I use Fuel Power in my Golf TDI as per Terry's advice. It has a 55L tank but I regularily fill up with 60L (15.8 gal). Diesel quality isn't the greatest here, so is it OK to use 4 ounces per tank instead of the recommended 3 ounces (1 ounce per 5gal)? Does it do anything or am I just wasting the additive?