@Xulfiqar:
Thanks for the explanation on the function of the resonator plenum tube, that makes a lot of sense..
So you think these two pipes could've been the culprit here? They were full of rust from inside and practically choked..
I did have all of the pipes replaced recently.. and one pipe which was previously metal, had corroded and was leaking, so the mechanic put in another pipe in place of it.. Here are pics of the old pipe:
Is it possible that in changing the pipes, he may have disturbed the height of the pipes in some way and that's causing the problem?
I will search carefully for the leaks also.. Any tips on checking and fixing leaks? I once saw an additive which you can add to the cooling system and would seal any leaks, is it a good idea for such cases?
And also, how can I set a bleeding nipple so I can purge the air when filling the coolant, is it also a good idea to have the car inclined while filling the coolant so as to facilitate the natural passing out of air?