In my usage we like to keep passage number under 30. I know some have used up to passage of approximately 40 and still had decent results for some things. You state differentiation in your question but I am not completely sure what type or aspect of cell differentiation you are looking at.

The cell line was established long time ago, so I'm pretty sure that not even the seller knows how many duplication it has undergone (could be 1000 or 10 million). Also it is made from mushed mouse embryos, so the cells have stem-cell capabilities, and probably they can undergo an indefinite number of duplications. As Dr. Watson suggest above, the best way probably is simply to look at them and see if and their behavior start to be different (could be due to culture conditions or mycoplasma contamination). I made them differentiate into fibroblasts, adipocytes or endothelial structures, depending on the culture conditions and I never had any problem with the cell passage number. I'm sending you one of my paper for reference.

very thanks for your answer, Michael J Watson ·.in our lab we use it to test some natural compound if they can reduce fat accumulation. so that use for obesity therapy

also thanks for Danilo Zangani . your paper is very helpful for me.i'll read it clearly and if any question i'll contract you later.

As I know, the efficiency of differentiation in 3T3-L1 is significantly affected by the passage. You could read this paper "Protocol for effective differentiation of 3T3-L1 cells to adipocytes" from Zebisch (2012). In my experiment, I only used the passage below 10. If your differentiation protocol added something like "rosiglitazone", the differentiation efficiency would be ok. If not, I suggest you do not used too old cell in your experiment.