There is no inherent reason why synthetic motor oil would be bad for old cars. In fact, synthetic motor oils can offer a number of benefits for older vehicles, including improved performance, better protection against wear and tear, and longer service intervals.
That being said, it’s always important to consider the specific needs of your vehicle when choosing a motor oil. Some older vehicles may have seals or gaskets that are not compatible with synthetic oils, or they may have specific oil viscosity requirements that are not met by synthetic oils. In these cases, it may be necessary to use a different type of oil.
It’s also important to consult your car’s owner’s manual or consult with a mechanic to determine the best type of oil for your vehicle. They will be able to recommend the appropriate oil viscosity and type based on the specific needs of your vehicle.
Overall, synthetic motor oil can be a good option for older vehicles, but it’s important to carefully consider the specific needs of your vehicle before making a decision.