I rented my friend’s car and without thinking I filled the tank with diesel. Shortly afterward the car stopped working. The owner is demanding that I deal with the mechanic and continue to pay the rental fee until it is returned.

Q: Am I obligated to do all of that? Is there an exemption since I didn’t intend to damage the car?

A: In a circumstance in which a renter has no way of knowing that the car requires special fuel and consequently added the wrong fuel, he would be exempt. The owner must inform the renter of special circumstances and if he does not, the renter is exempt (according to some opinions this is the rationale for the exemption of meisah machmas melachah — see Shach 340:5).

In your circumstance the exemption does not apply since drivers know that ordinary cars do not take diesel fuel, and using it for an ordinary car is a negligent act for which one is liable.

If the owner has an insurance policy that covers this type of loss, the renter may not be liable for anything except what is not covered by the insurance. Although many authorities maintain that a mazik is liable for damaging insured items (Ohr Same’ach, Sechirus 7:1 and Maharsham 4:7), nevertheless, a rental agreement is different since it is understood that the renter will not be liable for damage that is covered by insurance (see Minchas Yitzchak 3:126), since it is assumed that insurance coverage is part of the agreement. Liability is limited to those costs that are not covered by insurance.

Regarding the owner’s claim that you should have to deal with the mechanic and continue to pay rent until the car is returned, it is not a valid claim. A mazik’s liability is limited to paying for repairs; it does not obligate the mazik to spend the time dealing with getting the damaged item repaired. The owner is the one who must invest that time (Shach 95:18 and Chazon Ish, B.K. 6:3).

Therefore, once the damage occurred, the owner may no longer charge rent while the car is being repaired since once the car is broken, the rental agreement is terminated. Although your negligence prevents the owner from earning rental fees on his car, he cannot compel you to reimburse him for that loss. Poskim debate whether one who leases a cow and damages it is liable for the time it cannot work.

Some authorities maintain that since the animal will heal, the only loss the owner suffers is the loss of income while the animal is healing and cannot work. Since there is no unemployment payment (sheves) for an animal the renter/mazik is not liable. Others disagree and contend that since animals are sold on a regular basis, wounding an animal so that it cannot work causes its value to diminish and the renter/mazik must pay for that loss (C.M. 307:6).

It is clear, however, that even the latter opinion (obligating the renter/mazik) agrees that he only pay for the animal’s diminished value due to its incapacity to work for a period of time, but does not have to continue paying the rental fee (see Nesivos 340:3 and Chazon Ish, B.K. 13:2-3).

However, it is appropriate to reach some sort of settlement to address your moral obligation since there are authorities who obligate, latzeis yedei Shamayim, one who, as a result of negligence, prevented another from earning a profit (Radvaz 1:84; Avnei Nezer, Y.D. 133; Imrei Yosher 1:149 and 2:33; cf. Beis Ephraim, C.M. 28; and Imrei Binah 1:8).