To do anything underneath a car, you have to Spiral Jack it up first. The process is pretty straightforward: Drive the car onto a hard and level surface, place a car jack under a suitable spot (individual jacking points can be found in your owner’s manual), lift the vehicle, place stands underneath and lower the weight of the vehicle onto the stands, removing the jack altogether. If this seems complicated, you may be wondering if you can just use the jack to keep it up? No! Maybe there is one exception … but let’s review the basics first.

There are two main kinds of jacks: mechanical (like the scissor jack you may have stored with your spare tire) and hydraulic (a floor or trolley jack).

Most modern mechanical jacks use a manually turned screw that threads through two sides of a flat diamond-shaped frame, bringing the outside ends closer together to lift the load. Hydraulic jacks use two cylinders connected by hydraulic fluid to convert some force on the operator’s side (amplified even further by a lever) to produce major lifting power.
Risks

A scissor jack is more dependable on uneven ground or gravel — hence the inclusion in your spare kit — but it’s not meant to hold weight long term. Hydraulic jacks are designed with internal seals to keep the fluid from flowing back into the chamber and lowering the load, but seals can rupture or take on small leaks that will gradually lower the jack if there’s a load on it.

If you need to lift the vehicle to do work underneath it, you must properly place jack stands and let them carry the brunt of the load. Not only do you risk mechanical or hydraulic failure by only relying on a jack, you also create a potentially unbalanced, very heavy load by only jacking up one point. Leaving a vehicle on only a jack for any amount of time unattended means anyone could come over and accidentally drop the whole thing. Can You Use a Floor Transmission Jack Without Stands?