How to Fuel and Refuel Rented Equipment

Two reasons to read this before you return rented equipment. The financial one: many rental partners charge a refueling fee — typically well above the pump price — when equipment comes back below the fuel level it went out at. On a machine with a 15–25-gallon diesel tank, the difference between filling it yourself and letting the rental partner fill it can run $30–$100 or more depending on the fee structure. Check your rental agreement for the specific fuel policy before the rental ends — the Big Rentals FAQ covers platform-level guidance on rental terms. The practical one: knowing where the fuel intake is, what goes in it and what diesel exhaust fluid (DEF) is before you're standing next to an unfamiliar machine in the field.

Fuel Types on Common Rental Equipment

Know the fuel type before you look for the intake

Most construction equipment available through the Big Rentals marketplace runs on diesel — mini excavators, skid steers, compact track loaders, telehandlers, larger forklifts and larger aerial lifts all typically run on diesel. Smaller walk-behind trenchers and some light-duty equipment run on gasoline. Propane forklifts use a propane cylinder that swaps out rather than a tank that fills at a pump. Many indoor scissor lifts and compact forklifts are electric — they charge from an outlet rather than fuel at a pump.

The simplest way to confirm the fuel type before searching for the intake: look at the fuel cap. Most equipment fuel caps are labeled with the fuel type, or use color coding. Diesel caps are often green or black. DEF caps — a separate tank present on most modern diesel machines — are almost always blue. If the cap isn't labeled and the operator's manual isn't in the cab, ask the rental partner at pickup. Never guess on fuel type. Putting gasoline in a diesel engine or diesel in a gasoline engine causes serious and expensive damage.

• Diesel: mini excavators, skid steers, CTLs, telehandlers, larger forklifts, diesel boom lifts
• Gasoline: some smaller walk-behind trenchers and light-duty equipment
• Propane: propane forklifts and some aerial lifts — cylinder swap, not pump fueling
• Electric: many compact scissor lifts, some indoor forklifts — charge from an outlet
• When uncertain: check the cap label, check the operator's manual or ask the rental partner at pickup

Where Fuel Intakes Are Located by Equipment Type

Mini excavators

On most mini excavators, the fuel cap is on the right side of the upper house — the rotating cabin section — behind a hinged service panel that opens outward. Unlatch or lift the panel and the fuel cap is at the top of the tank, accessible from a standing position alongside the machine. Many models have a sight glass on the fuel tank visible from outside the panel — useful for checking the level without removing the cap. A DEF cap (blue) is often visible in the same service area on Tier 4 final diesel machines. Fill the fuel tank through the fuel cap only.

• Location: right side of the upper house, behind the hinged service panel
• Access: unlatch or lift the panel; fuel cap is at the top of the tank
• Sight glass: visible on many models from outside the panel — check level before removing the cap
• DEF: blue cap, same service area — separate tank, do not confuse with the fuel cap

Skid steers and compact track loaders

The fuel cap on most skid steers and compact track loaders is at the rear of the machine, behind the cab, accessed through the rear service door. The rear door hinges open to expose the engine compartment — the fuel cap is at the top of the fuel tank, which sits between the machine's rear frame uprights. On some models, a separate side panel on the right gives access to the fuel cap without opening the full rear door. The rear service compartment also contains the hydraulic fluid reservoir, engine oil and coolant — confirm you're at the fuel cap before filling. The fuel cap is labeled on most machines.

• Location: rear of the machine, behind the cab, accessed through the rear service door or side panel
• Access: open the hinged rear door; fuel cap is at the top of the tank in the rear service compartment
• Confirm the cap: multiple fluid caps are in the same area — fuel cap is labeled; don't fill the hydraulic reservoir
• DEF: blue cap, same rear service area on Tier 4 final diesel machines

Telehandlers

On most telehandlers, the fuel cap is accessed from the right side of the machine at the engine compartment — a hinged panel at approximately standing height opens to expose the engine area and the fuel cap. Some models access from the left side or rear. The fuel gauge in the cab is the quickest way to check the fuel level without opening any panels. DEF cap (blue) is typically in the same engine compartment area. Telehandler engine compartment layouts vary more by manufacturer than mini excavators or skid steers — confirm the specific access point at pickup.

• Location: typically right side of the machine, engine compartment area behind a hinged panel at standing height
• Fuel gauge: instrument panel in the cab — check level here before opening panels
• DEF: blue cap, same engine compartment area
• Confirm at pickup: layouts vary by manufacturer — ask the rental partner where the fuel cap is on the specific unit

Diesel forklifts

Diesel forklifts typically have the fuel cap accessible from one side of the machine near the engine compartment — often at the counterweight end or along the side frame, reachable from ground level. The fuel gauge is on the instrument panel in the operator compartment. On machines with Tier 4 final diesel engines, a DEF cap (blue) is present in the engine compartment area. Forklift designs vary significantly by manufacturer and capacity class — confirm the fuel cap location with the rental partner at pickup on any unfamiliar unit.

• Location: side or rear of the machine at the engine compartment, accessible from ground level
• Fuel gauge: instrument panel in the operator compartment
• DEF: blue cap, engine compartment area on Tier 4 final machines
• Confirm at pickup: layouts vary significantly by manufacturer and capacity class

Propane forklifts

Propane forklifts don't have a fuel tank to fill at a pump. They run on a liquid propane cylinder — typically a 33-lb cylinder — mounted in a bracket at the rear of the machine, often on or near the counterweight. When the cylinder runs low, the whole cylinder is swapped for a full one. Propane cylinders can be exchanged at most propane suppliers and many hardware stores. Confirm the cylinder size with the rental partner so you bring the correct replacement. Do not attempt to partially refill a forklift propane cylinder in the field from a portable tank — cylinder-to-cylinder propane transfer without proper equipment is unsafe.

