2012 Q7 3.0TDI no heat whatsoever

[siral3x]

Friends Q7 TDI. Cooling fan died and it overheat. He got it to me in limp mode from being overheated, and figured out upper hose cold and no coolant flow. Replaced thermostat and water pump and cooling fan. (Found stuck melted tstat)

All seems well and got coolant to flow again in expansion tank(stone cold before), but there's no heat in front or rear unit and still overheats.

Stopped up heater core? This thing has 2 one in front, one in back. So both heater cires stopped up??? Seems odd also can't seem to find heater hoses in engine bay on this TDI?

Blows ice cold AC, no heat whatsoever.
Note: lots of corrosion in old coolant and wrong coolant was used. The rad hoses were "crunchy" feeling when squeezed when I first got it before draining old coolant etc.

[jbain2]

There still may be air in the lines. I know in most circumstances the heater core hoses can be the highest point to bleed from. Is that the case with you?


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[siral3x]

Update: got her on jackstands and let her idle today for 30min till she got to 200F.
The rad hoses in engine bay are HOT and the overflow tank is hot and flowing.

I figured out that on the driver side frame rail the heater hoses for the back heater core unit are STONE COLD/no flow. Reached from under the car and the rubber heater hoses were hot, but as they go into the aluminum pipes on the frame rail they are cold so no flow and of course no heat in back.


Not so lucky with the front heater core/hoses. It looks like they are buried under the windshield wiper linkage/motor assembly and can't even touch them is so tight in there, without removing the whole wiper/motor assembly 1st.
Anyways still no heat in front or back and I have no flow confirmed to back heater core.

Does anyone know if the EGR cooler or the OIL cooler between the cylinders are connected in any way shape or form to ANY of the 4 heater hoses that go to front and rear heater cores?

I am trying to eliminate the egr cooler or oil cooler being stopped up. Alternatively I am thinking of working backwards from the rear heater core to front of engine? Gonna try to reverse flush the rear heater core and pipes out...then remove the wiper assembly and bypass the front heater core? (Flush it also).
At that point it will be either egr cooler or oil cooler left on the engine side?


This is a side note, but this is probably the WORST engineering nightmare of a TDI I have ever seen, and I have owned a few...but never a Q7/Touareg 😳 This is a friend's car, I am trying to help them out.

[VinnysS4]

I know it's a long shot but have you tried an Airlift to bleed the system?

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[siral3x]

Update:
The heater hoses get routed in the driver side wheel well, so I took the tire off and the splash shield/fender shield and found them to be stone cold.
Found a coolant bleeder port on top of a metal line... 10mm screw comes off the oil cooler i think and burped the system.

A lot of air/steam came out that port and the heat came back ON and the aluminum heater pipes in fender well are HOT now so I know there coolant flow.

The front vents blow sorta hot/Luke warm not super hot.
The rear unit BLOWS COLD air despite the fact that the aluminum heater pipes that run all the wait back to the rear heater core are HOT now.
I suspect a clogged rear heater core, and partially clogged front one as the air is luke warm coming out of the front vents.

Anyway I am making progress BUT this thing is a clusterfuck. Still overheats but takes longer and can be driven short distance STILL have work to do but progress is made.

I am thinking of bypassing temporary both heater cores as they all join/togheter in the driver fender well 2 pipes from motor come down by axle and then split into 4 aliminum pipes(2 for front heater core unit) 2 for rear unit and a 2nd electric aux coolent pump hidden in fender well for back heater core?WTF AUDI. Can be bypassed by doing a loop on the 2 pipe that come from the motor.... and both heater cores bypassed to test?

[VinnysS4]

I'd fix the overheating issue first. Either there is a lot of air in the system, or there is something wrong like a leak causing the coolant to depressurize, or something like a stuck closed thermostat or faulty water pump.
Personally, I'd drain the coolant, pull a vacuum with my airlift and see if there are any pinhole leaks. If it passes a leak test, I would use the airlift to fill the system. That would ensure 100% that all the places that hold air would be filled with coolant. In complex vehicles with rear zone climate setups, its almost mandatory.

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[siral3x]

I will drain coolant and do a vaccum test soon.
The thermostat and water pump was just replaced. The old Tstat melted and stuck closed...