My mom has a 1999 Taurus 3.0 liter v-6, 52000 miles, that had low heater temp output when driving at highway speeds. We have had the heater core back flushed and it works alright at highway speed but now it is cold at idle when stopped at traffic signals. We have had the thermostat replaced with no difference. We then had the water pump replaced with no difference. The only way we can get the temp up is the choke off the bypass hose across the heater core. What is the purpose for the bypass hose and what else can we do besides choking the bypass? Thanks for your information.
The bypass hose is there because the Vulcan motor has a bad habit of clogging up the heater core. If the hose was not there and the core plugs up then the back head gets no coolant.
We ended up having to have the heater core replaced and that solved all of the problems. I assume that the backflush could not get all of the sediment out of the core but just enough to help a little bit. I wonder if there is some kind of an inline filter that could be installed on the inlet side of the heater core to prevent this from happening again, since it was an expensive resolution, in a relatively short period of time?
Years ago I diligently flushed my fiancée's '93 Shadow on several occasions. Due to the hardness of her well water I was inadvertently introducing calcium, lime, etc. into the cooling system. Within a few years I had managed to plug the heater core pretty well.
I tried several chemical flushes of just the heater core, but no dice. I think once those hard minerals build up in those tiny passages, you're done for.
Assuming the input hose to the core is plenty hot, replace the heater core. It's the only thing left at this point.
Don't forget to check the heater controls, blend door, just in case.
For what it's worth, it sounds like a little diagnosis would have save you a water pump replacement.
FWIW a couple of gallons of vinegar or the water treatment Iron Out powder mixed with water make a good flush treatment and will remove the hardness minerals.
But you should always mix your antifreeze with distilled water.
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