Steaming x

After putting in a new piston and reassembling my bike, I now have steam coming up from the right side radiator. There doesn't appear to be a leak, as the entire radiator steams up within a a couple minutes of starting the bike. Thanks for your help!


Need more info friend. Are you sure it's steam and not smoke coming off an exhaust headed installed with oily hands? Did you make sure the over flow/reservoir line is attached? Rad cap on securly? Cooling system full?

currently Im with him^^^ Most likely is oil or grease being burned off, but you will need to look into it more.

The radiator is full (twice drained, replaced and burped). The head is clean and the radiator is clean. Lots o steam coming up. I am wondering if I somehow blocked a coolant line inside the engine or didn't replace a part between the cylinder and base.

I'm trying to put myself in your shoes. If it was my bike, I would start it up cold with the rad cap off and watch it to see if anything weird is going on (bubbles in the radiator etc.) I would also pressure test the cooling system to see if it holds constant pressure. If you're seeing steam, there's a leak somewhere, or your rad cap is shot. Just throwin' stuff out there. The top-end gaskets are pretty much imposible to have in backwards or upside down.

most likely what cc rider said, oil coming off the exhaust


It's not grease or is steam and it looks like it is coming up from the entire front side of the radiator. It also could possibly be only coming up from the bottom, since the steam rises and comes up the front of the radiator. No liquid coolant traces can be seen, just a large amount of steam. The radiator has been squished on the right side (the furthest right column), but it worked fine last year and this problem just came up after reassembling the entire cylinder.

Could I have left a part out of the cylinder/crank connection that as a result restricts the flow of coolant? Or is it a damaged radiator? If you had this problem, please let me know what the solution is.


Auto parts stores sell UV leak detection kits for about $20. Comes with a little bottle of UV dye and a flashlight that puts out UV light. Put in about a 1/2 teaspoon of dye (it doesn't take much), start the bike, turn out the lights in the shop, and look for where it starts glowing neon. There's your leak. Works great.

Also, once you have the UV flashlight, bottles of dye are only about $7 and one bottle will do one car, or a bunch of bikes. They make dye bottles for your coolant, oil, auto transmission fluid, differential, AC, just about everything.

If you are convinced that you have a coolant leak, but can't find it, try this.


Thanks for this. I just did the UV leak test as you suggested (very clever!). The only thing that showed up was a very, very small (smaller than the head of a pin) UV light return near the top left side of the radiator. I could also see the dye in the overflow tank...and on my finger. In the dark, I could also see my head pipe glowing a dull, dark red, even though I was running at a fast idle. This tells me I've got an overheating problem and now, I really doubt that I have a radiator leak. The steam comes from all over the front of the radiator and the aluminum is showing signs of discoloration over about 1/3 of the fins from what looks like overheating.

My next step is to take the cylinder off and see if I missed putting in what is called a Water Pass Collar, which fits on the bottom of the cylinder. Somehow I think I forgot to put that in and the water isn't fully circulating through the engine. Stay tuned, as I will eventually solve this and post the solution for someone else to benefit from.

OK, how long are you letting the bike idle before it starts steaming? These bikes are not designed to idle for very long without air moving through the radiators. That's why you will steam them in tight singletrack sometimes. That dull red header pipe is normal, you just don't usually see it in the daylight. If you are going to idle it for very long, you need to set up a shop fan blowing through the radiators. Remember, these aren't cars that have fans pulling air through the radiators, they depend on motion for airflow.

Water Pass Collar??? Where did you hear about that? There's nothing between the cylinder and the crankcase except the base gasket. Same thing for the head to cylinder gasket. Whoever told you about that collar, have them describe it for you and then find the part on the OEM parts diagrams. Just make sure that you are hunting a real part before you tear the thing apart again.

Are you losing coolant? Is it blowing it into your catch tank and filling it? If you are not losing coolant, go ride it (or set up fans for the rads) and see if it still steams. If you are losing coolant you have to find out where it is going. There are only two places coolant can go. It is leaking out somewhere, or it is disappearing through the combustion chamber. Now that the dye is in the system, pull the spark plug. If the end of the plug glows, guess where your coolant is going? I'm not sure, but I think that dye will still show up after going through the combustion chamber. You should be able to smell the burned antifreeze if you are burning it, too.

Dumb question, but you did use a new head and base gaskets when you re-assembled, right?


I'm also guessing you're letting it idle too long. Isn't long after its warmed up that they overheat without forward momentum pushing air through the radiator....or a fan. But when I did that with mine once, I heard it bubbling in the wasn't steaming off the rads.


New gaskets. A top flight mechanic I know thinks the pinhole is large enough to be causing the steaming problem (I have had the bike 5 years and this steam is normally can idle all day with no steam). I plugged the pin hole with solder and covered that with epoxy. Still have to test it to see if steam is gone.

The Honda parts fiche lists the Water Passthough collar, but you are right, there's no place for it to go on the bike (on my Athena 280 cylinder anyway). And the Honda Service Manual makes no mention of the collar nor does it show it. Odd conflict in the documents. I know it is not the problem.

Will confirm after I test it warmed up. Thanks for the valuable insights.

Well...hope thats it but you said the pinhole was in the left side and steam coming off the right. Perhaps its squirting over there but I'd think you could see something this obvious.

Pretty clearly a pinhole isn't a good thing, so at worst, you have one less problem.

The UV dye spot around the pinhole should b getting bigger if that is where its leaking. Where on the parts fiche are you looking for that passthrough collar? I sure don't see it.

The water pass collar fits in the right crankcase cover, not under the cylinder. You may have left it out, but you'd then find water leaking into the crankcase and have very serious engine trouble.

OK, found it. If all you did was the top end, you never would have messed with that. Only if you had removed the right crankcase cover for some reason, then like ramz said you would have water in the crankcase.

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