What about changing back to regular oil from synthetic oil? What if you have been using ONLY synthetic oil since putchasing your Mustang brand new and then down the line after 36,000+ you want to change and to use ONLY regular oil? Can you do that without causing any damage to the engine and its internal parts? What's the advantage of changing over to regular oil from synthetic oil if you've been using synthetic oil for over 36,000+ miles since purchasing your Mustang brand new? I currently own a 36,200 mile 2002 V6 Mustang and I am trying to save some $$$DOLLARS$$$ and am thinking about using regular oil in my car. I have been using synthetic oil ever since I purchased my Mustang brand new though. Will it be okay to start using regular oil inside my V6's engine for the rest of the engine's life span? Or will I start having engine problems if I make the change from synthetic oil to regular oil? And what would be the answer if my car was a 4.6 liter GT Mustang? I also own a 2001 MUstang GT which has very low mileage (like 2,520 original miles) and I am thinking about changing over to regular oil for that car too. I have been using synthetic oil in my GT since I purchased it brand new. Will using regular oil cause any harm in my V6 or in my GT Mustangs if I have been using synthetic oil all this time since both Mustangs were purchased by me brand new? I'm hoping that I can do the changeover to regular oil if it's not going to do any harm to the engine and its internal parts. What do you think? Please explain.