Ropey engine performance

Re My YR 2000 4.0 V8 petrol.

Amongst numerous other jobs i managed to gets done over the weekend i replaced the heater matrix o rings and have now managed to stop the coolant loss into the drivers footwell.A few days later the temp gauge went to max and the red light came on, i stopped immediately and allowed it to cool, fortuantely i was not too far from home and gingerly got the car home. Investigation showed that i had an self inflicted air lock, managed to remove air lock,topped up system and now temp gauge stay around middle and heater work fine.

Engine now sounds a bit ropey and the acceleration is not what is used to be - almost if if it has a slight hesitation and feel a bit sluggish. I have also noted that in addition to the V8 purrrrrr it has developed a "puffing" noise - in it overheating could i have screwed the head gasket? or do you think that i have leak in or around the exhaust manifold?

Is there anyway that i could test to see if the head gasket is gone or if it is exhaust manifoild ?

Any ideas help would be greatfully received.

Do a compression test first. Are you loosing water?

Hi, i will take your advice and get a compression test done -what results am i lookinmg for for and what will it indicate if i getr some thing different?

Ref your question - no my water level seems to be constant - when hot the level drops approx 1/2 inch and when cold it is spot on the mark