What might cuause a heater core to clog?

BESTBOB

MEMBER
1997 AUDI A6
15,000 MILES

Seven days ago at just over 150K I had a leaking radiator replaced. When driving home that day the heater was working fine. Next day I drove about 110 miles without noticing anything wrong with the heater although the outisde temperature was in the 40s and I might not have noticed if the heat was not working. Car then sat for 2 days. Drove a return 110 miles on the fourth day. No heat (temperature guage at normal level). Returned to repair place. Thermostat in open position. Replaced thermostat. Then was told that heater core was clogged and needed replacing.

The discussion was then about whether or not the wrong color coolant had been added as this could cause the coolant to congeal and clog the heater core. (The cooland was changes about 13 months ago when the timing belt was changed. No coolant added since then.)

And thus this question. What besided adding the wrong coolant (the only time that might have happened was when the coolant was topped off after replacing the radiator) might have caused the heater core to clog?

You can see why I'm wondering re the adding of the wrong coolant. Nothing seems wrong this fall with the heater. The problem arrived soon after that new radiator was installed. So I'm in search of a third party opinion.

2 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Possible the wrong type coolant is used or its not dilluted properly

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Tuesday, December 20th, 2011 AT 4:36 AM

JACOBANDNICKOLAS

MECHANIC
109,709 POSTS

Before replacing the core, we need to check a couple things. The core shouldn't clog the way you described unless, the wrong coolant was used (but you said there was no overheating) or if a product such as Stop Leak was used.

Before we jump to any conclusions, start the car, turn the heater on, warm the engine to operating temp, and fell both heater core hoses. Both should be hot. If they are, then check the blend air door operation. If only one gets hot, then allow the engine to cool and remove both heater core hoses. Using a garden hose, spray water into the core to flush it. Do it in both directions.

Next, replace the hoses, make sure the coolant is full, and allow the return hose from the heater core to remain loose to evacuate any air pockets. Once air is out and coolant is leaking from the hose, tighten the hose, recheck coolant level, and see if the heater works better.

Let me know if you have questions or how things work out for you.

Merry Christmas,

Joe