2018 BMW i3s (94Ah) with Range Extender Maintenance Schedule & Service Intervals

Key Takeaways

• The 2018 BMW i3s (94Ah) with Range Extender combines a sport-tuned electric powertrain with the same 0.6L two-cylinder range extender engine used in the standard i3 REx, which requires periodic oil and filter changes.
• Engine oil and filter changes are determined by BMW's Condition Based Service (CBS) system; the engine uses approximately 2.6 liters of 5W-30 or 5W-40 synthetic oil, with a typical 12-month or 10,000-mile interval.
• Brake fluid must be replaced every 2 years using DOT4 specification fluid.
• Spark plugs and engine air filter are officially long-term rated and do not require periodic replacement under normal operating conditions.
• BMW Ultimate Care covers scheduled maintenance for the first 3 years or 36,000 miles, with a basic and powertrain warranty of 4 years or 50,000 miles.
• The REx engine performs an automatic self-maintenance cycle if unused for extended periods, typically running when the battery is below approximately 75-80% charge to lubricate components.

Understanding the 2018 BMW i3s (94Ah) with Range Extender

The 2018 BMW i3s represents the "sport" variant of the i3 lineup, offering increased power output (from 170 to 181 hp) and torque (from 184 to 199 lb-ft), a lowered sport suspension, and wider tires. The i3s is approximately 20 kg (44 lb) heavier than the standard i3, at 1,460 kg with the range extender. The 94Ah REx variant is paired with the same 0.6L two-cylinder engine derived from a BMW scooter.

The exterior was refreshed for the 2018 model year, with a new front bumper, horizontal turnsignal light openings, standard LED headlights, and a revised rear bumper. The i3s features blacked-out chrome accents compared to the regular i3.

BMW Factory Warranty and Maintenance Program

The 2018 BMW i3s with Range Extender was sold with comprehensive factory coverage:

Engine Oil and Filter Change

Factory Schedule

The range extender engine requires oil and filter changes at intervals determined by the CBS system. The engine uses approximately 2.6 liters of oil for a service fill, with a typical 12-month interval recommended (though some references note up to 24 months depending on driving conditions).

Oil Specifications:

• Capacity: Approximately 2.6 liters
• Recommended Oil: 5W-30 or 5W-40 synthetic oil meeting BMW specifications
• Filter: Replace with every oil change

Owner Guidance

Given the extended periods between REx engine use, many owners recommend an annual oil change as a conservative measure. Some forum discussion notes that the REx engine's oil remains very clean on a 2-year schedule due to limited use as a generator rather than a propulsion engine.

Service Costs: A BMW i3 service (including oil change) typically costs between £127 and £356 depending on the service type (interim, full, or major).

Spark Plugs and Engine Air Filter

BMW's official documentation confirms that "due to the light duty and relatively constant operating speeds, the range extender engine's spark plugs and air filter are long-term rated, which do not need periodic replacement."

Parts Information:

• Spark Plug Part Number: NGK LMAR8AI-8E (BMW Part No. 12 12 2 357 197)
• Quantity: 2 spark plugs
• Ignition Coil Part Number: 12 13 8 569 194

Owner Guidance: While spark plugs are not a scheduled maintenance item, some owners may choose to replace them if experiencing drivetrain errors or misfire codes. The spark plugs and coils are accessible for inspection if needed.

Brake Fluid Replacement

BMW requires brake fluid replacement every 2 years for the i3, including the REx variant. The brake fluid must meet DOT4 low-viscosity specification.

Owner Guidance: Brake fluid is hygroscopic, absorbing moisture from the air over time, which can cause corrosion within the braking system and degrade brake pedal feel. The 2-year interval is a conservative safety standard to ensure braking system integrity.

REx Maintenance Cycle

The range extender engine automatically performs a self-maintenance cycle if it has not been used for an extended period. This cycle typically runs when the battery is below approximately 75-80% charge. During this cycle, the REx engine runs for several minutes to lubricate internal components and ensure proper operation. This is a normal function and does not require user intervention.

Owner Guidance: If the REx is rarely used, running it for 10-20 minutes weekly or at least monthly is recommended by many owners to maintain fuel system health and prevent injector clogging. Using a high-quality premium fuel with detergent additives can also help prevent injector issues.

Oxygen Sensor and Other Service Items

Oxygen Sensor

BMW specifies oxygen sensor replacement at 150,000 miles. The oxygen sensor deteriorates strictly on a mileage basis and must therefore be replaced to maximize vehicle fuel economy and minimize exhaust pollution.

Cabin Air Filter

The cabin air microfilter is typically replaced during service visits. The CBS system may indicate when replacement is due.

Coolant

There is no prescribed coolant change interval in BMW's official documentation for the i3 REx. Coolant should be inspected during regular service visits.

Summary Maintenance Schedule