Gunk high mileage motor flush safe?

Answer 1

Well in theory all it should be is concentrated detergents. That being said, you shouldn't keep it in the motor for any extended length of time, also, don't use it as an additive to motor oil. Throw it in, take it out! If anything does fail, its not going to be because Gunk is so powerful it ate your gaskets. Your gaskets were old and bound to fail. If your that concerned, you should be looking to the junkyards for a newish-er block and save your money.