Replace coolant after replacing a heater core?

"Mark" wrote

That can be taken two ways. "Replace" *lost* coolant from the loss of coolant that was in the core and what little may have spilled out.

If it said, "completely replace coolant" it would be different. Obviously, any coolant lost HAS to be replaced and it is impossible to do the job without having to replace some coolant even if it is pouring (figure of speech) coolant from the old core into the tank (not saying to do this).

It IS an opportunity though for old (not yours) coolant to be completely replaced while a person is working on it. If I did this I would backflush the whole system. You can buy a self back flush kit (not as good as the commercial stations) that works very well for 5 or 6 dollars at discount parts stores.

You do not need to completely change the coolant if clean. Just replace coolant lost obviously. That is what they meant, imo.

Harry

In addition I might suspect that if the core went, who knows what might have gotten into the coolant and now resting in the radiator. A flush and refill with fresh, is what I would do.

I think I have read somewhere in the VW documentation, that the coolant has additives which form some sort of protective layer in order to inhibit the corrosion. Apparently, the fresh coolant does it much better as the old "used" coolant.

On the other hand, if you changed the heater core, you probably flushed some significant amount of coolant anyway, and then topped it up (hopefully you didn't filled the old one + some water).

In general, if I was you, I wouldn't do anything. Or just buy one bottle of G12+ concentrate (its 1.5 liters and maybe some $10 (or you are being ripped)), suck some of the coolant out and the top it up just with that concentrate. It will not significantly impact the freezing resistance of the mix and will get you some fresh additives floating around :)

That's an interesting thought... that only new G12 coolant has the ability to 'treat' a fresh heater core. Can anyone verify this theory?

I mixed G12 coolant 50/50 with distilled water and added that to the cooling system after the restart. No, I did not pay more than $10, I paid a little more than $8 on germanautoparts.com.

snipped-for-privacy@>

"only new G12 coolant has the ability to 'treat' a fresh heater core"

I wouldn't go that far. But, chemically speaking, old coolant has lost (chemically converted) a lot of its corrosion-protecting components over time. So new coolant will protect better than old.

I have to top post this. Good post. Its ironic how some people do half-assed jobs and then congratulate themselves on the net. My hat off to you for trying to make a difference...

[snip]

You don't have to top-post. Ever.

The assumption is that the heater core failed due to corrosion. That is of course *seldom* the case in the 10+ million VW that need the core change. In those, it's because the seal of the ends of the core has failed or is likely to fail due to a design flaw.

"Bernd Felsche" wrote

That is exactly, absolutely, 100 per cent correct. I am glad someone posted that. The core I recently replaced looked fine except the "seal at the ends" failed. Every core I have ever done had a clean liquid path and mostl/if not all all, leaked on the end where it is affixed to the sidemembers,

In fact, most cores are aluminum or copper and just about never fail to corrosion plus the coolant path should never have been corrupted because the coolant leak flows *out*, obviously, not in.

For someone who has *recently* changed their coolant there is **absolutely no reason** to completely replace the coolant, which, by the way, is obviously not like lubricants and has a much wider margin of acceptability than lubricants for contamination, just a heat transfer medium, however, a recent coolant change before the work should have little or no contamination or degradation.

Harry

Thanks Harry,

Your opinion is the one that rings true to me. I am not into doing any job halfway, but I have _completely _ replaced the coolant completely several times over the years on this car including once just a few months back. This heater core did not rot out, it popped open. My coolant is still clear pink in color so I think I will leave it at that.

Thanks to all.

Mark

Harry wrote:

I did replace one which failed. It was an aluminium core in my Audi

100, and started to leak directly in the middle. I am fairly sure it was due to the Prestone coolant I used at that time. So, the aluminium cores fail to corrosion too.