Very sage, approach, DD. One thing I wondered about when back-flushing a heater core was for the bad stuff, if any is in the core, to end up loose in the cooling system and possibly clog up the radiator core and/or a radiator hose, with even more disastrous results. Your method seems to eliminate that risk as much as possible.
Since I don’t have access to a garden hose set up, being an apt. dweller, I guess I could attach clamps to the ends of both the added hoses and drive Superblue to the car wash and use a pressure wand to do the same thing, right?
I think a pressure wash would be way too harsh, better to just use a hose attached to a normal water tap if you can rig something like that up at the car wash, or talk to a friendly service garage?
Was talking to a tech bud of mine about that and he agreed with you. However, I mentioned the “spot-free rinse” operation, which puts out even less pressure than a garden hose, IMHO, similar to a rain shower, and he said he thinks that would be safe to go with.
My smart-@$$ question is how are you going to drive it to the car wash after the hoses are disconnected and sitting with heater core cleaner for 12 hours?
As long as you are doing this I suppose you should buy the extra length of hose and connect the block flow, bypassing the heater valve and heater core until after your flushing activities are completed
Oops - didn’t think about that - at least other than also clamping off the heater hose ports somehow at the other ends (i.e. on the engine block)! I guess I was assuming the “loop” in the system that goes to/from the heater core doesn’t hold enough coolant to undermine the engine cooling function in general. If so, then I could run a temporary bypass hose connecting up the heater hose ports.
So I disconnected heater hoses to core, I was easily able to blow out core water with my lungs. Input some CLR in there for 5 minutes, flushed with garden hose. Nice and clean came out.
I’m currently soaking the core with vinegar now, will flush again later.
But I’m thinking my core is not clogged…I will probably investigate if the vacuum is being applied to the new heater valve I installed when it shouldn’t. I know my upper vents sometimes come on during heat when they shouldn’t. I could have some malfunction or vacuum issues with MK3 system…
Georg, I think I have the same problem as you. Because the engine heats up quickly, and when I turn on the air in the cabin, nothing flies. I’m trying to get to this heater / device over the passenger’s legs and check. Does he work well with you?
CLR, eh? I have still have an old jug of that stuff and can’t even remember why I originally bought it. Sounds like it’s worth a shot using on Superblue …
Can you just place a finger over the vacuum hose when the switch is on to see if you feel a vacuum being applied (can you guess - I don’t have a vacuum gauge ) ?
Your method seems to eliminate that risk as much as possible. 
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