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I finally got around to doing the coolant change on my 2015 GTS 300. It's been about two years since the last coolant change, which was done by the dealer. I initially stripped the screws trying to remove the water pump cover, so I decided just to remove the hose and replace the one-use clip with a stainless steel reusable clip. The water pump cover gasket isn't leaking, so I'll deal with the stripped screws on it another time. Pretty much everything went smoothly until it came time to bleed the system. Instead of having the forethought to reuse the coolant that was bleeding out of the bleeder valve, I had it drain into the same container as the old coolant. I won't make that mistake next time. So, even though I had well over a liter on hand, I ran a little short. I was probably about 60ml or so short... So I used some distilled water (which I swirled around the empty coolant containers to pick up the residual coolant left over). So, here are my questions:

1. Is the addition of that that small amount of distilled water (about 60ml or 2 ounces) acceptable? Or do I need to redo the entire process?

2. How do I know if the "bleed" was successful? The bike seems to be running fine, but is there some other indication? If there is too much air after I bleed the brakes, they are "squishy", so I know I need to bleed the brake lines more more. Anyway to know about the coolant bleed? What happens if there is air in the coolant?

Thanks again everone.
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From what I know, if there was air it was expelled when it passed into the expansion tank; this is because, differently from the brake circuit which must be under pressure, the cooling liquid does have to have a steam outlet which is formed when the engine is too hot.
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@miguel avatar
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Good on you for taking that simple but messy job on. Probably no problem with 2 oz water. But you could get more coolant and save the remainder for the next change. Its cold in Connecticut and you don't want the coolant to freeze when its 20 below for days on end.

Also, did you let the bike idle after initial filling nnd open the bleed screw on the engine after you started the engine? If not you probably have air in the system and need to go back and do that. When you retighten the bleed screw, be careful. It doesn't need much but you don't water to strip the threads on the bleeder.

Lastly, let it idle on the center stand and make sure the fan comes after it warms up, just to make sure the fan works. Takes about 10 minutes to reach temperature. Then, check the coolant level one more time.

If you haven't watched them, watch either or both the McBergsma and scooterwest coolant change youtube videos. They are both excellent.

Hope that helps.

Miguel
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Problem
Usually air trapped in the system will result in the engine running too hot, as the air interferes with coolant circulation. If your temp gauge indicates proper temp, you got enough of the air out of the system for it to function properly. Usually coolant systems will self-purge the air over time, as the system is repeatedly heated and cooled. Just watch the expansion tank for coolant level.

The addition of water will raise the freezing temperature of the coolant somewhat. If you are OCD (like me) you can probably find a table somewhere showing the freezing temp for various proportions of water/coolant. So you'll be able to predict if it is going to be a problem in your locale. It will also slightly reduce the proportion of anti-corrosion chemicals, but probably not enough to be a problem.

FWIW, I'd probably have used some of the old (filtered) coolant, rather than added distilled water. While it loses the anti-corrosion properties over time, the 'anti-freeze' part still works.
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Hi theschuman, great job I'd say! I wouldn't stress too much about being slightly short of coolant mix in there, but I'd probably buy some more of your coolant (same brand and type) and put just a glug in the expansion tank. You can take out some fluid from the tank with a turkey basters or some such device first and then just top off with 50-60ml. It's not really too much about the freezing point as you have probably got enough freeze protection depending where you live, but it's more about the water pump lubrication. A 50/50 mix is designed to give best lubrication to the seals and make them last longer. A diluted mixture isn't as good.

I wouldn't mess with putting in any of the old coolant. It'll already be going acidic and will accelerate deterioration of the new stuff even though it's only 60ml.

Regarding any trapped air. The GTS250/300 bikes don't self bleed like the 200's do (mostly). So getting all the air out is important. Best way is to hook up a transparent plastic tube so you can see the fluid coming out of the bleed screw. You can also see the air coming out quite freely. You need to make sure the bike is warmed up first so the thermostat is open. Let the bike idle, when warmed up simple connect the tube to the bleeder and open the screw and watch to see what comes out. You don't need the screw open much. When you think you've seen the last of the bubbles, turn the screw closed (finger tight plus 1/10th of a turn). It seals with a rubber O ring inside, not from the pressure exerted on the bleed hole.

Do the procedure above at least three times, revving the engine slightly each time to drive the coolant around the system faster and move any air bubbles into the thermostat housing. then rebleed again.
⚠️ Last edited by Stromrider on UTC; edited 3 times
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If you're worried about freezing the motor in a Conn. winter, you can go to an auto pats store and buy a low cost coolant tester. After a couple weeks of riding, test the coolant in the reservoir tank. This should give you some piece of mind.
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Thanks everyone. I did bleed the system when I did the coolant change. I reved the engine per the instructions in the Haynes manual, coolant came out... Air bubbles stopped coming out at the bottom of the hose, but where the hose meets the bleeder nipple, I always seem to get some tiny bubbles. It happens to me when I do brake fluid changes, too. I always try to use a tight hose and sometimes use heavy grease around where the hose meets the nipple. I still get little "micro bubbles" at the bleed nipple, but then all fluid (and no bubbles) at the end of the hose when I'm finished. The brakes are then tight, so I think i'm getting the air out.

I think the coolant change went well. So far, I've driven at least 50 miles with no issues and no temperature warning light (I have no temperature gauge). I'll get some more Eni Ezpecial and add it later with the "turkey baster" method. Great ideas everyone! Thanks again.
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Also mine is missing a temperature indicator, there is only the red boiling light; next step would be to install a yellow LED to indicate the reached operating temperature and a buzzer in parallel with the red light.
Is there an electronic engineer on the forum who has to publish a circuit diagram with a probe and trimmer to calibrate at the right temperature?
⬆️    About 1 month elapsed    ⬇️
OP
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When I did my coolant change back in October, I ran out of the OEM (Eni) coolant and added some distilled water to the Eni pre-mixed coolant. I finally had time to extract some of this distilled water/OEM coolant mix and replace it with more of the Eni pre-mixed coolant. I used a syringe to remove quite a bit (about 750ml) of the distilled water/coolant mix and replaced it with 750ml of fresh Eni coolant. Do I need to re-bleed the system?
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If you removed coolant from the reservoir you shouldn't need to bleed the system. The rest of the coolant remains in the radiator, pump, and hoses.
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Theschuman, 60mL water is only 3% of the 2L capacity of the cooling system. I suspect that when eni makes the stuff, there is probably that much potential error in the concentration anyway. So I wouldn't worry about it too much in future.
Cheers, Jim.
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