Coolant level at radiator cap

Nolan-GA

Joined
Nov 15, 2017
Messages
8
Location
Columbus, GA
Bike
2002 ST 1100
Checking my coolant level before a 3 day trip. Accessed the radiator cap. The coolant level is a about 4 inches below the cap. Should it be to the top? If so would a shop have filled it to the top when servicing? Had it serviced about 3 months ago.

Also, any advice on other things to check while i have it taken apart? Checked the brake fluid and airfilter already. About to clean battery posts. Thanks in advance.
 
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It likely won’t be all the way up to the cap when full and cold. If it’s overfilled, the overage will go to the overflow tank on the right side of the bike. As long as your coolant level in overflow is good, I wouldn’t worry too much.
 
Check the overflow tube from the tank filler cap to the reservoir, make sure it isn’t split or gummed up. If you do top it up use the Honda line coolant as it won’t damage the cooling system.
 
My guess is the shop simply checked the overflow tank, and ignored the radiator cap - unless they were removing the fairing and doing extensive work.* If there are no leaks, they would probably not check the radiator. When changing antifreeze we fill the radiator, burp the system and fill the reservoir. Three to four inches sounds low to me. I would fill it to within an inch or so of the cap, fill the overflow tank to the midpoint between the low and high level lines, and keep an eye on things. Park the bike on a clean surface and watch for leaks.

I've been using Honda Type 2 Anti Freeze (premixed with water). Costs me $20/gal at a local Honda car dealer - though I can easily pay $30 at other dealers.


* There is a reason so many guys on this site hold dealers in ahhhh low esteem. Some of this carries over to service shops, but there are good guys out there. It is our job to find them.
 
The radiator coolant level should always be right to the top of the filler neck when cold or hot. As the coolant warms up it expands and the excess is expelled from the radiator in to the overflow tank. As the coolant cools and contracts the coolant is drawn back in to the radiator from the overflow tank keeping the radiator completely full at all times. Four inches low is a lot. Make sure that you have the correct amount of coolant in the overflow tank- there needs to be a minimum amount of coolant in the tank for the system to function correctly. Make sure that you do not have a leak anywhere, including in the overflow tank and the connecting plumbing. If you can confirm that there is no leak anywhere then there was air left in the cooling system when it was serviced which has now found its way to the top of the radiator and you simply need to top it up and monitor it. If that is not the case you may have a defective radiator cap which is not allowing the expulsion/suction of coolant to and from the overflow tank to happen as it should- i.e. it is not sealing and allowing a vacuum to be created in the radiator as the coolant cools so that the coolant is drawn back in from the overflow tank.
 
After reading everything I'm considering changing all the coolant. Manual doesn't explain how to drain the fluid and i didnt see any posts here on it. Any reasons I shouldn't replace all the fluid? Where can i find instructions for it? Thanks.
 
I don't know if its specified anywhere, I don't see it in the service manual, but I've always filled mine up to the top, just below the lower part of the filler neck. And whenever I check the level, its always at that same level.
 
Honda dealer parts dept was closed. Can anyone tell me if the prestone antifreeze for Honda and Nissan or zerex Asian red antifreeze will work? Is there an ASTM# I should look for? The zerex states its ok for aluminum and is silicate free, the prestone doesn't. Have the bike apart so really wanted to fill up the radiator today if possible. Thanks again ST people.
 
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I used the red Zerex in my bike when I emptied the radiator last year and it was fine. This year I used the premixed Prestone that is silicate free when I did the hoses and the timing belt job. Any AF is fine as long as silicate free. Many use the blue Honda stuff but it’s not mandatory. What you can do when you refill is let the bike run with the cap off, make sure it’s burped of air, and fill up as much as you can up to the neck. Don’t rev the engine otherwise you’ll have coolant all over and don’t turn it off without putting the cap on first, otherwise, you’ll have coolant all over.
 
Andrew Shadow said:
The radiator coolant level should always be right to the top of the filler neck when cold or hot.
Click to expand...

Have to agree 100% on this. Before I bought it, my ST sat for 10 years with a partly drained coolant system and the radiator and thermostat/cap were not in the best of health from corrosion. I used some cold weld to fix the worst of it but always found the level to be down by an inch or so, until I finally plugged some tiny pinholes on the side of the radiator. Since then, every time I've checked, the level is 100% full. It only take a tiny air or coolant leak to allow the level to drop in the radiator.
 
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