Internal Combustion Forklifts

The Pros and Cons of Internal Combustion Forklifts

Internal combustion (IC) forklifts are the backbone of many industrial manufacturing processes, shipping companies, and construction firms. And the reason is pretty simple: there’s no substitute for the IC’s capacity. Capable of lifting pallets, sections of pipeline, and entire shipping containers, IC models heft up to 120,000 lbs and perform far better than their electric counterparts during heavy-duty jobs.

With noticeably faster acceleration and higher travel speeds, internal combustion lifts run on a variety of fuels including gasoline, diesel fuel, liquid propane gas (LPG), or compressed natural gas (CNG). But while they’re capable of an endless variety of earth moving tasks, they do have a number of additional pros and cons that make them suited (and ill-suited) to some applications. These include the following:


  • Quick refuel. Unlike an electric lift that has to be charged for 8 to 16 hours, IC forklifts can be refueled on the fly. Simply fill it up at a gas pump or load a new LPG canister and you’re back on the job.
  • Lower upfront cost. Price points are the inverse of electric – IC lifts are reportedly 20% to 40% less than electric models.
  • All terrain. Designed for outdoors use, IC models are the only types of forklifts capable of operating in extreme environments. Heavy-duty forklift tires and robust designs create models that include high capacity and rough terrain forklifts.


  • Outdoor use only. Of the internal combustion models, only propane-fueled lifts can be used indoors. And even then, they can only be used in areas with ample ventilation. Gas and diesel-powered models are strictly for outdoor use. For indoor/outdoor use, duel fuel systems are available that let you switch between LPG and gasoline.
  • High and fluctuating cost of fuel. Generally speaking, fuel costs are highest for gasoline and lowest for diesel, with LPG falling somewhere in the middle. Fuel costs vary considerably from state to state and fluctuate dramatically depending on the price of oil and other contributing factors.
  • More expensive to operate. With the unpredictable rise and fall of fuel, it’s tough to estimate an exact future cost. But in general, you’ll pay about $30 to fill a 7 gallon diesel tank and $25 to $35 to fill a 33-lb propane tank. With two fuel replacements per day, this averages out to a yearly fuel cost of $15,000 for diesel and about $12,500 for propane.
  • Storage requirements. IC equipment that uses gasoline and diesel fuel requires you to have an area for storage tanks and pumps. In the same way, LPG requires space for the storage of spare tanks (which is often managed by a dealer or third-party propane vendor).

Industrial Truck Association classes

With the above considerations in mind, it’s also important to know that IC lifts are divided by class depending on their different functionalities. To simplify the purchase process, the Industrial Truck Association (ITA) has organized these types into eight classes. Classes 4 through 8 are dedicated to internal combustion forklifts.

Here’s a quick rundown on each class and what you can expect to find within them.

Class 4: Internal-Combustion Engine Trucks-Cushion Tires
With lifting capacities from 3,000 to 15,000 lbs, ITA Class 4 lifts aren’t the strongest of the bunch. But what they lack in strength, they make up for in other key performance issues. Load management systems often include enhanced transmission features that provide improved deceleration and controlled rollback to enhance load handling on inclines and unstable work surfaces. In addition, they usually feature some kind of rubber mat that seals the floor and provides quiet operation as well as additional comfort for the operator.

  • Common applications: indoors, warehousing, food and beverage manufacturing, and rentals

Class 5: Internal Combustion Engine Trucks-Pneumatic Tires
Designed for indoor and outdoor use, IC lift trucks with pneumatic forklift tires are operated via hydraulics and can lift from 3,000 to 19,000 lbs. They typically include user-friendly ergonomic controls as well as an adjustable steer column and multiple configurations for the cab and seat to customize the truck for extended use. Plus, many modern Class 5 lifts feature oil-cooled wet disc brakes for precise stopping power and incorporate a power reversal feature that all but eliminates tire spin, increasing safety while bolstering tire life by up to 50%.

  • Common applications: indoors/outdoors, warehousing, wood pallet/skid manufacturing, and rentals

Class 6: Electric and Internal-Combustion Engine Tow Tractors
Tow tractors transport palletized goods weighing up to 2,000 lbs. Unique among other electric forklifts, they have the ability to form a train, towing multiple trailers at once, and reportedly cost up to 70% less to operate than similar IC models. Powered by a DC traction motor and available in three different types – walkie, walkie-rider, and sit-down rider – tow tractors have a top travel speed of 20 mph or less.

  • Common applications: indoors/outdoors, loading pads, airports, warehouses

Class 7: Rough Terrain Forklift Trucks
Providing a mere 5,000 to 8,000 lbs of lift capacity may not sound like much. But the ability to carry that weight over rocky, muddy, or sloped gradients makes rough terrain forklifts a lot more impressive. Class 7 models often feature a 25 mph drive speed and drive tread widths from 62 to 68 inches. They are also engineered with a compact design and minimal turn radius that provides easy maneuverability on most jobsites. Plus, many models in this category can be customized to include full cab enclosures, extra load cushioning, and a variety of accessories.

  • Common applications: indoors/outdoors, agriculture, oil refineries, construction, and pipe yards

Class 8: Personnel and Burden Carriers
If you’ve been to the airport in the past three decades, you’re well familiar with a personnel/burden carrier. Featuring industrial-grade engineering, they often include dual front wheels for easy operation in any location and a turn radius between 74 to 92 inches. They also offer programmable performance characteristics – like maximum speed and acceleration rate – to cut down on the time it takes to complete recurring tasks. Typically constructed from 10-gauge steel, they’re dressed up with a 14-gauge diamond plate exterior that fends off damage to the body and adds a rugged appearance to the truck. Deck dimensions are commonly 22 inches in height with a platform that measures 31 inches by 48 inches.

  • Common applications: indoors/outdoors, corporate and university campuses, loading pads, airports, warehouses

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