I change it when it gets too dark and thick.
but I hate frying things with new oil..just isn't the same. You can strain out anything in the oil and use it for quite awhile. I know there are place sthat have grease from many years ago they just keep straining it and adding new.
should you change the oil in the deep fryer?
Really? Wow I love it when I change the oil in the fryer everything seems so much more crip and tastier
I change the oil normally after 3 or 4 fry times. But if I fry a lot of something (chicken, lumpia, etc...) or any type of seafood I change it after that fry.