Is coasting in neutral gear possible with a manual transmission?
4 Answers
Manual transmission vehicles should not coast in neutral gear. Whether it's a manual or automatic transmission car, coasting in neutral is not recommended as it can cause impact to the transmission and compromise driving safety. Therefore, drivers are advised to break the habit of coasting in neutral during regular driving. For automatic transmissions, shifting into neutral while coasting reduces oil pressure inside the transmission, affecting lubrication and heat dissipation. Prolonged or long-distance coasting in neutral may potentially lead to automatic transmission failure. As for manual transmissions, coasting in neutral subjects the transmission to significant impact forces, which can reduce its service life.
I regretted trying coasting in neutral with a manual transmission a few times. Last time when going downhill on a mountain road, I shifted to neutral to save fuel, but the brakes became increasingly soft until the brake warning light on the dashboard came on. Later, I learned it was because the vacuum booster pump didn't have enough pressure when the engine was disconnected from the drivetrain. Thinking back now, it's scary - if a car had suddenly appeared in front, I wouldn't have been able to stop in time. Moreover, modern fuel-injected cars cut off fuel supply when coasting in gear, while they actually consume more fuel maintaining idle speed when in neutral. My mechanic friend also mentioned that automatic transmission manuals explicitly prohibit coasting in neutral, and the same applies to manual transmissions. From a safety perspective, it's really not worth risking for minor fuel savings - coasting in gear is the most reliable approach.
I've seen friends' transmissions needing major repairs due to long-term coasting in neutral. When the engine and transmission are separated, the intermediate shaft bearings rely entirely on gear oil splash lubrication. If the coasting time is too long, the oil film can't hold up. Especially on downhill sections, gravitational acceleration causes the RPM to skyrocket, and the dry friction of bearings can reach temperatures over 100 degrees Celsius. Our auto repair shop has handled several cases of sintered synchronizers, and upon disassembly, all showed blue overheating marks. There are even more dangerous scenarios - coasting in neutral during emergencies makes it impossible to downshift and rev-match in time, resulting in countless rear-end collisions. When coasting in gear, the engine can still assist with deceleration.
During driving tests, the most frequent yelling from instructors was about prohibiting coasting in neutral. Now I understand this is a life-saving skill: engine braking in gear helps stabilize speed, especially preventing skids in rain or snow. Coasting in neutral increases braking distance by at least 30%, particularly when fully loaded or going downhill. With the driveshaft disengaged, all braking pressure falls entirely on the brake pads - overheating and failure of the wheel cylinders is no joke. Driving tests mandate instant failure if coasting in neutral exceeds 5 seconds, and you'll get penalty points if caught on road cameras. For real fuel savings, it's better to anticipate road conditions and coast in gear by releasing the throttle - fuel injectors shut off in modern fuel-injected cars, making this method actually more economical.
