Minor Negative Impacts (occasional revving):
* Wear and tear: While not significant with a few revs, it does increase wear on engine components, especially the valve train and piston rings. Think of it like repeatedly slamming your brakes – it's not disastrous once or twice, but constantly doing it leads to premature wear.
* Fuel consumption: You're burning fuel without moving, which is inefficient.
* Emissions: Increased engine speed means increased emissions.
Significant Negative Impacts (frequent or high-RPM revving):
* Increased wear and tear: This is amplified. High RPMs for extended periods put significant stress on engine components, potentially leading to premature failure.
* Damage to engine components: Over-revving can cause serious damage to internal engine parts, including bent connecting rods, broken pistons, or damaged crankshaft bearings.
* Catalyst damage (catalytic converter): High RPMs can overheat the catalytic converter, leading to failure.
* Waste of fuel: This becomes a much larger problem.
* Noise pollution: Annoying and potentially disruptive to your neighbors or environment.
When it *might* be acceptable (rare and specific situations):
* Checking engine response: A quick rev to check for rough idling or other performance issues can be acceptable, but should be brief.
* Warming up a carbureted engine (older vehicles): Carbureted engines sometimes benefit from a brief period of higher RPMs when cold, but this practice is less relevant with modern fuel-injected engines. Even then, a gentle warm-up is better than revving.
In short: Avoid revving your engine in neutral unless absolutely necessary and keep it brief and at reasonable RPMs. The benefits are negligible, and the potential downsides outweigh any perceived positives. Consistent idling is more than sufficient to warm up a modern engine.
