I don't want to beat this issue to death but I haven't really found any solutions to my problems after hours of searching on this site and others. Hopefully someone here can guide me in the right direction.
Started with just luke-warm heat when the weather got cold. Bought 1 gallon of G12 coolant, lower rad (G62) sensor o-ring and clip from Audi dealer as well as 3 gallons of distilled water.
I removed both lines from heater core and flushed both ports of heater core using garden sprayer nozzle. Removed a little gunk and both sides flowed well so it's not restricted. Followed the coolant flush DYI and drained, flushed with distilled water (twice) and re-filled system with approx 50-50 mix. Bled the system well and found no traces of leaking and my gauge is right where it should be at 90 (12 0'clock).
It was during this process, I noticed that my lower rad hose never gets warm even after running it at 2000RPM for 3 min (according to Shop-Key procedure) AND idling it for over 1/2 hour AND taking it out for spin on the highway and back. The heat seems warmer in the cabin but not much different from before so I decided it was the thermostat.
Bought an OEM stat (Behr) from Audi dealer and replaced it last weekend, bled the system once again but no change (warm heat and lower hose still cold), temp gauge at 90 and no fluctuations. I pulled no codes from VAGCOM pertaining to the cooling system and I also reset the climate control (HVAC, Basic Settings, Group 001, etc) thinking it may be the flaps not positioned properly.
I tested the old stat with boiling water (it didn't open) but I didn't test the new one to see if it was working properly before installation trusting it must be good because it's brand new from Audi. Also, I didn't know the J plug even existed when I bought the stat so I didn't replace it. I assume that if the J Plug failed, I would have a leak but I don't. So should I be worried that it is contributing to my issues? I also didn't know that I can check the water pump impellers when I had the stat out.
The records (receipt) that came with the car when I bought it says that the T-Belt and water pump were changed at 125,000KM (78,000 Miles) in 2008 and it now has 190,000KM (118,000 Miles). The shop specializes in European cars; BMW, Audi, VW, etc. so I would assume it to have the improved version of the WP.
THE GOOD STUFF:
- No leaks
- No codes, MIL, CEL, nor abnormalities with gauges.
- New OEM stat and proper G12 coolant. Used pressure tester to force coolant into system in addition to proper bleeding of system.
- Expansion tank is pressurizing, gets hot and at correct coolant level.
- Hydrometer (coolant tester) tested for - 30C so it's a good mix.
- Top rad hoses, expansion tank small hose, top hard pipe, heater core inlet hose, lower hard pipe all hot.
- Only warm cabin heat from vents (livable).
- Heater core return hose warm only.
- Lower rad hose stone cold and and stat housing cold.
- Didn't check the J Plug (didn't know it existed at time of stat replacement).
- Didn't check WP impeller (didn't know I could've at time of WP replacement).
The heat I can live with but I'm afraid coolant isn't flowing properly because of the lower hose issue. Am I being paranoid about this because I never noticed a thing last summer (before I did all this) when it was hot (32C / 90F) and I was driving pretty hard some days. There were no indications of overheating, leaks - nothing.
What am I missing?
- Is the lower hose suppose to be cold because it's cold out? It's about -10C/14F now.
- The only thing I can think of is to check the measuring blocks of the two coolant temp sensors but I don't know the procedures. Maybe that will give me a clue.
Sorry for the long write-up.