A car can typically idle for 24 to 48 hours on a full tank of gas before stalling, but it's a terrible idea for your engine and is illegal in many places due to emissions laws. The exact time depends heavily on your vehicle's fuel tank size and engine efficiency. For instance, a large SUV with a 25-gallon tank will idle much longer than a compact car with a 12-gallon tank.
Letting your car run stationary for extended periods, known as idling, causes significant engine wear. Because the engine isn't operating at its optimal temperature, fuel combustion is incomplete. This leads to fuel residue building up on spark plugs and cylinder heads, and water condensation can accumulate in the exhaust system, speeding up corrosion. Modern cars with extensive electronics can also strain the alternator at low RPMs.
Safety is another major concern. Prolonged idling in an enclosed space can lead to a fatal buildup of carbon monoxide gas, which is odorless and colorless. Many municipalities have anti-idling ordinances with fines to reduce pollution and protect public health.
The following table provides estimates for different vehicle types under ideal conditions:
| Vehicle Type | Approximate Idling Time on a Full Tank | Key Factors |
|---|
| Compact Sedan (e.g., Honda Civic) | 18 - 30 hours | Smaller fuel tank (12-13 gal), efficient 4-cylinder engine. |
| Full-Size SUV (e.g., Chevrolet Tahoe) | 30 - 50 hours | Large fuel tank (24-28 gal), but less efficient V8 engine. |
| Half-Ton Pickup Truck | 24 - 40 hours | Similar to large SUVs, depends on engine size and tank capacity. |
| Hybrid Vehicle | Can exceed 50+ hours (with cycles) | Gas engine frequently shuts off, dramatically conserving fuel. |
Ultimately, aside from brief warming up in cold weather (which modern engines don't need), there's no good reason to idle for more than a few minutes. You're wasting fuel, harming the engine, and polluting the air.
