Recently bought a VRS and previous owner mentioned it just had new oil cooler fitted as old one failed and recommended me to do a coolant flush as the coolant inside expansion tank was black.

 

Tested the car and everything worked fine, no leaks, no overheating, heaters working perfect etc.

 

Now few days later I've just done a coolant flush and my heaters no longer blow hot air.

 

I drained the radiator, added distilled water to max, started car then added more water until max and then added radiator flush. Let the car idle with cap off for 30 mins with heaters on full, no hot air blowing, temp reached to 90 and still no hot air and expansion tank not bubbling/boiling etc. Put cap back on and went for 10 min drive, still no hot air from heater and temp still at 90 so no overheating issue here. Parked the car to let it cool down for an hour then drained the radiator and added fresh coolant. Let car idle with cap off for 30 mins with heaters on. Still no hot air coming through and car reached correct temp at 90. 

 

Now have driven the car for a couple miles and temp doesn't go above 90 so I assume this means it doesn't overheat and there is no airlock in system? 

 

The car fully warms up in 10-15 mins so I assume thermostat is working fine. 

 

Just can't figure out why my heaters don't blow hot air anymore. Was fine before so I don't know what's gone wrong.

 

Can anyone help please, thanks

Well either the matrix is completely blocked by sludge from the flush, or airlocked, or the temperature flap motor in the cabin isn't routing air through the matrix when heating is requested.

 

With engine running, try turning the heater setting from max cold to max hot several times to see if that makes any difference; that will demand movement from extreme to extreme positions of the temperature airflap.

Could do with getting a VCDS scan of the HVAC module to see if there are any V68 motor faults logged (that's the temperature flap motor).

 

If it's just air in the matrix, it should sort itself out over the next few drives.

 

 

 

Edited 26 June, 20197 yr by Wino

Get the vehicle up to operating temperature and feel the heater matrix pipes. If the inlet and outlet are hot there are two possible reasons I can think of.

 

1. The heater flap motor is not working or stuck (easily verified with VCDS)

2. The coolant flush has loosened the oil/sludge which is now stuck in your heater matrix

Edited 26 June, 20197 yr by Tech1e