2007 Infiniti M35 Gas Mileage

Let's talk about the 2007 Infiniti M35's gas mileage – a topic that's important to any owner, especially with fluctuating fuel prices. We'll dive into the factors affecting fuel economy, potential issues, and how you can improve your M35's MPG. This guide is geared towards intermediate car enthusiasts and DIY mechanics who want a deeper understanding beyond the sticker numbers.

Understanding the EPA Estimates and Real-World Numbers

The EPA (Environmental Protection Agency) provides estimated fuel economy figures for new vehicles. For the 2007 Infiniti M35, the EPA estimates typically ranged around 19 MPG city and 26 MPG highway for the rear-wheel-drive model. The all-wheel-drive (AWD) version usually saw slightly lower numbers. Keep in mind these are *estimates*, achieved under controlled lab conditions. Real-world MPG can vary significantly depending on several factors:

Driving Habits: Aggressive acceleration, hard braking, and high speeds drastically reduce fuel efficiency.
Traffic Conditions: Stop-and-go traffic consumes more fuel than consistent highway cruising.
Vehicle Maintenance: Neglecting maintenance, like tire pressure, oil changes, and air filter replacements, impacts MPG.
Environmental Factors: Weather conditions (cold weather reduces MPG), altitude, and terrain all play a role.
Fuel Quality: Using lower-octane fuel than recommended can negatively affect performance and fuel economy. While the M35 can *technically* run on 87 octane, premium (91 or higher) is recommended for optimal performance and fuel efficiency.
Vehicle Load: Carrying excessive weight in the vehicle reduces MPG.

Don't be surprised if your actual MPG differs from the EPA estimates. Many M35 owners report real-world figures closer to 16-18 MPG in the city and 23-25 MPG on the highway, especially with mixed driving and typical urban conditions. Factors like AWD and driving style can easily reduce these figures further.

The VQ35DE Engine and Fuel Efficiency

The 2007 M35 houses the venerable VQ35DE engine – a 3.5-liter V6 known for its smooth power delivery and relative reliability. While not the most fuel-efficient engine in its class, the VQ35DE offers a good balance of performance and reasonable MPG when properly maintained. Let's break down some key components related to fuel consumption:

Fuel Injection System

The M35 uses a multi-port fuel injection (MPFI) system. This system sprays fuel into each cylinder's intake port, rather than a single point in the intake manifold (like throttle body injection). This design allows for more precise fuel metering and better combustion, contributing to improved fuel efficiency compared to older injection technologies. However, components like the fuel injectors can become clogged over time, affecting spray patterns and leading to poor fuel atomization. This results in incomplete combustion and reduced MPG.

Symptoms of clogged fuel injectors include rough idling, hesitation during acceleration, and a noticeable decrease in fuel economy.

Oxygen Sensors (O2 Sensors)

O2 sensors are crucial for monitoring the exhaust gases and providing feedback to the engine control unit (ECU). The ECU uses this information to adjust the air-fuel mixture for optimal combustion. The M35 has multiple O2 sensors – typically two upstream (before the catalytic converters) and two downstream (after the catalytic converters). A faulty O2 sensor can send incorrect data to the ECU, leading to an imbalanced air-fuel mixture and reduced fuel economy.

There are two types of O2 sensors. The upstream O2 sensors are Air Fuel Ratio sensors, which provide much more precise and faster readings than the downstream O2 sensors. This is because they need to accurately monitor the air/fuel ratio to optimize performance and emissions. The downstream sensors primarily monitor the catalytic converter's efficiency.

A common symptom of a failing O2 sensor is a "Check Engine Light" with codes related to the air-fuel mixture or sensor performance.

Mass Airflow Sensor (MAF Sensor)

The MAF sensor measures the amount of air entering the engine. This information is another crucial input for the ECU to calculate the correct amount of fuel to inject. A dirty or failing MAF sensor can provide inaccurate readings, causing the ECU to inject too much or too little fuel. This leads to reduced fuel economy, poor performance, and potentially even engine damage.

