The Eco Extreme 1 Change 1 Tank Challenge with the BYD SEALION 5 DM-i saw automotive media and influencers testing fuel efficiency at low speeds. Overall, results aligned consistently: the BYD SEALION 5 DM-i in this record-breaking fuel-saving event, in collaboration with BYD, journeyed across regions—from the northern highlands down to Thailand's top southern tourist city. Using the BYD SEALION 5 DM-i equipped with the DM-i PHEV system, the car almost exclusively ran in EV mode at low, gentle speeds, traveling long distances purely on electric motor power. When the battery drained, the large battery prompted the 1.5-liter Xiaoyun engine to generate electricity at very low, steady RPMs—the most fuel-efficient range—claiming figures of 25–27 kilometers per liter comfortably. Read on to see why it felt so effortless.
This marathon test, spanning day and night from Chiang Mai to Phuket with the BYD SEALION 5 DM-i, was part of the Eco Extreme 1 Change 1 Tank Challenge—BYD's mission to extract every last drop of fuel from the SEALION 5 DM-i. The route was mapped to prove endurance and set a historic benchmark in extreme fuel economy testing. The test involved driving at low speeds across regions—from the northernmost peaks of Thailand to the southern Andaman coast—in one continuous stretch from Chiang Mai to Phuket, covering over 1,500 kilometers and pushing engineering and long-distance testing boundaries.
The Eco Extreme 1 Change 1 Tank Challenge required maintaining a constant throttle between 40-60 km/h for two full days. The first leg followed the northern terrain along Highway 11 (Super Highway), starting from a hotel in Chiang Mai, heading towards Lamphun province, then climbing over Khun Tan mountain to Lampang. The convoy then merged onto the Northern Expressway to join Phahonyothin Road (Highway 1), pressing on through Tak, Kamphaeng Phet, and Nakhon Sawan, using bypass routes like Highway 122 before rejoining Asian Highway 32. The steady speed cruise continued through Chainat, Singburi, Ang Thong, and Ayutthaya, entering the Kanchanaphisek Ring Road (Highway 9), and heading towards the Bang Bua Thong/Bang Yai area.
In the second leg, the route passed Ratchaburi heading south. Upon reaching Bang Yai, the convoy turned southward, taking the M81 expressway, exiting at Si Sa Thong toll gate to connect with Phet Kasem Road (Highway 4). Passing through Nakhon Pathom, Ratchaburi, and Phetchaburi, the route diverted onto the Cha-am–Hua Hin bypass (Highway 37), proceeding to Pranburi before rejoining the main Phet Kasem highway. The drive continued, battling fatigue and drowsiness through Prachuap Khiri Khan and Chumphon provinces.
The third leg pierced through the Andaman region, crossing Sarasin Bridge to the final destination. Upon reaching Pathomphon intersection, the convoy switched to Highway 41 toward Surat Thani, then turned onto the Southern Seaboard route (Highway 44), heading straight to the end at Ao Luk in Krabi province. The convoy then reversed onto Highway 4 for about 13 kilometers before turning left onto Route 1002 toward Phang Nga province. Rejoining Highway 4 again, the journey continued to Phuket province, following routes 4303 and 402 respectively. The SEALION 5 DM-i crossed the iconic Sarasin Bridge, a landmark of the Andaman Pearl, arriving at the final stop—Homa Phuket Town Hotel. The route was deliberately designed to avoid shortcuts, favoring bypass and detour roads to maintain a steady speed between 40-60 km/h over a total distance of 1,847 kilometers, making the 33.6 km/l fuel economy not just a figure but a monument to endurance.
DM-i, or Dual Mode - intelligent, is BYD's plug-in hybrid propulsion technology designed primarily for electric-first hybrid vehicles. BYD cars using this system rely on a large battery combined with a high-performance electric motor as the main drive source. The 1.5-liter internal combustion engine, with high thermal efficiency, acts mainly as a generator to extend range or boost power when accelerating or overtaking. DM-i plug-in hybrids provide a driving experience similar to pure electric vehicles, offering extended overall range at low speeds with very low fuel consumption during long-distance travel.
BYD's advanced DM-i plug-in hybrid technology represents a futuristic approach, offering an environmentally conscious alternative as global awareness grows. The automotive industry is rapidly adapting to rising fuel prices and environmental demands. Among current innovations, BYD's DM-i stands out as an intelligent plug-in hybrid system that breaks traditional rules by prioritizing electric drive. DM-i is a game-changer appealing to performance enthusiasts and eco-conscious younger drivers alike, seamlessly switching between electric and fuel power without compromise. Its fresh engineering and comprehensive energy management make BYD DM-i a hybrid powertrain well-suited for today's evolving automotive landscape.
