Need to flush my coolant system

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Tynan918

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Aug 2, 2021
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How do I flush my whole coolant system?

I know that there are drain plugs on the side of the engine to drain the water out of the engine block and there are plugs on the radiator and I can remove all the hoses, but how should I flush it out?

With a garden hose ?
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Tynan918

Royal Smart Person
Aug 2, 2021
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1. Disconnect the lower radiator hose and let everything drain.
2. Flush the radiator out with a garden hose. Gets all the junk I can out of it first.
A little bit of brown came out at first but only for a second... I used the garden hose with a high pressure gun on it.

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Tynan918

Royal Smart Person
Aug 2, 2021
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3. Hook the lower hose back up, fill the system with water and run it till it is up to temp.
4. Disconnect the lower hose, drain, re-connect, fill with water, run and repeat till the water coming out is acceptably clean.
5. Fill with alternating gallons of water and antifreeze.
Can I do this with the thermostat stuck open ?

Would it be quicker and just to leave the thermostat out and let the water run through with the engine running ?

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Bonnewagon

Rocket Powered Basset Hound
Supporting Member
Sep 18, 2009
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Yes, in fact I sometimes add a bit of dish washer soap to a cruddy system. Leave the stat off, fill it with plain water and a shot of Cascade, drive around some. Drain, flush well, until it looks clean and no soapiness. Don't let the Cascade sit too long as it eats aluminum. Might eat the water pump too. Then a new stat and fill with coolant. By the way, the block drain are a total PITA to get at, and are probably rusted solid.
 
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William

Not-quite-so-new-guy
Feb 29, 2016
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This is what I've done: If you're not sure about the functionality of the thermostat, replace it first. ... Then get a garden hose handy with an on-off handle. The engine MUST be cold to do the rest. ... Turn the heater/ac to HEAT. Remove the top radiator hose. Take the radiator cap off. Start the engine and wait until the thermostat opens. You'll know when this happens because fluid will flow from the top radiator hose. As the water in the radiator goes down, fill it with the garden hose. The colder water will close the thermostat and the flow to the top hose will stop. Keep the engine running. The thermostat will open again and the water will run out the top hose again. Fill with hose water until the thermostat closes. .... Repeat the process over and over until the water coming out the top hose is clear. Once the water is clear. Run the engine until the thermostat closes again. Shut the car off. Re-attach the top hose. Unattach the bottom hose and drain the radiator completely. Once drained, re-attach the bottom hose, then fill the radiator with 100% antifreeze. Put the radiator cap back on. Start the engine and let it run for a while. ... It's been my experience that by doing this, it will flush the entire system better than using any fancy aftermarket flush kit (which basically does the exact same thing). All things being equal, this will also result in a 50/50 antifreeze/water mix when you're done. ... If any of this makes you nervous, do NOT do it.
 
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Tynan918

Royal Smart Person
Aug 2, 2021
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I'm thinking because the radiator water was clear almost immediately when I had the water hose in it and the bottom radiator hose off that maybe the rust is coming from my heater core and I should also flush that as well.. I watched this video of this guy doing this and I'm going to use his route.

But in order for me to buy the right transparent hoses, I need to know what size these inlet and outlet heater core hoses are..

IMG_20220902_165734464.jpg
 

Bonnewagon

Rocket Powered Basset Hound
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No need for clear hoses. Just undo them and jam a garden hose against the open end and flush away. Both directions.They are 5/8" and 3/4".
 
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DRIVEN

Geezer
Apr 25, 2009
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I'm thinking because the radiator water was clear almost immediately when I had the water hose in it and the bottom radiator hose off that maybe the rust is coming from my heater core and I should also flush that as well.. I watched this video of this guy doing this and I'm going to use his route.

But in order for me to buy the right transparent hoses, I need to know what size these inlet and outlet heater core hoses are..

View attachment 206068
Those Chrisfix vids are pretty helpful but he doesn't always link other relevant tutorials. The clear hoses aren't absolutely necessarily needed but let you see that the rust is gone. If you don't get all the rust out it can lead to further issues. Looks like your stuck open thermostat is canary in the coal mine.
 
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Tynan918

Royal Smart Person
Aug 2, 2021
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This is what I've done: If you're not sure about the functionality of the thermostat, replace it first. ... Then get a garden hose handy with an on-off handle. The engine MUST be cold to do the rest. ... Turn the heater/ac to HEAT. Remove the top radiator hose. Take the radiator cap off. Start the engine and wait until the thermostat opens. You'll know when this happens because fluid will flow from the top radiator hose. As the water in the radiator goes down, fill it with the garden hose. The colder water will close the thermostat and the flow to the top hose will stop. Keep the engine running. The thermostat will open again and the water will run out the top hose again. Fill with hose water until the thermostat closes. .... Repeat the process over and over until the water coming out the top hose is clear. Once the water is clear. Run the engine until the thermostat closes again. Shut the car off. Re-attach the top hose. Unattach the bottom hose and drain the radiator completely. Once drained, re-attach the bottom hose, then fill the radiator with 100% antifreeze. Put the radiator cap back on. Start the engine and let it run for a while. ... It's been my experience that by doing this, it will flush the entire system better than using any fancy aftermarket flush kit (which basically does the exact same thing). All things being equal, this will also result in a 50/50 antifreeze/water mix when you're done. ... If any of this makes you nervous, do NOT do it.
Can't I do this or another procedure to flush the engine block out, without a thermostat in the intake ?

Won't have funds for a few days to buy a thermostat and I want to get this coolant system flushed and filled ASAP... Radiator and heater core are flushed and running clear, now I just need to flush the engine rusty water out.
 

403Olds

G-Body Guru
May 31, 2014
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The garden hose flush for the radiator and block is what I do, flush till it comes out clear, find the coolant capacity of the cooling system, put in half that amount in full strength coolant, then top off with water. For winter cars, I've had good luck flushing the heater core both ways with a garden hose. Had a Buick Roadmaster that I had to do that about every year, then I'd get good heat all winter.
 
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