Thread: TDI Coolant Flush

Normally coolant runs from the engine through the thermostat and into the radiator where it's cooled and is fed back into the engine at the bottom and around again for another lap and so on.

The go is to 'reverse flush' the cooling system so what you do is run water backwards through the cooling system.

To achieve this what you do is run water into the thermostat housing back through the block (top to bottom) and back up through the radiator (bottom to top) and then out onto the ground. An old piece of radiator hose is often useful here to direct the flow down and away from the engine compartment. The engine is not running whilst doing this.

The usual process to flush a cooling system is as follows.

1/. Remove thermostat (very important)

2/. Turn heater 'tap' on

3/. Disconnect top hose at either radiator or thermostat housing.

4/. Connect garden hose and away you go.

What the pros do is run an air feed into where the water enters the thermostat housing and when the water is flowing well give a blast of compressed air into the system. This gives a bit more 'oomph' into the flushing process but needs to be done carefully. Overdoing the air could damage the cooling system components ( especially in an older weaker system) and needs to be done sensibly.

When done fit a new thermostat, not a cheap crappy one, use a quality OEM / LR one, not some tridon etc POS and make sure it's of the correct temperature bypass or non-bypass type. If you don't know the difference the new one should look the same as the old one. Non bypass thermostats are shorter than bypass types, don't rely on the children at Repco / Supercheap to know the difference as they are generally clueless when it comes to this.



The thermostat on the left is a bypass thermostat from my Tdi 300 the thermostat on the right is a Holden non bypass thermostat.

Refill the cooling system with your favourite coolant / inhibitor and bleed accordingly and 'Bob's your uncle' .

Deano