The engineering structure of BYD's DM-i electric heart plug-in hybrid system is fundamentally different from traditional hybrids. Most conventional hybrids rely primarily on the internal combustion engine for power, whereas DM-i prioritizes electric drive through a high-performance motor and large battery. The gasoline engine's role is reduced to that of a generator, resulting in quieter, smoother driving—especially at low speeds where electric power dominates completely. For example, the BYD Tang DM-i can run over 115 kilometers purely on electric power, making urban commutes or errands easy without frequent gas stops. Besides charging the battery, the engine also supplements torque rather than just generating electricity like a typical range extender.
The DM-i system’s plug-in hybrid powertrain components work in harmony with a highly stable electric motor designed to spin up to 16,000 rpm, achieving 97.5% efficiency. This means nearly all electrical energy converts directly into torque at the wheels with minimal loss. The motor and engine provide quick response, enabling 0-100 km/h acceleration in 8.5 seconds for a mid-size SUV comparable in size to the Honda CR-V. The Blade Battery uses a lithium iron phosphate (LFP) design that is heat-resistant and durable, with high energy density supporting efficient charging and discharging.
The endurance of the 18.3 kWh Blade Battery, managed by the DM-i energy allocation system, is key to enhancing overall vehicle performance. The Xiaoyun Engine, developed specifically for fuel efficiency, boasts a brake thermal efficiency of 43%. The 1.5-liter engine operates smartly—not just running continuously but engaging when battery charge is low or when extra torque is needed. It maintains low fuel consumption as expected, making low-speed driving exceptionally economical.
The Xiaoyun Engine (骁云 in Chinese) is a modern internal combustion engine developed by BYD as a critical component in their DM-i and DM-p plug-in hybrid drivetrains. Unlike conventional plug-in hybrids, this engine is engineered primarily as a high-efficiency generator to supply power back to the battery and electric motor in the hybrid system, while also supplementing torque. What makes the Xiaoyun Engine notable in the automotive world is its high brake thermal efficiency of 43%, a figure that surpasses typical market engines, which usually achieve 30–35%. This makes it one of the most energy-efficient engines globally today.
This engine uses the Atkinson Cycle with variable valve timing to align intake and ignition for maximum fuel economy. Though it lacks a turbocharger and delivers modest low-end torque—making it seem sluggish if used alone in a conventional car—when paired with the DM-i system’s electric motor assistance from startup to cruising speeds, the Xiaoyun Engine operates at steady, fuel-efficient RPMs primarily to generate electricity.
To reduce internal friction, the Xiaoyun Engine omits many traditional auxiliary components since the DM-i’s high-voltage electric system manages energy. It eliminates the conventional starter, using an electric motor for engine start instead. There is no belt-driven water pump or oil pump, and the air conditioning compressor is electric. Removing unnecessary parts lowers friction, making the engine run smoothly, quietly, and with low fuel consumption even when battery charge is low. In simple terms, the Xiaoyun Engine is a compact, fuel-efficient, intelligent mobile power plant, essential to BYD SEALION 5 DM-i’s record-breaking fuel efficiency.
The intelligent control system is the electronic brain of the DM-i technology, automatically switching between electric and fuel power based on speed and battery charge. When expertly programmed, this system makes BYD’s DM-i stand out for fuel economy. BYD plug-in hybrids with DM-i powertrains can achieve remarkably low fuel consumption—just 3.8 liters per 100 kilometers (about 26.3 km/l) at low speeds of 40-50 km/h. This level challenges competitors in the segment. Even as battery power depletes, the system maintains low fuel use, benefiting both wallets and environmental goals by reducing carbon emissions. The seamless transition between electric and fuel modes ensures smooth driving.
The DM-i system is designed to deliver an electric-first driving experience as follows:
When the battery is fully charged, the vehicle operates like a pure electric car (Pure EV), ideal for city driving. When battery charge is low, the engine starts to recharge the battery or assist propulsion. The intelligent energy management system automatically balances battery, motor, and engine operation to maximize fuel efficiency while maintaining responsive performance.
Four main driving modes
The system supports four distinct driving scenarios:
EV Mode: The car runs solely on electric power without using any fuel, as long as the battery has charge.
