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Tutorial: How to drain the cooling system

Bskicrash1

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I searched the forum and didn’t see a how to. This is a relatively simple task, however, for a first timer, it is always nice seeing a how to.

I have a 2019 NC750x manual transmission. I’m draining the cooling system with just over 5k miles. I’m using Honda hp2 coolant as per the manual.

You will need 2 quarts of coolant (I use 3 quarts and I’ll explain), 1 gallon of distilled water, 5mm hex wrench, 10mm socket, 12 mm socket, JIS #2 screwdriver tip (a #2 Phillips head will work, just apply even pressure as not to strip the screw head), a funnel.

DISCLAIMER: the process described below will not remove the residual coolant that is trapped by the thermostat. There is possibly .25 quarts of coolant that will not drain out using the method below. If completely changing to a new brand and type of coolant, remove the thermostat housing to fully drain and flush the old coolant.
PROCEED AT YOUR OWN RISK. I am no way responsible for your actions.

1. Remove the lower cowl. Use the 5mm hex wrench for this. (I didn’t take a photo of this step as I forgot).

2. Locate the 10mm bolt under the motorcycle just rearward of the header pipe. This bolt has a copper crush washer, so be careful not to lose this when draining. Mine stuck to the engine then dropped into the catch pan and I ended up fishing it out. 42EAAA07-A829-452B-B889-10B57B69899F.jpeg
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3. The cap is held secure by a #2 JIS screw. This is to prevent the cap being spun off. Carefully remove this screw and then remove the cap. The coolant will now flow fast.

FECAB4CF-8CDD-446C-B957-E65632C751B5.jpeg


4. Locate the bracket that holds the horn assembly and coolant overflow tank. Use a 10 mm wrench to remove the reservoir from the bracket.
9F4DCE7F-3C94-49A9-A70C-E8C39CA0816B.jpeg

5. Use a 12 mm wrench or socket to then loosen the two bolts holding the bracket to the frame. I do not remove the bolts, I just loosen them enough so I can move the reservoir from behind the frame and drain the contents. (Caution, the oxygen sensor wire runs through a tab on the frame and around the reservoir. Use caution separating the wire before moving the reservoir.
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6. Carefully tip the reservoir to drain the coolant.

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7. Use a funnel and pour distilled water into the coolant reservoir and flush the old coolant residue out. Reinstall the reservoir in reverse order. Pay attention to the two rubber hoses as they are routed through tabs on the tabs on the reservoir.
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8. Use a funnel in the radiator and pour approximately 1/2 gallon of distilled water into the system. If you look, the color of the fluid draining from the drain bolt will change to clear.

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9. Then reinstall the drain bolt hand tight. I pour approximately 3/4 a quart of the new coolant into the system.

10. Then remove the coolant drain bolt and watch the color of the fluid go from clear to the blue of the Honda coolant. This is to ensure I do not have extra water in the system.

11. Then reinstall the drain bolt.

12. Fill the radiator and the coolant reservoir. This takes about 1.25 quarts of fluid.

13. Reinstall the radiator cap.

14. Start the motorcycle and let it heat up to operating temperature. I wait until the radiator fan turns on to ensure the thermostat opens and lets any air trapped in the system pass to the radiator.

15. Once the motorcycle is completely cooled. Open the radiator cap and top off with coolant. Also, check the reservoir and make sure the coolant level is between the low and high mark. If not, add coolant to the proper level.

16. Reinstall the lower cowl.

When I started this process, it was 20F. The frost on the motorcycle is visible.

Enjoy!
 

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bigbird

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Great write-up and pics.

I like your idea of trying to totally flush the cooling system with the distilled water and then displacing that distilled water with the fresh coolant.

However, the 0.25 qt of residual coolant is hidden away in the water pump and cylinder head cooling passages, and is undrainable without total engine disassembly.
Just pouring distilled water into the rad will not purge the "hidden" coolant.
You are basically rinsing out the rad and lower engine block by adding the water and then just draining it out again.
Unless you start and run the engine long enough to open the thermostat to circulate that water and then again after draining the water and adding the initial new coolant I don't think it will accomplish much.

The same thing occurs during an oil change.
On changing the oil and filter on a manual trans NC750, the replacement oil volume is 3.6 qt of oil.
On engine disassembly, the replacement oil volume is 3.9 qt.
That 0.3 qt is always left behind at each oil change.
 

Bskicrash1

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bigbird, you are absolutely correct! You speak good information that I didn’t even think to mention. And you are 100% correct that without disassembly, there will be coolant in the passages.

