I keep my cars for as long as possible unless something happens which requires me to sell them. Of course it's always better when they have been paid completely with no more monthly payments. Personally I don't think selling a car just because it's 4-5 years old is particularly wise(specially when you have just paid it off) as you take the brunt of the depreciation in the first 2 years of ownership. Whatever you save in monthly payments can always be set aside for maintenance rather than starting a new debt.