Help  required

Iv An A4 2005 1.9tdi, over the last number of months my heater only works whenever it wants, now am loosing the coolant out the resovour, system pressure checked for leaks, all good, new water pump, thermostat ,radiator and alternator fitted  over the last months, tried bleeding air out the system, no blockages as iv ran water hose through the system via the internal heater hose back out the resovour, any advice would be much appreciated, thanks

Hi William....welcome to the Forum

I can only think it is one of two things...

1. Pressure cap is defective, not holding pressure and letting air in and pressure out to allow the boiling point to be too low, hence losing coolant out of the reservoir.

2. Air lock somewhere up by the matrix. I used to have a tool when I owned a garage which vacuumed down the entire cooling system and then purged it with coolant under pressure, was sometimes the only way to get the bl**dy air out of the cooling system.

Sometimes, it won't necessarily leak coolant but you can be introducing air into the system via poor sealing joints or defective cap...worth checking before condemning head gasket, etc

Let us know how you get on with finding the fault

Cheers    Trevor

Hi Trevor 

I can't see it being the cap as every time I open it there's loads of pressure behind it, underneath the reservoir you can see the staining of the water on the body, will have to check to see if garage have something like you say to blow out the air under pressure, it's a pain in the a....

cheers and thanks again