. It involves getting your hands on a 4.0-liter PowerTech inline-six that American Motors Corporation (AMC) built, the same one that was offered in the Jeep snag a Cherokee XJ. This engine spent nearly 20 years on the market, from 1987 to 2006, and it’s not uncommon to hear about them lasting 200,000 to 300,000 miles, as the linked forum shows. Even 500,000 miles in some cases.
That doesn’t mean that they will last that long, just that they can.
How Did The PowerTech Last So Long
A cast-iron engine block and cylinder head, a crankshaft with seven main bearings, and a pushrod valvetrain were all part of the package — a package that evolved from the older 258 cubic-inch inline-six. The 4.0 was developed in just 26 months, evolving from the 258 by using electronic fuel injection and a redesigned cylinder head.
In later years, the High Output versions made 190 hp and 235 lb-ft of torque. Even today, clean XJs can fetch four figures, while functional units can be had for under $1,000. A quick look at Edmunds shows you can get into one in rough shape for under $350 (that’s for a 1991 model year example). The most you might pay is still under $4,000. That allows budget-minded enthusiasts to get into an old rig with a fairly bulletproof engine inexpensively — but beware: if you want to spend under a grand, the condition will be rough. On the other hand, that’s perhaps how you see value — buy cheap and fix it up.
Why The PowerTech Allows You To Go Wheelin’ On The Cheap
Compare that to spending five figures on an old Toyota Land Cruiser. One is absurdly cheap, one isn’t. That being the case, if you’re looking for old-school simplicity and durability, why drop so much money on a Land Cruiser when you can snag a Cherokee for low four figures, or perhaps under a grand? You can also find parts easily, since the production run was so long.
The 4.0 has the distinction of being discontinued due to tightening anti-pollution rules and worn-out factory tooling. Otherwise, it might still be available today. Let’s take a deeper dive into the PowerTech 4.0.
Dollars Per Mile
Let’s take a look at how many dollars per mile the PowerTech can fetch you. Most examples last 200,000 to 300,000 miles, and while 400,000+ miles isn’t guaranteed, it’s possible.
We’ll use this equation: Purchase price ÷ target mileage = acquisition dollars per mile. We’ll take a look at the PowerTech 4.0-liter, as well as Ford’s 300 inline-six, Chevrolet’s 292 inline-six, and the Toyota 1HZ.
In the case of the PowerTech, we can use an example like the one featured at Tread.com that was picked up for $450, something that’s not entirely uncommon today. Let’s say we’ve done the same, with the goal of going 300,000 miles. Even if it already has 150,000 miles on it, we’re making out. $450 divided by 150,000 equals $0.003 per mile. Compare that to the Toyota, which might cost, say, $40,000 (like this example) but could rack up 500,000 miles. That’s a cost of $0.10 per mile starting from the 125,000-mile odometer reading.
Questions exist that one should ask themselves for each engine. For the XJ, the question is how much durability can a small cash outlay buy? For the Ford, you’re asking if greater scarcity hurts value, and for the Chevy, you’re asking about the vehicle’s age, since an older vehicle will make vehicle condition more important. Finally, for the Land Cruiser, you’re asking if diesel longevity is worth the price of entry.
The Ford will cost a little more than the PowerTech, while pricing on the Chevy varies.
Production Years: 1987–2006
It all started with American Motors Corporation in 1964, when the company introduced what was then considered to be a modern inline-six, this one displacing 199 cubic inches. Eventually, it grew to 232 cubic inches and then 258 CID, or 4.2 liters. An increased bore and shortened stroke led to the 4.0. A revised cylinder head was installed to match with the updated architecture.
This made the PowerTech more evolutionary than revolutionary. It wasn’t a clean-sheet design. This could explain why the engine was developed in just 26 months.
Early on, the 4.0 ran a Renault/Renix fuel injection system to replace carburation, but once Chrysler (now Stellantis) took over AMC fully in 1991, it put its own system in. Cold starts, idle quality, and emissions regulations compliance improved, as did horsepower. That number jumped to 190 by 1991. The engine was built in Kenosha, Wisconsin, at a clip of 405,000 units per year.
How Staying The Course Became The Secret To Longevity
We mentioned the 4.0-liter’s cast-iron block earlier, and that engine block was a key factor in this inline-six’s two-decade run of success.
