xinghoh, does your temperature shoots to the sky? it does happen to me recently and it turned out to be the water pump. usually, if this is the case, if u look at the bottom of the car from the front (below spoiler, underneath the engine), u cant see anything happening if u switch off the engine.
fill up the radiator (wait till it cools down a bit) untill full and start up the engine, then look again underneath. if u can see water dripping quite fast, then most probably its the water pump. if you are fast and workshop is near, you might be able to make it there in time, but be sure to bring 2 - 3 bottles of spare water and watch the temperature gauge closely all the way. stop the car and kill the engine immediately if the rises above halfway.
the original water pump from proton parts center glenmarie is around RM 400 + -, and installation is around 100 - 150. u should get a one year warranty if u install it at authorised proton workshop.
btw, you should be using metal gasket as compression is now much higher than before. make sure to also seal the head with liquid gasket before attaching it back to the engine block. a good mech will also check your timing belt and all the beltings and pulleys along installing the new water pump.
is your pistons, conrods and all related hardware inside still stock?
what's the boost reading like?
and what ecu is the car using - mmc or siemens?
you better get it dynoed to see clearly what's happening between air and fuel ratio. anyway u can say that it is guzzling more fuel by checking the spark plugs, but still this will not indicate correctly and precisely what's actually happening.
if your car is using mmc ecu, then they might suggest a piggyback unit such as eManage (GReddy) or if you have the budget, go for the better ones (HKS, vManage...etc) which have better/wider range of tuning for better future mods...
for siemens - from what i heard, u cant really do anything cheap (GReddy should cost you around RM1k - including installation, remap and dyno - i did mine at N1 Racing sunway last time..), unless u changing the whole management system, as any piggyback / standalone cannot re - write the current ecu settings. it will go back to standard settings no matter what you try. kalau diorang tipu, aku pun tipu laa...coz i dont have any experience with siemens...
guys, please correct me if i'm wrong..:)