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Heater Core Flush: An exercise in overthinking

3K views 4 replies 4 participants last post by  jjpark 
#1 · (Edited)
First post. My parents gave my son their old 2000 Passat for his get around car. 110K miles. Absolutely no heat at all. I mean ice cold air.

So of course we dug around the forum and on youtube and saw all sorts of solutions using CLR, air compressors, jet washers etc... We finally got around to do it and were going to connect a pump up with hoses to recirculate hot water and CLR through the core for an hour or two. I had some extra hose in my workroom and we were ready.

So on the last warm day of the year this week we disconnected the heater core hoses and found out that my extra hose was old and inflexible. It would not get around the heater core connections. I only had one other piece of hose that did work but that only covered one side. Seeing that we only had a couple of hours of daylight and thinking of all the warnings about the plastic connectors and the potential for damage we were going to shut it down and try again another day. We just didn't have time to drive around for more hose.

BUT, I did happen to have this in my workroom.

Wood Wood stain Table Plywood Hardwood


It just attaches to the water hose and concentrates the water into a thin jet. So just for kicks we hooked it up to the hose, stuck it in the open heater core and started back flushing the heater core switching sides every minute or so. The amount of dirty crud that came out was amazing. My son started taking a small clear water glass to catch it coming out of the one hose we connected and we kept switching sides until the water was clear and running a lot faster through the core. It took about 10 minutes.

Hooked it all back up, bled the system and now he has plenty of heat. Will it last? Who knows, but it certainly helped.

I know this is not the most thorough way to do the flush, but if you ever get in a pinch and just want to try something simple this worked on our Passat. When it stops delivering heat next time we will likely do something more thorough with CLR and stuff, but for now it works.
 
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#4 ·
I had to run hose from behind my house to the tune of about 75-100 feet of hose. That fact alone lowered the nozzle pressure. So it shot out pretty well, but it wasn't like a pressure washer. You do raise a good point though. If you are running a short hose from a nearby faucet with good water pressure you might want to start out slow and work up a bit.

It seems to me that a nice way to test it would be to start low and see if you get any water output at all. If you do give it a chance to start clearing it. On mine the water initially came out the output side in what I can best describe as half flow. The flow from the output did not fill up the output tube. At least at first. With each successive step back and forth the flow increased and by the end the output hose was putting out a full inner diameter of flow all of which was crystal clear. I hope this makes sense.

If nothing changes then slowly step up the pressure. Not sure how you can guard against blowing an old fragile heater core out, but who can in these scenarios? It is certainly a risk.
 
#5 ·
I just used the open end of the hose and held it up to the plastic pipes. Seemed to work.

I was really worried about breaking the plastic pipes more than anything else. Just about anyone and everyone I talked to warned that if you break them you are looking at dash removal to replace the core but running the car and warming the coolant a bit to warm the hoses made removing the hoses much easier with much less force needed.
 
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