Hi.

Having a coolant issue on a 2001 1.9 TDi AJM engine.


Symptoms are;

No leaks. No loss of coolant. No white smoke. No yoghurt under cap. No oil in water.

No heat from heater, and although with only water and no coolant, never overheats at idle or casual driving, starts to overheat when driven fast (haven't seen how hot it will go as stopped at around 120).
Flushed heater core, yet no water seems to circulate. Outlet hose remains cold.

Have flushed the matrix, radiator and block, installed new thermostat (even though the old one tested fine).
From the stat hole, I can see the black plastic vanes of the impeller (not broken nor slipping) and also the pump spinning with the engine turning.
When cold there is no return to the expansion tank although when warm it does return.

Yesterday, filled it with distilled water and because I could only add 3 or 4 litres, did my best to bleed it, then took it for a fast run and once it was hot, all the water disappeared from the expansion tank. Once refilled, the expansion return hose was working properly, which made me wonder if the problem is not trapped air?

Was planning to fill with proper G12/water mix today and see if it still overheats?


So, are these pumps known to part fail? Or to weaken?
Could the matrix still be blocked or have trapped air?
Where else could there be a blockage?


Previous owner had mixed coolant types.


Any help or ideas would be greatly appreciated.

Thanks in advance.