If I was completely changing to a different type of coolant, my method described would NOT be sufficient. Mixing different chemical compound coolants is not good for it will result in gumming and gelling.

I will edit the post with a disclaimer.

I also changed the title of the post to DRAIN instead of FLUSH.
Thank you, I do appreciate the input!
 
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Jt105

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I suppose you could lean the bike to the left and to the right to try to get more fluid out. In reality, it isn't needed. The little bit of old fluid will mix just fine with the new.
 

bigbird

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I suppose you could lean the bike to the left and to the right to try to get more fluid out. In reality, it isn't needed. The little bit of old fluid will mix just fine with the new.
I did that on changing coolant on my Goldwing.
I got approx another 0.3 litre to 0.4 litre out.
But the 'Wing has 2 radiators on opposite sides, so that could be a reason.
I agree, the little bit of coolant left in an NC is inconsequential IMHO.
 

davidc83

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and I wont mention my 2007 Suzuki C50 Boulevard (bought new in 2007) with 104,000+ miles with original coolant....(yea yea I know,,,the Oem Brake fluid wasnt changed until 102,000 miles)...it is my test bike on how long a bike can go with minimum maintenance other then oil and rear differential fluid changes (those get changed every 3000-5000 miles).
 

670cc

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and I wont mention my 2007 Suzuki C50 Boulevard (bought new in 2007) with 104,000+ miles with original coolant....(yea yea I know,,,the Oem Brake fluid wasnt changed until 102,000 miles)...it is my test bike on how long a bike can go with minimum maintenance other then oil and rear differential fluid changes (those get changed every 3000-5000 miles).

Rear differential? Is your Suzuki a trike?

”The differential is a device that splits the engine torque two ways, allowing each output to spin at a different speed.”

I hear the term differential used often referring to the Goldwing final drive gear box. I don’t mean to pick on you personally, but it irks me when a motorcyle shaft driven final drive is called a differential because a differential gear set has no purpose or application in a drive for a single rear wheel.

Differential gear, providing power transfer to two output shafts, while allowing the shafts to rotate at different speeds:

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TheIronWarrior

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Rear differential? Is your Suzuki a trike?

”The differential is a device that splits the engine torque two ways, allowing each output to spin at a different speed.”

I hear the term differential used often referring to the Goldwing final drive gear box. I don’t mean to pick on you personally, but it irks me when a motorcyle shaft driven final drive is called a differential because a differential gear set has no purpose or application in a drive for a single rear wheel.

Differential gear, providing power transfer to two output shafts, while allowing the shafts to rotate at different speeds:
I had the same thought, though my quick research suggests Suzuki does use the nomenclature "differential" even though it is not a true differential.
I'm assuming inside the case you'd find a ring gear and a pinion gear that resemble those found in a true diff.
 

670cc

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I had the same thought, though my quick research suggests Suzuki does use the nomenclature "differential" even though it is not a true differential.
I'm assuming inside the case you'd find a ring gear and a pinion gear that resemble those found in a true diff.
Yep. The motorcycle final drive sorta resembles a differential but is missing a lot of parts and performs no differential function.

It’s good that Honda refers to the final drive gear case as “final driven gear”.
C7C26EBD-B2DA-45BD-9465-9AE9FF30FAEF.jpeg
 
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Bskicrash1

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Did you use a new crush washer on the drain bolt? :)
I reused the original crush washer.

I did try to purchase a new one from the Honda dealer, and was not in stock. The mechanic I spoke with said the crush washer was ok to be used for several uses unless there was noticeable damage to the washer. In my case, there was not.
 

bigbird

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If the crush washer looks unuseable due to being “crushed”, just anneal it.
Heat it to cherry red with a propane torch while holding the washer in a needle nose pliers.
After heating, just lay the washer on the concrete floor to cool.
Do NOT quench the hot washer in cold water to cool it down.
That will make the copper too brittle and it will crack when tightening the drain bolt down.
You can anneal copper many times.
 

Giuseppe

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If the crush washer looks unuseable due to being “crushed”, just anneal it.
Heat it to cherry red with a propane torch while holding the washer in a needle nose pliers.
After heating, just lay the washer on the concrete floor to cool.
Do NOT quench the hot washer in cold water to cool it down.
That will make the copper too brittle and it will crack when tightening the drain bolt down.
You can anneal copper many times.
exactly what I do, I always keep a newly annealed washer as a spare along with an extra drain bolt.
 
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