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The cooling system should be bled any time the water in the reservoir has been very low, or the system
has been opened (other than the filler cap).
NOTE: The V6 has 2 extra bleeders, one is on the hard pipe about 6" below the coil pack connector,
the other is on the hard pipe about 4" below the CPS on the back of bank 2, these should be bled first,
then finish with the heater hose bleeder.

Bleed the cooling system with the engine NOT running. Disconnect the plug to the level sensor on bottom of the reservoir and raise reservoir as far as you can (cap end about 4") and prop up while bleeding.
The bleeder is where the RHS (US Passenger) outlet heater hose (with white marking) connects to the heater core, undo the clamp and move the hose until the bleeder hole is open, use a small screwdriver or wire to check that the hole is fully open.
With the Reservoir raised and the bleed hole open, pour coolant into the reservoir slowly until it runs freely out the heater bleed hole without bubbles, push hose back to original position and tighten. Reattach sensor plug, mount reservoir and top up.

Drive a few miles and recheck level.
To be totally sure, you could repeat the above procedure after driving several drive cycles.

Bleeding Notes
When bleeding; the car must not be on a steep slope.
The coolant level in the reservoir must be kept higher than the bleeder and the cap must be left off until
after the bleeder hose has been clamped.
Coolant must be flowing freely and smoothly through the bleeder when refitting the hose.
The engine MUST NOT be cranked or started while the bleeder is open. (Air would be sucked into the system)
The position of the heater controls has no effect on flushing or bleeding.
If the bleeding process is carried out correctly, there will be no air left in the system.

Always reverse flush, connect the feed hose to the outlet (the one with the bleeder), and the drain hose to the inlet.
You will need to obtain a high flow, without reaching high pressure in the core. The valve in the cap is designed to prevent the system pressure from exceeding 15psi, I suggest you don't allow the pressure in the core to go much over that.
NOTE: A CLEAR CORE will easily take all the flow you can get from a 1/2" garden hose, without building up pressure in the core.

You should NEVER FORWARD FLUSH a core with any blockage, this would be unlikely to help much, and is likely to pack the core so tight that you may never remove the blockage with any method.

I suggest you try this method. (see the homemade tool.)

OTC 6043 Blast-Vac Multipurpose Cleaning Gun : : Automotive

Your options are:
1: Do nothing. (Shiver)
2: Replace the core. (Big job)
3: Flush the core clean. (Small risk of damage to core if careful) Worst case you still have options 1 & 2.

If you want to use a chemical solvent (such as CLR or Citric Acid), first reverse flush with water or water and air, then blow the water out of the core with air, then fill the core with chosen chemical and allow to soak. Repeat reverse flushing. Finish with a forward flush.

Heater Core Swap - PassatB5


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