Coasting in neutral is a technique used by some drivers of manual transmission vehicles to try to improve fuel economy. It involves shifting into neutral when going downhill or slowing down, rather than leaving the vehicle in gear. The idea is that with the transmission disengaged, the engine can idle rather than having to work against compression in the cylinders. This may seem like a reasonable idea for saving gas, but there are some important factors to consider before coasting in neutral in a manual transmission vehicle.
Is Coasting in Neutral Recommended for Fuel Economy?
In general, coasting in neutral is not recommended for improving fuel economy in modern manual transmission vehicles. Here are some key reasons why:
Loss of Engine Braking
When coasting in gear, the compression of the engine provides a braking effect that helps slow the vehicle down. This engine braking allows you to use the brakes less. But when you shift to neutral, this braking effect is lost. That means you’ll have to ride the brakes more to maintain your desired speed when going downhill. This puts added wear on the brakes.
Fuel Cutoff
In most modern fuel-injected vehicles, the engine computer will cut off fuel delivery when coasting in gear, as long as the engine speed is above the idle threshold (typically around 900-1200 RPM). This saves gas. However, fuel cutoff does not occur when coasting in neutral since the transmission is disengaged. So keeping it in gear allows more opportunities for fuel savings.
Restarting Engine Uses Extra Fuel
The fuel saved by an idling engine during coasting is usually canceled out by the extra fuel required to restart the engine when you need to speed back up. The fuel injection and ignition systems use extra fuel for getting the engine revving again. So any potential savings are lost from the restart.
Modest Impact
Several tests have shown the fuel economy differences are very modest between coasting in gear vs neutral. In normal driving conditions, any savings are in the 1-2 mpg range at best. For hypermiling enthusiasts trying to maximize mpg, this may be worthwhile. But for average drivers, the impact is small.
When is Coasting in Neutral Advised?
While coasting in neutral should generally be avoided for fuel economy, there are some situations where it may be recommended:
Long, Steep Descents
On very long, steep downhill sections, excessive engine braking can cause brake overheating or failure. In these cases, alternating between neutral and a driving gear may help manage speed while giving the brakes a rest. Follow the descent recommendations in your owner’s manual.
Tow/Haul Mode
Some new trucks and SUVs have a tow/haul mode that modifies transmission shift points and engine braking. When using this mode while towing or hauling, brief coasting in neutral may help control speed and assist the brakes. Check your vehicle guidelines.
Extreme Hypermiling
For hypermiling enthusiasts who are attempting record-breaking fuel economy, the slight gains from coasting in neutral may be worthwhile. But this should only be done in safe road conditions and not compromise normal brake usage. Use common sense.
Risks of Coasting in Neutral
While the fuel economy benefits are questionable, there are some definite risks associated with the practice:
Loss of Control
Coasting out of gear removes your ability to accelerate quickly to avoid hazards or complete maneuvers. This increases the risk of an accident in an emergency situation. Always keep the vehicle in gear when moving to maintain control.
Increased Wear
The transition from neutral to a driving gear causes extra wear on the transmission components. The synchronizers have to spin up the input shaft to match the transmission speed. Doing this repeatedly causes premature wear over time.
Forgetful Shifting
Many drivers forget to shift back into gear after coasting in neutral. This can be dangerous when you need to accelerate but have no power because you are still in neutral. Make a habit ofalways being in gear when moving.
Coasting Too Far
Because there is no engine braking when coasting in neutral, it’s easier to carry too much speed into corners or intersections. Go beyond your intended stopping point. This could result in running lights or dangerous maneuvers.
Unintended Movement
If you coast in neutral on an incline, the vehicle may roll unintentionally if the idle creep is insufficient to hold it. This could lead to a collision or other safety issue.
Best Practices
Here are some recommended practices for maximizing fuel efficiency in a manual transmission vehicle while avoiding the risks of excessive neutral coasting:
– Use gearing to maintain steady speeds without over-revving or lugging the engine. Match RPMs to road speed.
– Look ahead and time shifts to avoid unnecessary braking and acceleration. Coast in-gear when slowing down.
– Shift into neutral only when fully stopped. Avoid shifting into neutral when moving.
– Shift smoothly and deliberately, but don’t rush. Hard shifts waste fuel.
– Refer to your vehicle’s recommended shift points for optimal efficiency. Modern manuals have high top gears for cruising.
– Avoid excessive idling when stopped. Turn off the engine if stopped for more than 30-60 seconds.
– Maintain steady speeds and anticipate traffic flow to minimize acceleration and braking. The more constant the speed, the better the fuel efficiency.
Conclusion
Coasting out of gear in a manual transmission is generally not recommended as an efficient driving technique. The fuel savings, if any, are minimal. Much greater efficiencies can be gained through proper gear selection, steady speeds, and anticipating traffic. The risks of coasting in neutral also outweigh the questionable fuel savings. For optimal fuel efficiency and safety, remain in gear when moving and avoid excessive coasting in neutral. Focus instead on driving smoothly and predictably.
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Key Takeaways on Coasting in Neutral
– Not recommended for fuel savings due to minimal benefit
– Loss of engine braking can wear brakes faster
– Transmission wear from excessive shifts in/out of gear
– Risk of loss of control without ability to accelerate
– For maximal efficiency, use gearing properly and drive smoothly
Focus on smart driving techniques. Don’t prioritize coasting in neutral for fuel economy gains. Follow the recommendations in your vehicle owner’s manual for efficient operation. Drive defensively and maintain control of your vehicle at all times.