A floor jack should not be used to hold a car for any extended period. It is strictly a lifting device, not a support tool. The only safe way to work under a vehicle is to use dedicated jack stands. Relying on the jack alone is extremely dangerous due to the risk of mechanical failure or hydraulic fluid leaking past internal seals, causing a sudden collapse.
The integrity of a floor jack's hold depends heavily on its condition. A new, high-quality jack might maintain pressure for hours or even days, but an older model or one with worn seals could fail in minutes. Environmental factors like temperature shifts can also affect the hydraulic fluid, potentially leading to a slow leak and descent. The critical point is that this reliability is unpredictable. You have no warning before a failure occurs.
Here’s a comparison of how different support methods are rated for safety and duration:
| Support Method | Primary Function | Safe Duration for Support | Risk Level | Industry Standard Practice |
|---|
| Hydraulic Floor Jack | Lifting only | 0 minutes (Not Recommended) | Extremely High | Never use as sole support |
| Mechanical Scissor Jack | Emergency tire change | 0 minutes (Not Recommended) | Very High | For lifting only, not repairs |
| Quality Jack Stands | Supporting vehicle | Indefinitely (When properly placed) | Very Low | Mandatory for any work underneath |
| Vehicle's Own Tires | Chocked for prevention | Indefinitely (As secondary safety) | Low | Always chock wheels opposite the jack |
For absolute safety, follow this procedure: use the floor jack to lift the car, immediately place rated jack stands under the vehicle's reinforced lift points, and then slowly lower the car onto the stands. The jack can then be removed entirely, or left in place with minimal pressure as a secondary, but not primary, safety measure. Never trust your life to a hydraulic seal.