Series Mode: The engine powers a generator to charge the battery or directly supply electricity to the motor; the wheels are driven exclusively by the electric motor. This mode suits long-distance highway driving.
Boost Mode: The engine and electric motor work together to deliver powerful acceleration, with the engine also charging the battery as needed.
Charge Mode: The engine charges the battery during driving to preserve electric-only range for later use.
All these modes operate automatically to provide smooth, simple, and enjoyable driving.
Benefits of the BYD DMi plug-in hybrid system combining engine and electric motor power include primarily electric driving from the 18 kWh battery at low speeds (70-80 km/h). During long-distance travel, the DMi PHEV achieves significantly better fuel consumption than REEV or HEV systems, although it works best below 80-90 km/h, which aligns with typical traffic speeds.
Performance and response are good, with 0-100 km/h acceleration in 8.5 seconds, not sluggish. The 1.5-liter engine reduces emissions and works with intelligent energy management for optimal fuel use. The software and DMi PHEV powertrain work seamlessly, offering smooth and quiet driving at low speeds. BYD’s battery technology is safe and reliable, supporting DC charging but not at extremely fast rates. The car suits drivers who keep speeds below 80-90 km/h to maximize fuel savings. DMi’s advantages stem from carefully designed complex systems working harmoniously.
Blade Battery
Electric Motor
Internal Combustion Engine (ICE)
Intelligent Energy Management System (IEMS)
Power Electronics/Inverter System
Transmission/Gearbox
Cooling Systems
DM-i technology merges the best of both worlds: an internal combustion engine generating electricity and assisting torque when overtaking, combined with electric vehicle efficiency. It achieves high performance but can cover 1,400 to 1,500 kilometers on a full fuel tank and battery charge.
The BYD SEALION 5 DM-i Eco Extreme Challenge was a long-distance fuel-saving test. The car was comfortable and easy to drive, but the drivers and support team endured a grueling distance and schedule. Using the DM-i Super PHEV system, the vehicle ran mostly in EV mode at low speeds around 50 km/h, with the driver managing throttle from start to finish, extracting maximum range from one tank of fuel and a full battery. Over the 1,847 km from Chiang Mai to Phuket, the engine engaged briefly to generate electricity with gentle regeneration. Even when the battery depleted, the 1.5-liter Xiaoyun engine ran at low, steady RPMs to recharge the battery efficiently, claiming 25–27 km/l for two other competing vehicles that started ahead. The winning vehicle achieved an astounding 33.7 km/l. The longer distance than the usual 1,500 km from Chiang Mai to Phuket resulted from deliberately running the car until fuel and battery were completely drained, totaling 1,847 km.
This tough fuel economy challenge was a test every automotive journalist wanted to conquer. Simply reaching Phuket was a difficult goal, as speeds over 90 km/h risked not completing the 1,500 km journey on one tank. Driving at 40–50 km/h for 14–16 hours daily tested driver focus and team endurance, requiring shifts at the wheel. Controlling the accelerator steadily and avoiding RPM spikes to maximize every drop of fuel from the 52-liter tank over 1,847 km was a stressful and exhausting task.
To verify the 1,000+ km claim, BYD states the SEALION 5 DM-i plug-in hybrid can cover 1,000 to 1,200 km on a full tank and battery. Media teams competing drove steadily at low speeds, making a new record on the car's dashboard undeniable. Both teams endured long shifts, with the winning vehicle covering nearly 1,900 km. The fuel tank emptied in Phuket city with 5 liters remaining and 50% battery, after which the team burned off remaining fuel and battery power around Phuket Island overnight. When engine fuel was exhausted, the battery powered the motor to reach 1,847 km total.
Driving at 40-60 km/h is mentally demanding, with boredom and frustration appearing continuously. However, this low speed was the key to victory. BYD set a maximum test speed of 70-80 km/h, meaning competitors had to drive slower to win. Maintaining 40-60 km/h is a sweet spot for the DM-i Super PHEV system, minimizing wind resistance and electric motor load, allowing the engine to generate electricity at low RPMs or not run at all, achieving long pure EV driving.
At 80-90 km/h, wind resistance increases sharply, causing the motor to consume more power and the engine to run continuously, causing fuel economy to drop immediately. The test's goal was to win by driving 40-60 km/h, a strategy aligned with automotive engineering principles. Increasing speed to 70 km/h or above raises the chance of losing to other competitors.
