Sillyhead

2000 S4 B5 quattro manual. Has anyone ever tried to replace heater core by cutting through the firewall? Then welding it back in place when finished?

HL-240

I helped my friend replace the heater core in his S4, it's really not that bad a job. If we did it again working solidly without getting distracted it would probably be doable as a 3 hour job, maybe a bit more once you budget for flushing the coolant etc.
This video was very useful.

Also, the heater core has to come out the top of the housing that it sits in, so the dash has to be out of the way - i.e. cutting a hole in the firewall probably wouldn't help that much.

AudiAllTheWay

Is the heater core plugged / not producing cabin heat? Or is the heater core leaking coolant?

I have flushed several plugged heater cores with 100% success and without having to replace the heater core.

A leaking heater core is an automatic replace via a dash pull.

SCarGuy

This is beyond hackey, I don’t even know where to begin. Why ruin a firewall? The amount of things you would have to move just to be able to safely cut and weld would be far better spent doing the job the right way, if it needs to be done at all. Most times, a
proper flush with CLR will solve a truly clogged unit

Sillyhead

Thanks for the responses and sorry for not responding earlier. I ended up doing it the correct way,. Obviously I was thinking lazy and simply off kilter. The car sat for two weeks because it wouldn't start after putting dash back. Finally found out a (secondary? Not the main one) sensor for the clutch (one I hadn't unclipped, I unclipped the main one ) needed to be plugged back in. Now all is well. Two weeks later I hit something on highway and needed all four wheels straightened !