Hi. I added about half a litre of regular 5W30 engine oil to a 2000 Polaris Expedition 425 4x4. (engine & trans oil all in one). I just bought it with 422 miles on it & did not know it should only be synthetic. How big a deal is that & what is the oil change interval?

 

With it holding 5.5 quarts,don't think I'd worry about it,but to be honest with you if this machine is new to you and is the original oil and filter or it's been sitting up I'd change it.This machine has wet clutches so I wouldn't use synthetic car oil because of the modifiers in it that can cause clutches to slip. Dedicated oils out there that don't have friction modifiers in it such as Amsoil,Mobil 1,Valvoline atv oil,etc that you can use along with Polaris branded oil if you choose.Even the cheaper Rotella T6 5w40 is oil that many people use for cycles and atvs. Manual shows 100 hr interval on oil changes but that varies according to use.A lot of oil to change but I'd cut that down to at least 75 or even 50 hrs depending on use.0w40,5w30,5w40,5w50 you can use any of these weights with no problems.

 

My old Arctic Cats have a similar set up with wet clutches and transmission sharing the same oil. I used 0W40 Mobil 1 Euro Formula and even better Rosella 5W40 T6 . Neither have friction modifiers. I change at 500 miles and send a sample to Blackstone Labs. Always came back looking excellent.