As per your need, I am giving you list of the colleges in Coimbatore with contact address that offering the diploma in mechanical engineering course.

C.I.T. Sandwich Polytechnic College
Avinashi Road, Civil Aerodrome
Coimbatore, Tamil Nadu
(0422) 2573034, 2574071, 2574072
(0422) 2573374

Christ The King Polytechnic College
Othakkalmandapam
Coimbatore, Tamil Nadu
(0422) 2610366, 2610177, 26550977
(0422) 2610366

G.R.G. Polytechnic College
Kuppepalayam, S.S. Kulam (PO)
Coimbatore, Tamil Nadu
(0422) 2929090, 2929091
7708079911
(0422) 2654323

Government Polytechnic College
Avinashi Road, Civil Aerodrome Post
Coimbatore, Tamil Nadu
(0422) 2573218, 2595218, 2573218
9894257059

Government Polytechnic College for Women
Bharathiyar Road, Siddhapudur
Coimbatore, Tamil Nadu
(0422) 2240917, 2210919
9443374970

Hindusthan Polytechnic College
Behind Nava India, Avinashi Road
Coimbatore, Tamil Nadu
(0422) 4440555
9894133333, 9843273344
(0422) 2561655

Jeeva's Polytechnic College
383/1, Mayleripalayam Village, Othakkal Mandapam, Arisipalayam (Post), Valzhukuparai Road
Coimbatore, Tamil Nadu
(0422) 2638555, 2638777, 2638667
(0422) 2638672

K.M.G. Polytechnic College
Valparai Main Road, Angalakurichi Post, Pollachi
Coimbatore, Tamil Nadu
(04259) 286530, 287207, 287090

Karpagam Polytechnic College
Pollachi Main Road, Eachanari
Coimbatore, Tamil Nadu
(0422) 2611082, 2611146, 2611479

Nachimuthu Polytechnic College
Udumalai Road, Pollachi
Coimbatore, Tamil Nadu
(04259) 236030, 236040, 236050

Nanjappa Polytechnic College
Karumathampatti
Coimbatore, Tamil Nadu
(0421) 2332669, 2335347
9944936130
(0421) 2335348

Nanjiah Lingammal Polytechnic College
Sirumugai Road, Mettupalayam
Coimbatore, Tamil Nadu
(04254) 222242, 223008

P.A. Polytechnic College (PAPC)
Palladam Road, Pollachi
Coimbatore, Tamil Nadu
(04259) 221385
(04259) 230892

P.S.G. Polytechnic College
Po.1611, Peelamedu
Coimbatore, Tamil Nadu
(0422) 2572177, 2572477, 2580455, 2578455, 4344777
(0422) 2573833

R.V.S. Polytechnic College
Kumaran Kottom, Kannampalayam, Sulur
Coimbatore, Tamil Nadu
(0422) 2681123, 2681124
9994897333
(0422) 2680047

Ranganathan Polytechnic College
REC Kalvi Nagar, Viraliyur Post
Coimbatore, Tamil Nadu
(0422) 2619170, 2619172
9750381073, 9789564654, 9500981235

Sankara Polytechnic College
Saravanampatty
Coimbatore, Tamil Nadu
(0422) 2666490, 4313555

Sree Narayana Guru Polytechnic College (S.N.G.P.C.)
95, Sree Narayana Guru Road, Saibaba Colony
Coimbatore, Tamil Nadu
(0422) 2447805
9443143876
(0422) 2440234

Sri Ramakrishna Mission Vidyalaya Polytechnic College
Sri Ramakrishna Vidyalaya (P.O), Periyanaickenpalayam
Coimbatore, Tamil Nadu
(0422) 2692432

Sri Ramakrishna Polytechnic College
Vattamalaipalayam, NGGO Colony Post
Coimbatore, Tamil Nadu
(0422) 2461349
(0422) 2460396

Sri Ranganathar Institute of Polytechnic College
1/104-A, Athipalayam, Kovil Palayam to Thudiyalur Road, Coimbatore North
Coimbatore, Tamil Nadu
(0422) 2904008, 2904009

St. Joseph Polytechnic College
Velanthavalam Road, Pichanoor Village, Veerappanur
Coimbatore, Tamil Nadu
(0422) 2656577, 2656599
9442632080
(0422) 2656533

Suguna Polytechnic College
Nehrunagar, Kalapatty Road, Civil Aerodrome P.O.
Coimbatore, Tamil Nadu
(0422) 2627503 , 2627708
(0422) 4555555

Thiruvalluvar Polytechnic College
No.6, Vellamadai Village, Athipalayam
Coimbatore, Tamil Nadu
(0422) 2903450
9095133312

V.L.B. Janaki Ammal Polytechnic College
Arivoli Nagar, Kovai Pudu
Coimbatore, Tamil Nadu
(0422) 2807652
(0422) 2807552