So theres my question , ive seen alot of threads with that in it but everybody got there opinion .
i was told that toyota coolant was the only thing i should put in my is250, wich i did but when they replace my alternator they removed a hose and lost a little of coolant , he top it off with some prestone so is it bad or not ?

weirdly im pretty sure my heat on driver side stopped at the same time or almost but im not 100% sure .he didnt put alot of prestone but still ,im wondering

 

Losing heat on the driver side is very likely a function of having air trapped in the cooling system, rather than due to the mixing of the two coolants. I would personally try to stick with the Toyota coolant, but I'm sure a small amount of prestone isn't going to hurt anything.

The air in the system could lead to issues with overheating though - if I were you I would go through the process of burping the system to remove any air, and see if that fixes the heat problem you are experiencing.

 

^Agreed! Remove that trapped air. It can cause much worse things that just the heat not working. Do not worry about the little bit of Prestone; but do only use Toyota coolant in the future. It contains Toyota-specific additives that extend the life of the hoses and the cooling system in general.