[CntrlNJPassatGuy]

I was getting NO HEAT out of my vents...5 or 10 degrees above ambient...Tops. Made the last two weeks here in NJ a real joy. I took advantage of the first above freezing day here to do a backflush. I backflushed my 2000 V6 ATQ today for two hours. 1/2 gallon of CLR and 3.5G of hot (when I started) water using the set up lots of guys on youtube appear to using. A 1/10 HP Drummond pump connected to the outlet (passenger side) of the heater core, and heater core inlet into the bucket of 'cleaner'.

Lots of rust and silt but no big chunks. Temperature now ambient + 50 degrees. Thank god!! Got too dark to do a complete bleed of the core but the OUTFLOW appears to be running very slowly. Will this improve if I flush it again? Will I gain more heat by doing it again for longer? That would have to wait for Spring.

An instant read thermometer shows 128 degrees F. Can I expect it to go much higher?

Thanks for the hand.

 

[VAGguy]

I guess I should measure mine, but my 1.8T has always been uncomfortably hot at full tilt. Think about it though. At temp, the coolant is 190F. Through the heat exchange process and losses due to temperature of the surrounding duct work and metal I would expect 130-150F out of the vents.

 

[AndreasPassat]

I guess I should measure mine, but my 1.8T has always been uncomfortably hot at full tilt. Think about it though. At temp, the coolant is 190F. Through the heat exchange process and losses due to temperature of the surrounding duct work and metal I would expect 130-150F out of the vents.

I'd say that's a fair assessment.

 

[bvariant]

I've actually done the experiment in a little detail recently. I think the answer is probably close to 180F for a new heater core, somewhere in the 150F range for a mostly well functioning one, and 130F for one that is wimpy in usual New England January temperatures, which are about 20F in the morning.

By way of background, I can give you some history that might be helpful. First, my heater core partly silted up years ago after an ill advised "oh, it's really G12 compatible" sale of a flush from my otherwise mostly reputable tire shop. That led a few months later to cloudy coolant, which I replaced after a month or two of noticing.

Before that, the dash vent output was almost painfully hot to touch after about 15 minutes of running the car at an ambient temp of about 20F. Afterwards, despite every 2 year flushes without pressure or CLR, it gradually shrank over a couple of years to wimpy warm with the manual heating system blower on fan setting 2.

At that point, I started measuring with a refrigeration dial thermometer stuck through the vents in the middle of the dash after about 10 minutes of the engine running. That got me at worst about 120F at blower speed 2, which dropped to close to 100F coasting downhill in neutral (800 rpm). It turned out that my thermostat was stuck partially open. This led to a thermostat replacement and a couple of flushes including one with CLR (last one about 18 months ago).

Since then, at an ambient temp of 45F, the vent output has been at about 140F-160F for blower speeds 0-2 at 60 mph (roughly 2800 rpm?) when the car's warmed up for about 10-15 minutes. It's a little less than optimal at 20F outside, when I can't run the blower more than at setting 2 (140-150F) without the vent temperature dropping off to the 120's-130's. It's also warmer at highway speeds, when the water pump runs harder and presumably forces a little more coolant through the heater core.

I have to confess, I'm wimping out and ordered a new (2018) Allroad in part because of this. I absolutely hate lousy heaters. Probably dates from the early 1990s when I ran an Opel 1900 with a leaking heater core far too long during the winter. I hated the hour drive with gloves and hat, wiping the condensed coolant off the windshield...