That heavy-duty, cast-iron construction creates strength, durability, resistance to distortion, and the ability to withstand repeated heat cycles and last for many miles.
That’s why the cylinder head was also cast-iron. It, too, had the same abilities as the block. But that doesn’t mean every cylinder head is bulletproof. Sometimes they do break or crack, so nothing is guaranteed. Being less likely to have damage doesn’t mean it won’t sustain damage.
The seven-main-bearing crankshaft is also part of the durability story, and having the additional main-bearing support helps keep the crankshaft stabilized. It also helps distribute loads, which keeps any single part of the crankshaft from being overstressed, which could lead to damage.
With its pushrod overhead-valve setup, the engine kept the camshaft in the engine block, using rocker arms and two valves per cylinder.
Keeping the engine simple with fewer components meant fewer problems: with fewer moving parts and less complexity, there were fewer things that could break.
While the powertrain put out horsepower numbers that are modest by modern standards, there was a benefit to this relative lack of power. Since this engine wasn’t developed for speed, but rather to get a four-by-four moving across road and trail, it could be built simply, with a focus on reliability instead of using complexity to create performance.
The XJ Was The Perfect Delivery System
If the PowerTech was one of the best engines for off-road reliability, it was also mated to its perfect partner. The Cherokee’s compact dimensions, excellent off-road capability, light weight, simple mechanical layout, and a large aftermarket filled with inexpensive pre-owned units all contributed to the Cherokee name’s fame. That fame, that success of the model, helped make the engine famous. It was a hand-in-hand situation — the engine made the Cherokee successful, while the Cherokee’s success drew attention to the engine and made it famous.
That said, it’s important to note the engine outlived the Cherokee XJ. That model ended in 2001. But the 4.0-liter inline-six continued in other Jeeps, like the TJ Wrangler, until 2006.
Vehicle Versus Engine
While we’re on the subject of reliability, don’t confuse engine reliability with vehicle reliability. Even if the engine is reliable and not experiencing any problems, Jeeps, especially the Cherokee XJ, have had issues with unibody rust, the so-called “death wobble,” suspension wear, electrical problems, and cooling-system problems.
So, the engine might be durable, but the rest of the vehicle might not be even close to indestructible. If you buy a Cherokee XJ, keep that in mind. It’s more that you’re buying access to a highly reliable engine than a highly reliable vehicle.
The $450 XJ Problem: The Engine Isn’t The Expensive Part
Understanding that the engine’s reliability is separate from the rest of the vehicle’s, you may find yourself spending money on repairs that don’t involve the PowerTech. You might be inspecting the body for rust or replacing worn suspension bits. You could be maintaining the A/C system or dealing with electrical woes.
You can’t think of the price of the vehicle as your total cost of ownership — in addition to unavoidable ownership costs like gas, insurance, and maintenance, you may also have the cost of repair for non-engine components of the vehicle.
The trick isn’t to find a cheap Jeep that costs nothing beyond the purchase price. The trick is to find one whose problems won’t come from the engine, which is the one part you expect to last.
Why Jeep Finally Killed It
We hinted at it above, but the PowerTech died not because it was no longer reliable, but because of regulations. Tightening nitrogen oxide regulations were among the causes of death. Not only that, but the engine’s architecture itself was aging, and the tooling needed to produce these engines was also reaching the end of its life.
It would be too easy to say Jeep replaced the PowerTech 4.0-liter inline-six with newer technology, but the truth is that there was no longer a business case for producing the engine. Updating the tooling, modernizing the cast-iron architecture, and making the engine compliant with tightening emission regulations would cost more than the company could earn back in sales.
500,000 Miles Is The Ceiling But Not Common
While 500,000 miles is a possibility with these engines, keep your expectations reasonable. Two hundred thousand is a nice benchmark, with 300K miles relatively routine. Four-hundred-thousand miles is not an unrealistic target. But there are documented examples of these engines and vehicles reaching half a million miles or more. So it’s possible to cross the 500,000-mile barrier, but don’t expect it to be a given.
Still, it all comes together to give you a low barrier to durable off-roading. The durable engine and the low purchase price give you a chance to get an off-roader that lasts, provided you’ve made sure the rest of the vehicle is also in good shape.
You may or may not make it to 500,000 miles, but you’re in the club without spending the money required to purchase a Toyota Land Cruiser.
For many, that’s a win.
Sources: Edmunds, Tread.com, Cherokee Forum, Jeep,
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