overheating and/or mysteriouscoolant loss

[guyboy]

the saga continues.following a replacement cam belt and waterpump my overheating problem was cured for three weeks then return to exactly the same problem,i.e.no problems with temp unless i go above 60 then i boil up.
the reason i have brought this up is that my car is booked in for 3 days investigative work & i was wondering if anyone could point me in the right direction with regard to any causes & cures youve come across. any help to finally nail this problem ive put up with for 12k miles would be appreciated.

[spike]

Hi g maddox
Like you, i'm really struggling to understand why a cam belt and waterpump change would result in a temporary cure for the overheating. Good news it that a warped cyl head or damaged head gasket are very unlikely to be the cause as they would not fix themselves, even for 3 weeks. There is no mention of the removed pump being faulty (loose /damaged impeller, leaking seal etc) or that any debris was found in the cooling system during draining of the radiator etc - is this correct (i'm just looking for clues here)
Going back to basics, the engine could run hot for the following reasons -
Overfuelling, wrong fuel injection timing, charge air cooler radiator blocked, lack of lubrication or oil cooler fault. If it were any of these then the problem would be detected by the appropiate engine sensor and if severe enough,the engine would derate and log a fault code. I assume this has not happened so its back to the cooling system. Things to look for would be
Anything stopping airflow to the radiator core
Debris in the system or blocked tubes in the radiator
Faulty thermostat
Faulty water pump
System won't hold pressure when hot - hose leaks, faulty expansion tank pressure cap, water pump seal.

Sorry I can't be more positive.
Cheers Spike

[guyboy]

thanx for your response spike.i did ask the dealer re the removed water pump and apparently they could see nothing wrong with it,however,that does not rule out a possible fault with the new unit after 3 weeks.
The header tank seems to be very highly pressurized even ist thing in the morning when stone cold.i also need to top up the system by a pint or so most days even though it hasnt boiled up,but there is no visible signs of water leakage anywhere.stat & senser assy have not yet been changed.

[robin]

hi maddox
try changing the header cap as you could be loseing warter through it
or there could be air lock in warter system
drain all the warter out and refill with engin running and header cap off till the level settles then put cap on and see
if this helps.
why you drain the warter system you could put the garden hose in the top radiator hose with the bottom hose off this will flush out the radiator leave for about 10min or so then to flush the engin put the hose in the where the hose goes on to engin and let the garden hose flush out the engin for about the same time refill and give it a run

other poss could be the therostat sticking causing it heat up when going faster is yours a deisel as they run cold when not driven hard or fast

give it a try you got nothing to lose but a bit of time and it might cure it !!!

CHEERS

ROBIN