Xulfiqar, you seem to be a very technical man and thank you for your suggestions. today i managed to go to mechanic and had the head bolts re-torqued. Two of the bolts got about 90 degrees rotation (one at the center of head and one at an end). Two others just gave a "tuck sound" and remaining two remained unchanged. Now lets hope the two bolts fix gives me relief.
And as far the intake pipe going to water body is concerned, i will get it checked but i want to ask you about the bypass pipe connected to tstat housing. This small pipe just comes out of the housing and connects back to radiator pipe. I assume that when tstat is installed and when engine is cold, this pipe bypasses the radiator and coolant circulates without passing through radiator. If i am rite then what will happen if i block this bypass pipe with a stopper?
sohna, i wish it was only a gauge fault but in fact gauge is not faulty. When the gauge goes up, i can feel the engine heat by feeling the pressure in radiator pipe. And also when the gauge goes to the upper limit, overflow tanks starts throwing out. This means that engine really gets hotter.
Thank you all for you precious comments/suggestion, specially xulfiqar.