My Clubman has a six-speed manual transmission. Is it bad to coast downhills in neutral? I know it is an ignorant question, but my Honda motorcycle manual says not to do this for transmission lubrication reasons. So I'm wondering if the same thing is true for my Cooper Mini?

 

Whether its bad for the transmission or not, there really is no benefit to coasting in neutral. If you leave the car in gear and take your foot off the accelerator pedal, fuel consumption goes to zero.

 

I (respectfully) disagree with this, in practice anyway. When I take my foot off the gas in gear, the car starts slowing down regardless of which gear I'm in. So in practice, I have to keep my foot on the accelerator to some extent to maintain my speed. In neutral, however, the car coasts freely without the transmission drag. Which brings me back to the original question: Is that hard on the transmission or some other part of the powertrain?

 

I believe what Nik is saying is that when coasting in neutral, the engine is idling and using fuel. In contrast, when coasting in gear, the DME cuts off the fuel injectors because no fuel is required.

 

^ This.

Also, the only time I could see anyone coasting in neutral would be on the highway. Just use cruise control in this case, and let the ECU monitor speed and fuel.

Again, I see no benefit to what you want to do.

 

Here's an AI response to your question:

Coasting downhill in neutral will not cause significant mechanical damage to the manual transmission itself, as the internal components are adequately lubricated by splash-style oiling. However, it is a poor and unsafe driving practice due to the potential for other, more serious, issues.

The primary concerns with coasting in neutral are:

Reduced Vehicle Control and Safety Risks: Coasting eliminates engine braking, which means you must rely solely on your service brakes to control speed. On long or steep hills, this can cause the brakes to overheat and experience "brake fade," leading to a dangerous loss of stopping power. Being in neutral also prevents immediate acceleration if needed in an emergency.

Increased Brake Wear: Because you lose the natural slowing effect of the engine, your brake pads and discs will wear out much faster due to increased use and heat buildup.

Reduced Fuel Efficiency (in modern cars): Modern fuel-injected engines, like those in the Mini Cooper R56, cut fuel supply to the engine completely when coasting downhill in gear with your foot off the accelerator (deceleration fuel cut-off). In neutral, the engine must idle to stay running, which consumes a small amount of fuel, making it less fuel-efficient than staying in gear.

Potential Clutch/Synchro Wear (when re-engaging gear): While the transmission is fine in neutral, re-engaging a gear while moving at speed requires careful rev-matching. A failure to do this properly will cause wear on the clutch and the transmission's synchros.
Legality: In some jurisdictions, coasting in neutral is considered illegal as it is seen as a loss of vehicle control.

For safe and efficient driving, it is recommended to keep the car in an appropriate low gear when descending a hill and use the engine braking to help control your speed, reserving your brakes for actual slowing or stopping.

 

i've never heard of it being bad to coast in neutral. that said, i don't have any references i could cite. however, i've never avoided doing what you're saying. in various traffic situations, i might coast a little bit in neutral. i just don't see how it would cause a negative result.