Is one allowed to sit on a car bonnet on Shabbos, as the person will weigh the car down, but not move it out of its place? Is it worse if one were to raise oneself onto the bonnet by hand?
It is permitted to sit on the bonnet (hood) of a car Shabbos, even tough the car will sink slightly. The reason is because a car is considered a kli shemilatchto lissur and it is permitted to use it for a permitted use. This is privided that sitting onthe car will not activate any alarm system…
Shmiras Shabbos khilchoso 20-77, Tiltulei Shabbos Responsa from R’ Moshe Feinstein zt”l 7.