Cleaning the MAF sensor periodically with a dedicated MAF sensor cleaner is a good preventative maintenance step. A faulty MAF sensor can also trigger the "Check Engine Light."

Catalytic Converters

While primarily emissions control devices, catalytic converters also indirectly affect fuel economy. A clogged or damaged catalytic converter restricts exhaust flow, putting extra strain on the engine and reducing its efficiency. This can lead to a noticeable drop in MPG.

Symptoms of a failing catalytic converter can include a rattling noise from underneath the car, a sulfur smell in the exhaust, and a significant decrease in performance and fuel economy.

Common Issues and Troubleshooting

Here are some specific issues that can affect the 2007 M35's fuel economy:

Vacuum Leaks: Vacuum leaks can disrupt the air-fuel mixture and lead to poor fuel economy and rough idling. Inspect vacuum hoses for cracks or leaks.
Spark Plugs: Worn or fouled spark plugs can result in incomplete combustion and reduced MPG. Replace spark plugs according to the manufacturer's recommended interval. Use the correct type and gap specified for the VQ35DE engine.
Tire Pressure: Underinflated tires increase rolling resistance, requiring the engine to work harder and consume more fuel. Check and maintain proper tire pressure regularly.
Wheel Alignment: Misalignment can cause excessive tire wear and increased rolling resistance, impacting fuel economy.
Dragging Brakes: A sticking brake caliper can cause the brake pads to constantly rub against the rotor, increasing rolling resistance and reducing MPG.

Troubleshooting Tips:

Start with the basics: Check tire pressure, fluid levels, and ensure proper maintenance is up-to-date.

Scan for Diagnostic Trouble Codes (DTCs): Use an OBD-II scanner to check for any error codes that might indicate a problem. A "Check Engine Light" is your first clue. Note the code and look it up for diagnostic information.

Monitor Fuel Trims: Long-term fuel trims (LTFT) and short-term fuel trims (STFT) can provide valuable insights into the engine's air-fuel mixture. High positive fuel trim values can indicate a lean condition (too much air, not enough fuel), while high negative values suggest a rich condition (too much fuel, not enough air). Analyzing these values can help pinpoint potential problems like vacuum leaks, faulty O2 sensors, or clogged fuel injectors.

Visually Inspect Components: Check for obvious signs of damage or wear, such as cracked hoses, leaking seals, or corroded wiring.

Improving Your M35's Gas Mileage

Here are some tips to improve your 2007 Infiniti M35's fuel economy:

Drive Conservatively: Avoid aggressive acceleration, hard braking, and high speeds. Anticipate traffic and maintain a steady speed.
Maintain Proper Tire Pressure: Check and inflate your tires to the recommended pressure (found on the door jamb sticker).
Keep Your Vehicle Properly Maintained: Follow the manufacturer's recommended maintenance schedule, including oil changes, air filter replacements, and spark plug replacements.
Reduce Weight: Remove unnecessary items from your vehicle to reduce weight.
Avoid Idling: Minimize idling time, as it wastes fuel.
Use Cruise Control: On the highway, use cruise control to maintain a constant speed and improve fuel efficiency.
Consider a Tune-Up: If your M35 has high mileage or is experiencing performance issues, a tune-up can help improve fuel economy. This might include replacing spark plugs, cleaning fuel injectors, and checking the ignition system.
Upgrade to Low Rolling Resistance Tires: Choosing tires specifically designed for low rolling resistance can marginally improve fuel economy.

While the 2007 Infiniti M35 isn't known for being the most fuel-efficient vehicle, understanding the factors that affect MPG and performing regular maintenance can help you maximize your fuel economy and keep your M35 running smoothly. Remember to prioritize preventative maintenance and address any issues promptly to avoid more costly repairs down the road. Good luck!