An unusual rule mandated setting the air conditioning to 25 degrees Celsius. Modern electric and hybrid car AC compressors draw power directly from the high-voltage battery, so stronger cooling drains battery faster and causes the engine to start more often. Keeping AC at 25 degrees was a strict requirement for the Eco Run. Those preferring colder AC found it frustrating. Additionally, forbidding phone charging, although theoretically negligible in power draw, was a psychological tactic to save even the smallest fraction of energy, understandable from a competitive viewpoint despite being overly strict from an engineering perspective.
Another team rule limited bathroom breaks to every 3-4 hours to maintain continuous driving momentum. This affected fuel economy significantly because PHEVs consume the most energy during stop-and-go. Frequent stops require braking, idling, and accelerating back to 40-60 km/h, which immediately lowers average fuel economy. Extending driving intervals to 4 hours between breaks helped preserve momentum and minimize energy loss. It may seem extreme but proved effective.
From a competitive mindset, only teams determined to win executed all these strategies and thoroughly understood the complex DM-i system’s operation. All four competing cars sacrificed comfort to achieve the best possible fuel economy records. Teams that drove casually, stopped more, or drove faster would lose immediately, with fuel running out before reaching Phuket.
This test was harsh and unlike everyday driving. Sitting in a car 14-16 hours daily with limited movement, warm AC, and no charging caused stress and health risks, including drowsiness and muscle strain. While the team’s drive for victory was justified, they overlooked crew well-being. I can honestly say the 'golden body' of our driver is now more like a crumpled scroll.
The display showed a total driving distance of 1,847 kilometers.
The 1,847 km driven far exceeded the usual Chiang Mai to Phuket distance of about 1,500 km, due to intentional detours to exhaust fuel completely. The average speed of 51.0 km/h proves the steady throttle control between 40–60 km/h over two full days. The zero kilowatt-hours charged confirms the rule forbidding refueling or recharging was strictly followed—fuel alone powered the battery recharge. Total fuel consumption was 54.9 liters. If the engine could talk, it might complain about being starved of fuel.
This vehicle's fuel tank capacity is approximately 53 liters, filled to overflowing before departure from Chiang Mai. Total fuel used was 54.9 liters. Dividing the 1,847 km traveled by 54.9 liters results in an astonishing 33.64 km per liter. Remember, the BYD SEALION 5 DM-i is a mid-size SUV similar in size to the CR-V, weighing 1.7 tons, yet achieved this extraordinary fuel economy in the challenge. The display also showed an average fuel consumption (AFC) of 3.6 L/100 km. From an engineering perspective, this DM-i system proves that controlling speed within the ideal range yields frighteningly high fuel efficiency. However, from the driver's and passenger's perspective, the 1,847 km distance at a 51 km/h average speed represents a monument to the endurance and patience of all four competing teams. Rules like setting AC to 25 degrees, banning phone charging, restricting bathroom breaks, and avoiding deep throttle resulted in historic fuel economy records.
For the long Eco Extreme 1 Change 1 Tank Challenge trip from Chiang Mai to Phuket, automotive media unanimously agreed the DM-i Super PHEV system is genuinely effective at maximizing fuel efficiency. Under controlled speeds, the SEALION 5 DM-i achieved over 1,000 km on one tank of fuel (about 53 liters) plus an 18.3 kWh Blade Battery, reaching 1,000 to 1,200 km in real conditions. In everyday driving at normal speeds of 100-110 km/h, the vehicle still delivered 23-25 km/l. At 110-120 km/h on the highway, fuel economy dropped naturally but remained around 20-21 km/l—still more efficient than conventional gasoline or HEV SUVs in the same class.
BYD SEALION 5 DM-i Pricing
DYNAMIC model priced at 759,900 baht, offering combined electric and fuel range over 1,200 km plus 110 km pure electric range.
PREMIUM model priced at 799,900 baht, offering combined electric and fuel range over 1,200 km plus 110 km pure electric range.
