Toyota tacoma oil type

Changing oil in tacoma today, I’m not sure if conventional oil or full synthetic oil was used during last oil change. If i put Full synthetic oil in the truck while conventional oil or synthetic blend was used last, will this cause damage or more wear on the engine?

Also doing diff fluid and wondering if i need new crush washers in order to do it.

On another note I plan on topping off coolant, If the previous owner put concentrate with water in, If i top off with 50/50 mix will it cause damage or increase corrosion?

Sorry for the influx of questions just curious and don’t want to do anything the wrong way. Thanks!

 

No
Yes
No

 

Synthetic all the way!!!
Hard tacom gave you all the great answers