tried synthetic oil in an older workiing viehicle (1990) gmc 1 ton,350 engine. tried to save money on oil changes. did save, until i hade to put a new motor in it for 5000.00 k. if GM or any other company thought is was i good idea to put synthetic oil in your viehcle, they would do it from the factory. stick to dealer recommended oil changes or less. you can never change you oil too much, but you can definately change it not enought.