heating system playing up!!

my 95 p38 has some suspect heating. When i try and heat the cab, even on high speed fan setting, there is very little actual heat. However when i use the boost button, i get lots of heat for a few minutes, but have to turn it off, due to the noise. The other thing is that if i go around a major roundabout or corner, there is a sudden surge of warm air then back to luke warm.....does this mean there is an airlock in the system or is it the heating blend motors????

can you turn the systemto cold and does it go to cold? try both sides, if only one side is cold then its likely the blend motor on the opposite side(if that makes sense)

the turning and heat buisness suggests low water level in the heater, take off the pipes on the bulkhead that go trough to the heater(from engine side) and give the pipes a blast with a hosepipe, let it flow a bit to dislodge any crud. do the same to the other pipe then top ip yr coolant system, don't forget to use 50/50 water antifreeze mix when yr confident you've sorted it. the coolant requires 11 litres total so put a 5 litre antifreeze in! obviously you will have to let some water out!!!