Dimensions and Weight
Length: 4,735 millimeters
Width: 1,860 millimeters
Height: 1,710 millimeters
Front/Rear track width: 1,575 / 1,585 millimeters
Wheelbase: 2,712 millimeters
Ground clearance without load: 175 millimeters
Ground clearance with maximum load: 156 millimeters
Minimum cargo capacity: 530 liters
Maximum cargo capacity: 1,482 liters
Curb weight: 1,720 kilograms
Gross vehicle weight rating: 2,130 kilograms
Electric motor type: Front permanent magnet synchronous motor (PMS)
Drive system: Front-wheel drive
Maximum front motor power: 120 kilowatts
Maximum front motor torque: 210 Newton-meters
Engine type: 1.5-liter Xiaoyun plug-in hybrid engine
Maximum engine power: 73 kilowatts
Maximum engine torque: 125 Newton-meters
Maximum combined power: 155 kilowatts
Maximum combined torque: 210 Newton-meters
Fuel tank capacity: 52 liters
Acceleration 0-100 kilometers per hour
Battery and Charging
Battery type: BYD Blade Battery
Maximum battery capacity: 18.3 kilowatt-hours
Maximum electric-only range (NEDC standard): 110 kilometers
Portable charging cable (Mode 2)
Supports AC Type 2 charging (maximum 3.3 kW)
Supports DC CCS2 fast charging (maximum 18 kW)
Vehicle-to-Load (VtoL) system
Accessories for VtoL system
Braking system with automatic regenerative energy recovery
Suspension and Brakes
Front suspension: MacPherson strut
Rear suspension: Multi-link
Front brakes: Ventilated disc brakes
Rear brakes: Disc brakes
Wheel type: Alloy wheels
Tire size: 225/60 R18
Emergency tire repair kit
Exterior Standard Equipment
LED headlights
Automatic headlight on/off system
Follow-Me-Home delayed headlight off function
LED daytime running lights
LED taillights
Sequential rear turn signals
LED third brake light
Rear fog lights
Power-adjustable side mirrors with heating and defogging
Power-folding and auto-folding side mirrors
Puddle lights on side mirrors
Power rear tailgate unlock
One-touch power open/close rear tailgate
Roof rails
Automatic windshield wipers
Rear windshield wiper
Interior Standard Equipment
Multifunction steering wheel
Electric power steering (C-EPS)
8.8-inch LCD driver instrument cluster
Front map lights
Rear passenger map lights
One-touch automatic power windows with anti-pinch front and rear
Center console storage compartment
Overhead sunglasses holder
Seating capacity: 5
Synthetic leather seats
6-way power-adjustable driver seat
4-way power-adjustable front passenger seat
Ventilated front seats
60/40 split-folding rear seatbacks
Rear armrest with two cup holders
Front sun visors with mirrors and lights
Puddle lights for front occupants
Cargo area lighting
ISOFIX child seat anchors
Multimedia and Convenience Features
12.8-inch touchscreen multimedia system
Bluetooth mobile phone connectivity
Supports Apple CarPlay® and Android Auto™
FM radio
Eight-speaker audio system
Thai/English voice command system
Music streaming
One USB-C and one USB-A port for front passengers
One USB-C and one USB-A port for rear passengers
Wireless phone charging
12V power outlet
Automatic climate control
PM 2.5 air filtration system
Rear center air vents
Keyless entry and start system
NFC card electronic key system
Bluetooth key
BYD Digital Key
Internet connectivity for BYD app and over-the-air (OTA) software updates
Supports OTA software updates via internet connection
Safety Features
Front airbags for driver and front passenger
Side airbags for front driver and passenger
Side curtain airbags for front and rear
Seatbelt reminder system for front and rear seats
Tire pressure monitoring system (TPMS)
Anti-lock braking system (ABS)
Electronic stability control (ESC)
Intelligent brake assist system
Brake hold system (CDP)
Vehicle dynamic control (VDC)
Electronic brakeforce distribution (EBD)
Hill-hold control (HHC)
Comfort soft braking (CST)
Hill descent control (HDC)
360-degree surround-view camera system
Two front object detection sensors
Four rear object detection sensors
Automatic vehicle hold (AVH)
Intelligent automatic high beam control (IHBC)
Adaptive cruise control (ACC)
Intelligent adaptive cruise control (ICC)
Intelligent speed limit control (ISLC)
Intelligent speed limit alert (ISA)
Traffic sign recognition (TSR)
Automatic emergency braking (AEB)
Forward collision warning (FCW)
Rear collision warning (RCW)
Lane departure prevention (LDP)
Lane departure warning (LDW)
Emergency lane keeping assist (ELKA)
Rear cross-traffic alert (RCTA)
Rear cross-traffic braking (RCTB)
Blind spot detection (BSD)
Door open warning for moving objects (DOW)
Front vehicle start reminder (FVSR)
Exterior Colors
Horizon White
Space Grey
Quantum Black
Interior Colors
Gray