Best Way To Flush The Rear Heater Core?

Best Way To Flush The Rear Heater Core?

Postby ri$e*above [OP] » August 6th 2020, 2:34am

I'm not getting rear heat on my 2002 Safari AWD. The front heat is good, but the rear is just blowing regular air. I'm going to flush my coolant system, and was wondering what's the best way to flush the rear heater core? I don't have rear AC if that has anything to do with it.

Cheers
CURRENT: 2002 GMC SAFARI AWD SLE 'GOLD DIGGER'. 5 INCH LIFT. G80. GT4.
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Re: Best Way To Flush The Rear Heater Core?

Postby MechBob » August 6th 2020, 2:43am

Before you get carried away,there is a separate vacuum and electrical controlled valve that controls coolant flow to the rear heater
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Re: Best Way To Flush The Rear Heater Core?

Postby ri$e*above [OP] » August 6th 2020, 2:45am

MechBob wrote:Before you get carried away,there is a separate vacuum and electrical controlled valve that controls coolant flow to the rear heater

I was reading something about that. Is the vacuum and/or electrical control valve known to fail? What's the best way to check if it's broken?
CURRENT: 2002 GMC SAFARI AWD SLE 'GOLD DIGGER'. 5 INCH LIFT. G80. GT4.
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Re: Best Way To Flush The Rear Heater Core?

Postby markmitch » August 6th 2020, 2:47am

well first thing I would do would be to disconnect the lines that run to the rear heater system and see if they are clogged. Then to clean out the whole system drain the radiator, stick a garden hose in the filler tube leave the petcock on the radiator open let the hose run on low to barely keep up with the drain start the engine and let it run till the coolant comes out clear. Then remove the hose , close the petcock on the radiator. take one gallon jug add 1 cup cascade dish water powder fill it up with water shake till dissolved then add it to the radiator fill with water. Start it and let it run for 40 or so minutes making sure front and rear heat are on. This should clean it out good. Drain flush again with hose to clean out cascade remnants then refill with distilled water and anti freeze. Do not mix green and orange antifreeze.
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Re: Best Way To Flush The Rear Heater Core?

Postby MechBob » August 6th 2020, 2:58am

When the rear heater switch is turned on,it activates the solenoid, which allows vacuum to flow, which opens the heater valve.
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Re: Best Way To Flush The Rear Heater Core?

Postby ri$e*above [OP] » August 6th 2020, 3:05am

markmitch wrote:well first thing I would do would be to disconnect the lines that run to the rear heater system and see if they are clogged. Then to clean out the whole system drain the radiator, stick a garden hose in the filler tube leave the petcock on the radiator open let the hose run on low to barely keep up with the drain start the engine and let it run till the coolant comes out clear. Then remove the hose , close the petcock on the radiator. take one gallon jug add 1 cup cascade dish water powder fill it up with water shake till dissolved then add it to the radiator fill with water. Start it and let it run for 40 or so minutes making sure front and rear heat are on. This should clean it out good. Drain flush again with hose to clean out cascade remnants then refill with distilled water and anti freeze. Do not mix green and orange antifreeze.

Thanks.

Do you think it's worth doing a flush/back flush on the heatercore/s separately before doing a whole system flush? Have you tried a chemical cleaner like the Prestone stuff, or did you find the Cascade powder works real good?
CURRENT: 2002 GMC SAFARI AWD SLE 'GOLD DIGGER'. 5 INCH LIFT. G80. GT4.
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Re: Best Way To Flush The Rear Heater Core?

Postby ri$e*above [OP] » August 6th 2020, 3:07am

MechBob wrote:When the rear heater switch is turned on,it activates the solenoid, which allows vacuum to flow, which opens the heater valve.

Thanks.

If I have a faulty solenoid, would the dash switch/fan still work?
CURRENT: 2002 GMC SAFARI AWD SLE 'GOLD DIGGER'. 5 INCH LIFT. G80. GT4.
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Re: Best Way To Flush The Rear Heater Core?

Postby MechBob » August 6th 2020, 3:11am

If you just want to see if it is plugged, pull off the hoses,you can do this up front,and run water from a garden hose into them, see what comes out.Do not use full pressure or volume, use a valve on end of hose.
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Re: Best Way To Flush The Rear Heater Core?

Postby MechBob » August 6th 2020, 3:13am

A bad solenoid has nothing to do with the blower
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Re: Best Way To Flush The Rear Heater Core?

Postby ri$e*above [OP] » August 6th 2020, 3:18am

MechBob wrote:If you just want to see if it is plugged, pull off the hoses,you can do this up front,and run water from a garden hose into them, see what comes out.Do not use full pressure or volume, use a valve on end of hose.

Should I flush the main hoses for the front heater core and that will also flush the rear heater core? Or does the rear heater core have specific hoses on the heater control valve that I should flush? I'm guessing it's all looped into the main system?
CURRENT: 2002 GMC SAFARI AWD SLE 'GOLD DIGGER'. 5 INCH LIFT. G80. GT4.
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Re: Best Way To Flush The Rear Heater Core?

Postby MechBob » August 6th 2020, 3:25am

There are separate hoses going to the rear.Passenger side of engine compartment,you will see the 2 valves and all the hoses.
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Re: Best Way To Flush The Rear Heater Core?

Postby maximus7001 » September 7th 2020, 8:59am

Did you ever figure this one out?
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Re: Best Way To Flush The Rear Heater Core?

Postby Leeann_93 » September 7th 2020, 3:38pm

Slide underneath behind the driver’s seat. Near the fuel fill, you will see this:
Image

Pull the hoses to see this:
Image

Stick a hose in, flush till clear, reverse sides. Reclamp hoses. Done.
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