radiator flush procedure

Sierra54 · July 22, 2005

After replacing the upper and lower radiator hoses and thermostat I am ready to flush the remainder of the old coolant. However, I am unable to follow the instructions in my Chilton's manual as I cannot install the thermostat housing assembly without the thermostat. Both are one piece. Could someone please describe the procedure as to how I can flush the heater core, block and radiator. I have the prestone backflush kit however I am hesitant to cut hoses to install this. Additionally, I could not find the block drain plugs. Is it a large torx or allen type bolt? Any advise on what to look for would be greatly appreciated.

Bish · July 23, 2005

After replacing the upper and lower radiator hoses and thermostat I am ready to flush the remainder of the old coolant. However, I am unable to follow the instructions in my Chilton's manual as I cannot install the thermostat housing assembly without the thermostat. Both are one piece. Could someone please describe the procedure as to how I can flush the heater core, block and radiator. I have the prestone backflush kit however I am hesitant to cut hoses to install this. Additionally, I could not find the block drain plugs. Is it a large torx or allen type bolt? Any advise on what to look for would be greatly appreciated.

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I use a garden hose sprayer and some PVC fittings. I don't remember the dimensions but I screwed a garden hose female into the pvc endcap. I pop the upper radiator hose, connect the garden hose sprayer/pvc thing to the upper hose. I connect another radiator hose to the open radiator inlet for a drain. THe thermostat is reverse poppet so it will open under backwards pressure. You have to be carefull not to use too much pressure as 60psi from a garden hose can do damage. I flush so there is a constant stream but not too fast. After it runs clear for a whiile I reconnect everything anr run the engine up to temp with front and rear heat on hi to flush the lines. Another round with the garden hose and don't forget to flush out the overflow container.. Once everything runs clean, I open the radiator drain and drain the overflow. Add 1/2 capacity of cooling system Dexcool and top off if necessary with water. Bring it up to temp with heat on and then recheck level after cooldown.

I do it every 2 years on my Tahoe. I just can't imagine leaving it in there for 100K like they say. Some people suggest demineralized water (deionized) for the coolng system. The manual says potable water (drinking water). I've been using tap water for 148K and I'm still on my original water pump and radiator so I don't think it's hurting anything.

az'03Silverado · July 23, 2005

Just like Bish said. Back-flush it through the upper radiator hose. You can do it with the thermostat housing off and just go till it runs clear. Be sure to open the heater to full/hot to clean out the heater. Then just flush the radiator and overflow separately. I always do what Bish does, too. Add half the cooling system capacity with Dex and then top off with water after flushing. Oh, the block drains are those big brass hex plugs on the bottom of the block back by the transmission. I'm not sure how hard it is to get those off of there. Anybody know?

One more thing. I'll second, also, that this stuff shouldn't be left in 100K miles. Down here in AZ, the heat kills the hoses anyway so they need to be changed sooner than that.

Valsport · October 26, 2005

When you say to be sure to open the heater by blowing it on hot, does that mean you're flushing while the motor is running?

Bish · October 27, 2005

When you say to be sure to open the heater by blowing it on hot, does that mean you're flushing while the motor is running?

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Nope. Run it until blowing hot while getting it up to temp. Then shut it down while flushing.

brainpause · June 24, 2011

Just like Bish said. Back-flush it through the upper radiator hose. You can do it with the thermostat housing off and just go till it runs clear. Be sure to open the heater to full/hot to clean out the heater. Then just flush the radiator and overflow separately. I always do what Bish does, too. Add half the cooling system capacity with Dex and then top off with water after flushing. Oh, the block drains are those big brass hex plugs on the bottom of the block back by the transmission. I'm not sure how hard it is to get those off of there. Anybody know?
One more thing. I'll second, also, that this stuff shouldn't be left in 100K miles. Down here in AZ, the heat kills the hoses anyway so they need to be changed sooner than that.

I found that big brass plug, but I have no tool big enough to fit in there. Anybody know what size it is, so I can buy that specific size, not a set?

Also, does my 06 have a radiator drain, or do I just disconnect the lower rad hose?

LC