Should grandpa pay back the money he spent on buying a car for his grandson?

It should be returned. The old man has worked hard all his life, and his old age is to enjoy life. More importantly, it must be guaranteed. Unless he has enough savings, he can buy other things, and then the younger generation will decide whether to accept the gift from the old man. Grandpa should pay back the money for his grandson to buy a car. It is not whether he should buy a car or other things for his grandson, but whether he has economic conditions first. If the elderly can't even guarantee the basic life, they have no obligation to buy it.