A4 Heater blows cold unless the car is driven or revved

[maersk]

Partially blocked heater matrix. Remove both hoses from the matrix and back flush using a garden hose - the pressure should be high enough - make sure you identify which way the coolant is circulated normally and make sure you do it the other way round.

You will of course lose your new coolant inhibitor!!!

Probably the reason for the blockage is a lack of inhibitor from your (not you personally) first head gasket change. Ally heads are very fussy about their coolant additives.

[stuartxrv]

Once again, thanks.
My only arguement against that theory though is that the flow rate alters with engine speed. If there was a blockage then i'd pressume the flow of coolant woud be constantly poor? With the engine at 2000rpm, after a minute the coolant comes squirting from the matrix hose and maintains it once i've dropped the revs to idle. Only after 5 mins of replacing the hose and clip does it seem to drop again!
I've also noticed that my engine temp doesn't get higher than 90 and my fan never kicks in. Got back from a run today with engine temp at 90 and opened the bonnet, left the engine running for another 20 mins but the temp didn't raise nor did the fan kick in. Maybe it's just the ambient temperature thats helping to keep the engine cool!?

[maersk]

Still sounds like above - partial blockage.......................

[stuartxrv]

Cheers,
I'll give the hose pipe a go next week. Let you know how it goes!

Regards
Stuart

[stuartxrv]

My appologies,
back flushed the matrix this morning and was amazed at the crap that came out. Heaters now working at 70%. Going to try filling the matrix up with coolant flush/hot water and see if it removes any more.
Feel like i'm about to close this chapter.
Thanks for all your help.

Stuart.

[maersk]

Go for it get a flusher in there and do it again next week!


Always had success with this..................

Started with Imps in 19**...................... don't say it