• No pump fueling: cylinder swap only — not a tank that fills at a gas station
• Cylinder location: rear of the machine, in a bracket on or near the counterweight
• Exchange: 33-lb cylinder typically; confirm size with rental partner; exchange at propane suppliers or hardware stores
• Do not partially refill in the field: cylinder-to-cylinder transfer without proper equipment is unsafe

Electric scissor lifts and electric forklifts

Electric machines charge from an outlet rather than fuel at a pump. The charging port on most electric scissor lifts is on the base of the machine — front, rear or side depending on the manufacturer — covered by a small hinged door or rubber plug. On electric forklifts, the charging port is typically under the hood or behind a panel at the engine compartment area. Most use the onboard charger cable stored on the machine or supplied with it. Full recharge from a depleted battery takes 8–12 hours — overnight charging is the standard practice on rental equipment. Return electric machines with an adequate charge; some rental partners charge a fee for batteries returned in a deeply discharged state.

• No fuel: electric machines charge via battery — no pump, no cylinder
• Charging port (scissor lift): base of the machine, front, rear or side, under a small door or rubber plug
• Charging port (electric forklift): under the hood or behind a panel in the engine compartment area
• Charge time: 8–12 hours for full recharge — plan overnight charging on multi-day rentals
• Return full: deeply discharged batteries may incur a fee — charge overnight before the return date

Diesel boom lifts

Diesel boom lifts have the fuel cap on the base of the machine — the turntable or chassis section — typically on one side at approximately ground level. An engine compartment panel opens to expose the fuel cap and other service points. The fuel gauge is visible on the ground-level control panel. For propane boom lifts, the propane cylinder is mounted on the base — same cylinder-swap procedure as propane forklifts. Electric boom lifts have a charging port on the base or chassis in approximately the same location where a diesel model would have a fuel cap.

• Diesel: fuel cap on the base of the machine (turntable or chassis), behind an engine compartment panel, accessible at ground level
• Fuel gauge: ground-level control panel — check here before opening engine compartment
• Propane: cylinder on the base of the machine — swap procedure same as propane forklifts
• Electric: charging port on the base or chassis, same general location as the diesel fuel cap

DEF: The Fluid Most Renters Confuse for Fuel

DEF goes in the blue-capped tank — never in the fuel tank

Most diesel construction equipment built after 2011 — and virtually all current-production diesel rental equipment — has a diesel exhaust fluid (DEF) system alongside the fuel system. DEF is a clear solution used by the engine's emissions control system. It is not a fuel additive and it does not go in the fuel tank. It has its own separate tank, identified by a blue cap, typically located near the fuel cap in the engine compartment or service area.

Running out of DEF causes most modern diesel machines to reduce power (called derate) or shut down completely — the emissions system requires DEF to operate the engine above low-power mode. DEF is widely available at truck stops, fuel stations and auto parts stores in clearly labeled blue jugs. Check the DEF level whenever you refuel. If the DEF tank is low, fill it on the same service stop — a machine that shuts down for low DEF on a job site requires a recovery visit, not just a quick fix.

• What it is: diesel exhaust fluid — used by the emissions control system, not the fuel system
• Where it goes: separate DEF tank, always identified by a blue cap — not in the diesel fuel tank
• Consequence of running out: engine derate (power reduction) or shutdown on most modern diesel machines
• Where to buy: truck stops, fuel stations and auto parts stores — clearly labeled blue jugs
• Critical: do not put DEF in the fuel tank; do not put diesel in the DEF tank — both cause serious engine damage
• Check with every fuel stop: same service visit, blue cap, separate tank

Practical Refueling Notes

A few things to know before you refuel

Construction equipment fuel caps often have a built-in strainer screen inside the cap opening. When inserting the pump nozzle, push it in firmly past the screen — a loose contact with the screen surface causes the pump to click off repeatedly as though the tank is full. Push past it and the nozzle seats correctly.

Don't overfill in hot weather. Diesel and gasoline expand as temperature rises. Fill to approximately 95% capacity in hot conditions — a completely full tank in the morning can overflow by midday if temperatures climb.

Clean any diesel spills immediately. Diesel appears dry before it fully evaporates and is a slip hazard on metal steps, decks and ground surfaces. Wipe any spill before walking on it or before other workers come near.

If the rental agreement requires a fuel receipt as proof of refueling, save it. A photo of the fuel gauge alongside the pump receipt is the most useful documentation if questions arise.

Let a machine that's been working hard cool for 10–15 minutes before opening the fuel cap. Opening the cap on a pressurized hot tank causes fuel to spit from the opening.

• Strainer screen: push the nozzle firmly past the screen inside the cap — loose contact makes the pump click off prematurely
• Hot weather fill: fill to approximately 95% capacity — fuel expands and a full tank overflows as temperature rises
• Spill cleanup: diesel on walking surfaces is a slip hazard before it dries — clean any spill immediately
• Receipt: save the receipt and photograph the gauge if the rental agreement requires proof of refueling
• Cool down: 10–15 minutes after hard operation before opening the fuel cap — pressurized hot tanks spit fuel

The Short Version

Confirm the fuel type before looking for the intake — diesel on most construction equipment, propane cylinder swap on propane forklifts, outlet charging on electric machines. The fuel cap is typically in the rear service compartment on skid steers and CTLs, the right-side service panel on mini excavators, the engine compartment on telehandlers and forklifts, and the base of the machine on boom lifts. On any modern diesel machine, the blue-capped DEF tank is separate from the fuel tank — fill both, confuse neither. And return the machine at the same fuel level it left — it's consistently cheaper than the alternative.

Questions about your specific rental agreement's fuel policy? Review your rental agreement or visit the Big Rentals FAQ.