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2004 B5.5 Variant 1.8T
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Yuck. That is one job I hope to never need to do on mine.


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Discussion Starter #123
97904


Ok added the heater core back into the system. I'm getting 180F at the vents so I must be circulating, but it's sitting at 226F now. Am I in for a new heater core at this point? If it's flowing I can't see why that would cause such a big change.
 

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Discussion Starter #124
So I know everyone swears a clogged heater core can't possibly make a car overheat. But my experience today shows that may not be accurate. With no heater core I was idling for a very long time at 194F. Once I added the core in the temperature jumped back up over 30 degrees. Seems like something to do with the heater core is causing this.

Anyone have an explanation for this? BTW, I did flush the core with CLR multiple times so I won't be doing it again.
 

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For the heater core to restrict flow to the point that it causes overheating, it would have to be really plugged.
Seeing as how the previous owner had mixed G12 with regular antifreeze, I can see that being the case.

These are the fittings I used to blast out my heater core and engine block.
I couldn't find the actual heater core fitting, but you get the idea. The valve is key - open and close it to blast out the sediment/etc.

I connected the 2nd fitting to the heater core hoses and had the lower rad hose off.
97905
97906
 

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Discussion Starter #126
I honestly do not believe I need to flush it again, and I am getting plenty of heat and I already flushed it multiple times. I just can't explain the 30 degree difference when adding the core back into the system.
 

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I just saw you poking around in the DIY heater core swap thread. Posted this for you to give the core a good blasting if you're contemplating that step. If you have heat, problem solved - stop looking and be thankful.
 

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Discussion Starter #128
I just saw you poking around in the DIY heater core swap thread. Posted this for you to give the core a good blasting if you're contemplating that step. If you have heat, problem solved - stop looking and be thankful.
I have heat but when I bypass the heater core I'm fine. When I put it back in the system I overheat so there's something going on...
 

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I have heat but when I bypass the heater core I'm fine. When I put it back in the system I overheat so there's something going on...
I wonder if something in your core (including the bypass) is really really really restricting your flow.
I currently run my heater core backwards, perhaps you could give that a shot for a little while and see if that resolves or moves any gunk out.

just in case it isn't obvious, take the left hose (outlet from core,has the bleeder hole) and put it on the right nipple (inlet to core) on the second firewall, visa versa.
 

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W/O reading back thru 6 ppg, I trust that you have been only reverse- flushing the heater core?
Yes I've only been reverse flushing the core.
I understood it as well that you were reverse flushing the core, however I am saying RUN the core in reverse, not flush.
The last 400 miles or so (The passat is not my daily driver) I have ran the core backwards without any issues from the core.
I do have a leak in the gasket under the intake manifold, but that is another issue.
 

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Discussion Starter #133
I am calling it. It is 100% the heater core. Bypassed it again and the temperature dropped 32F. That's not a coincidence.

Also, I'm a trumpet player so you can trust this next test as accurate haha. I took a hose and blew through The new one I got. It took all the air I could push. I did the same with the old one and it could barely take a quarter of my air...
 

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Discussion Starter #137
25 minutes in with reversed hoses on the heater core.

97909


It's better than the 225F I was getting with the core, but not by much. I'll be willing to drive it a bit and see what happens.
 

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I would suspect that the longer you run with lines reversed, the more " brown sand " you will dislodge from the heater core fins. When you think you've run it long enough to test, crack the radiator drain valve and see if any of that sand comes out.
 

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This is strange, but I guess possible. The lack of coolant return flow would force more coolant through the oil cooler, but once the thermostat opens, there should be plenty of flow as it then could bypass the heater core through the radiator. Perhaps that would require higher rpm to get enough flow.
 

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Discussion Starter #140
This is strange, but I guess possible. The lack of coolant return flow would force more coolant through the oil cooler, but once the thermostat opens, there should be plenty of flow as it then could bypass the heater core through the radiator. Perhaps that would require higher rpm to get enough flow.
I have still not seen the thermostat open definitively except once, this morning with no heater core. At 194F, the lower hose and radiator started getting warm.
 
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