schranzkt

Drained coolant for service on the car

At idle the car ran at operating temp no issues.

I attempted to bleed the coolant system at the bleed screw behind the plenum on the firewall and it flowed out very consistently. Still no heat

However when I took it for a drive it blew out the overflow on the coolant reservoir and the heat isn't working. I have the red coolant warning symbol on the dash.

How do I bleed this off? I am used to just pulling the heater core hose off on my B5.5 passat

2004 A8L 4.2

MP4.2+6.0

1. Two bleed screws, not just one, so be sure you have found both. Can be on either side of firewall.

2. 2004's are more notorious, apparently due to (lack of) a helper hose in radiator area. If yours is original, may be in that problematic group. Folks who have replaced radiators over years find the replacment has another hose outlet you then retrofit in to system. I think that was revised by like early or mid 2005, so it goes back to the "2004" teething stuff. Meantime, Bentley, TSB's, etc. call for a pressure type bleeder set up to overcome this. I had no issues with 2000 4.2 A6, but then probably different specific hose set up.

First be sure you are working both hoses for bleed screws. Then you may need to resort to pressure bleeder. Sometimes doing bleed screws and just heating up idling at home with near full reservoir and then letting it cold cycle can pull the coolant back in when it cools. Refill after cold again and no pressure. If it "burps" the big air blockage one way or another with approaches like these short of a pressure assist set up, then the small bubble stuff can often just work way through in a few days. Forcing AC to run by pushing interior temp settings down to minimum can also help get radiator to heat more evenly with the fan running full time to avoid hot spots if coolant fill erratic. But let it get somewhat warm first to avoid a lot of extra overall run time to get up to operating temp. Cycling back to full hot interior settings periodically of course too to try to get water though heat exchanger panels and air to bleed screws area.

schranzkt

so you were right! There are 2; side by side. The inner most one was bone dry. The outter one was steadily flowing. I finally got fluid to both but still my heat wasnt getting better. When I drove i felt it maybe getting slightly warmer but nowhere close to where it needed to be. At least this time the car didnt overheat and spill out the relief

Should I keep driving it and hope it works itself out? Maybe Drive a little, come back and bleed? Should I bleed both open or one at a time? How open should these screws be?

MP4.2+6.0

Yes, two. Open until they pee out consistently, not just spurts. Do one at a time. If you have helper, you get more flow via water pump if you rev it up to 1500 or 2000 rpm--then both should have some pressure as you open them.

Sure, can try to drive as long as it doesn't boil over. Only open cap to add more when motor cold--not just so it doesn't spill all over but because you want the advantage of the fluid contraction as it cools along side the pressure to get coolant into harder areas. Also if you can reach upper hose, try squeezing it when cold to force coolant to move around. Both with fill cap on and tight, and then also off. On a lot of cars, massaging it like that when you first fill it can get in another quart or so.