# Jetta MK3 no heat - how to heater core backflush



## rweavere (Sep 4, 2007)

97 Jetta GL MK3 2.0L engine
The quick question: How do I backflush the heater core? I was told to take off both hoses at the firewall and stick a garden hose in the 'exit' hose.. which hose is that? Can someone please give me step by step instructions on how to flush it?
The long question:
For a few months now I've had a pretty bad coolant leak around my radiator. For a while I've been just filling the reservoir with water almost daily (avg temp outside was 60 degrees while using water). My engine has also not been heating up all of the way when it is cold out (40-60 degrees) but my vent heat did work. I was going to replace the radiator, but decided to try the 'stop leak' stuff. 
I put that stopleak (i think it was 'liquid copper' or something like that) in my system about 2 days ago. The leak seems to have stopped, but now the engine still does not heat up all the way and there is absolutely no heat coming out of the vents. I went to the parts store to get a thermostat and the guy there told me to try the backflush thing. 
Any other ideas or suggestions?
Thanks!


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## GroveStreet (Apr 23, 2008)

o jesus dude why did you use that stop leak
stuff is terrible. does not work. anything is temporary. and ive seen that stuff clog radiators and heater cores and line engine coolant passages with junk.
no such thing as a fix it in a can. 
and running straight water is bad too. coolant acts as a lubricant to the bearings in your water pump and as an anti- corrosive. and has a higher boiling point.
running straight water will cause rust. and water is a terrible lubricant also. your damaging your water pump, and your motor as well as the rest of your cooling system

my suggestion is to do things right. replace that leaking radiator and at this point propably your heater core. and flush the system multiple times with a good coolant flush.
plus after a good flush you can run different coolant if you wish. to avoid expensive g12. just make sure its a long life coolant. ive been running dex-cool for 2 years now which is pretty chemically similar to g12


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## rweavere (Sep 4, 2007)

*Re: Jetta MK3 no heat - how to heater core backflush (rweavere)*

Can someone tell me how to backflush the heater core? I guess I will just pull the hoses out and stick a water hose into the left side. Will someone at least tell me if i can break something by flushing water through the wrong side?
Thanks.


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## GroveStreet (Apr 23, 2008)

no your not gonna break anything.. thats how a backflush is done.
im just giving you the real news. that stop leak is just gonna clog up your heater core if it isnt clogged already.
atleast flush the WHOLE cooling system to get that junk out of there.


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## rweavere (Sep 4, 2007)

UPDATE:
Replaced the thermostat, the engine runs at the proper temp now!
Flushed out the heater core, several clots from that stop leak came out, but still doesn't work, I'm going to flush it out again tonight to see if more built up.
Thanks for the advice GroveStreet.


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## roxshot (Nov 23, 2009)

Good to hear you made progress rweavere. Please continue to update this thread, I'm having a similar problem with no heat after replacing the coolant flange.


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## rweavere (Sep 4, 2007)

*Re: (roxshot)*

My update isn't good. Flushed out the heater core again... it was clear(should be coolant). I pulled out the supply line, but it seemed clear so I don't know what to do now. I will drive it tomorrow and see if I have heat, but it's not looking hopeful.


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## rweavere (Sep 4, 2007)

I HAVE HEAT! and then I looked down at the temp gauge and it was almost pegged out








But I do have coolant flowing through the heater core because both supply and return hoses were hot.
I think the leak stop that had stopped the leak in my radiator must have gotten pushed out. 
Looks like I'll be replacing my radiator.


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