Flushing the Cooling System

[Jmalbright]

I have a 2004 Alero with the 3400 engine and it is time to flush and refill the cooling system. Would someone please tell the procedure to do this with one of those backflushing kits you can get from autozone? You know, the ones that have the attachment that splices into the heating hose. I'm actually not sure which hose is the heating line so if it would be possible to get a pic of it, I would appreciate that as well.

I have the Haynes repair manual, but the method they have in it for flushing the cooling system requires removing the thermostat which seems like a lot of uneeded work since autozone sells the back flushing kits that don't require removing the thermostat.

Thanks for the help.

[BNaylor]

Here is a general cooling system flushing procedure using the Prestone kit. Just to be sure to connect the tee in the right heater hose which will be the return line not pressure. Also, the air bleeder on the Alero with 3400 V6 is located on the black tower on top of the water pump. Also, there is no radiator cap on the radiator but so reference the pressure cap on the reservoir tank on the passenger side inner fender. The radiator drain is located on the driver's side of radiator front.

Install the flush T from the Prestone Flush Kit or similar in the heater return line hose from the heater core per the instructions on the label.


1. With engine cool, remove radiator cap and drain the radiator.
a. Turn drain plug (lower left engine-side of radiator) counter clockwise about 1/8 of a turn (may require a little force if it's not been opened in awhile--be careful because it's plastic). Use the end of a 1/4" drive handle. Plug will extend slightly as it loosens. Be sure to have a container in-place to collect the antifreeze.
2. Let all the antifreeze drain into a container.
3. Remove, drain and clean the antifreeze overflow bottle. Reinstall bottle.
4. Hook up a garden hose to the flush T and turn water on (Caution: not too high or you can damage seals/gaskets with the pressure). When water starts to run from the drain plug, start the engine and turn the heater on (make sure you leave the water running during this process).
5. When water runs clear (about 5 - 10 minutes), turn off car, then turn off water, and remove hose from T and cap it. Let remaining water run from drain plug. (Note: Not all of water will be drained out of system mainly the engine block. What I do is hook up a drain hose to the T connector, start engine and let the water pump push water out of the system. As soon as you see no water coming out turn engine off, remove drain hose and cap off T connector).
6. Close radiator drain plug and fill radiator with a 50-50 mix of extended life 5/150 antifreeze/distilled water (or buy premixed 50/50).
7. Start vehicle and bring to operating temperature to make sure thermostat opens. Add additional mixture as necessary until full.
8. Reinstall radiator cap.
9. Release any trapped air in cooling system by turning the plug on the top of the thermostat housing (be careful not to burn yourself). When only coolant (no air) flows from the plug, close it. You may have to repeat this several times to get all of the trapped air. Raising the front end of the car where the radiator is higher than the engine helps bleeding.
10. Add additional coolant as necessary. Also, fill overflow bottle to recommended level. Be careful not to open radiator cap if hot. You may have to do this several times.
11. Check for leaks.
12. Properly dispose of old antifreeze.

[Jmalbright]

Thanks for the response. Just to be sure, does the red arrow point to the correct hose I want to tap into?

[BNaylor]

I don't have my son's Alero to look at since it is in New York but it looks correct. The return line is the one that loops back over to the throttle body area and then over to the water pump through the black metal tubing. Pressure goes from the output of the water pump directly to the input at the heater core. When I get a chance I can double check the GM Alero factory service manual but that won't be until I get home after work.

[Jmalbright]

Originally Posted by BNaylor

I don't have my son's Alero to look at since it is in New York but it looks correct. The return line is the one that loops back over to the throttle body area and then over to the water pump through the black metal tubing. Pressure goes from the output of the water pump directly to the input at the heater core. When I get a chance I can double check the GM Alero factory service manual but that won't be until I get home after work.

That would be great if you wouldn't mind checking. I don't plan to flush the system until this weekend anyway.

Another thing, the instructions on the flush n' fill kit mention disconnecting the upper radiator hose in addition to having the radiator drain open while flushing since there is no radiator cap. I noticed that in the instructions you gave mentioned nothing about this. So, is it necessary to disconnect the upper radiator hose while doing the flush?

Finally, is there any reason to remove the engine block drain plugs during the drain or flush of the system??

[BNaylor]

Based on your pic that is the right hose which is the heater core outlet. Of the two ports you see at the firewall which go to the heater core left is outlet (return) and right is inlet (pressure).

The general instructions are for GM cars with the regulator radiator but you can improvise. It is up to you whether to disconnect the upper radiator hose or even remove the thermostat as some people do. BTW - Removing the thermostat on the 3400 engine is a PITA!

Removing the engine block drain plugs is OK if you can find and get to them but the instructions mention a way to remove most remaining coolant/water from the system by starting the engine and letting the water pump do the work. See step 5. Just to be safe make sure you run a hydrometer test of the coolant to make sure the premix is correct. 50/50 should protect down to -37 degrees F.

Good luck and let us know how it turns out.

[Jmalbright]

Thanks to all your help, I was able to get my system flushed and refilled fairly easily. I was expecting to need around 13 quarts of coolant, but only ended up using 8-9. Is this normal? I tried to get all of the water out of the system by running the engine with a drain hose as recommended, but when I was bleeding the system I noticed there was some clear water coming out, so I just bled until the remaining water was pushed out and I could see the coolant come through.

[WestMesa]

Originally Posted by BNaylor

I don't have my son's Alero

Thanks all, good info.

I may be mistaken, but there seem to be a couple of contradictions above:

#1: “The return line is the one that loops back over to the throttle body area and then over to the water pump through the black metal tubing”
Seems correct: water pump pulls coolant and pushes it to the bottom of radiator

(seems to contradict)

“Pressure goes from the output of the water pump directly to the input at the heater core”
Seems incorrect: heater is usually fed from near the thermostat

#2: “Just to be sure to connect the tee in the right heater hose which will be the return line not pressure.

The above seems to contradict the Prestone Flush & Fill Kit which says:
“2. Identify the heater inlet hose and locate a relatively straight section of the hose away from the hot exhaust system.
“3. Install the Flush & Fill

I worked up a flow diagram which I *think* is right. I just put it in a Google Doc called Alero Shop Notebook here:

https://bit.ly/3JxTbT6

Anyway, I put the flush tee in the RETURN line (the top one) because the access was easier. Not sure if it makes all the much difference.

I will put other pix here too if that would be helpful.

Thanks again