I have done B.TECH in mechanical engineering and presently working with an auto ancillary.i want to study further through correspondenc.

There are many options, and it all depends on your flair and interest. One of teh option shall be; Post Graduation in Engineering (Design, Thermo sciences, Production Technology, Industrial Engineering, Power Engineering, ...), followed by Doctoral or R&D work, and Subsequent Teaching and R&D Profes

There are many Institute that provide corresponding courses,you can go through mumbai university,IGNOU, Shivaji university and many more,it your choice for which field you want go for.