sullyj

I meant to respond to you earlier on the resolution. The heater core was clogged and once cleared I have enough heat to warm an igloo. Unfortunately, the first indy shop I took car too failed to properly diagnose and the cost of that heater control valve and labor wasn't cheap. Needless to say they'll never see my business again.

volvopentaman

Seems to be same problem as I have.

I have traced it down to both heater cores internally falling apart. Have swapped both thermostats (main and inline tranny), have pulled the heater valve block apart and swapped coolant several times without any results

Problem is always temporarly fixed by blasting the heater cores through with pressurized air every 2-4weeks.

Will probably replace heater cores with brass ones aftermarket for like 125€/pc instead of 3-4x the price for OEM aluminium ****.

djharm

I think I also have that same problem. After flushing the heater cores the car gets really hot but slowly it gets less and less hot.
They told me to replace the cores but I am just wondering why they clogg up. The stuff comming out looks like white sandy crystals.
Which are now to be found throughout the whole coolant systhem (I did a radiator flush to check). Doesn't look like a heater core breaking down.
So I want to flush the whole systhem first, maybe someone ones put some sort of stop-leak stuff in it.
What kind of stuff are you getiing out after a flush?

Mister Bally

The aluminum reacts badly to improper coolant and water with minerals. Best to mix the proper coolant with distilled water. If you put green Prestone in, the eventual damage is irreversible.

djharm

audirb

Interestingly I have had similar, although not identical, symptoms on my 2017 S8+. For the second time I took my car to the dealer today. Not sure if this will fix it, but there was a TSB issued on Nov 30, 2018 (64F3) that was performed on my car regarding the "Coolant Breather Line" which is replaced under this campaign. This TSB was issued to address "Insufficient heating output". The models listed are MY 2016-17 S8+, so a rather limited set of cars, unless there are other TSB's to address other models.