Where Should the Expansion Tank Go?

I got to thinkin'.

I just installed my K&N filter extravaganza. Three for the throttle body, one for the crankcase, and one for the air temp sensor. They're all in their places with bright, shiny faces. I was also able to install the bearclaw without modification. I now have a big, empty airbox under the seat. I know that some folks use this empty space to relocate the cooling system expansion "bottle."

As I look at it on my '08 R3T, I notice that the stock location for the expansion jug is to have the bottom of the jug above the top of the radiator. I also remember every freshwater-cooled boat motor I had doing the same thing. If I relocate the expansion bottle into the empty airbox, won't the bottle overflow since the bottle would be below the top level of the rest of the cooling system?

Since I'm able to get the BC on without hassle, it's really just a question for curiosity's sake. It may, however, be good to relocate the bottle to improve airflow around the throttle bodies.

It's open season - take a shot.

Had a cylinder made up and bolted to the lhs downtube, by the sidepanel.

I've had mine in the airbox for a year or two, probably 8k miles or so, no problems at all. Moving it will get you some better airflow, but only really makes a difference if you remove the windshield lowers. With them in place you have a big pocket of still air in front of the filters. I noticed a big drop in intake air temps when I took those lowers off. Of course, you get more airflow and some buffeting. Not a problem in warmer temps, but not great in the winter. Guess there is no free lunch after all.

Since the seat bolts on using the box for storage on the R3T isn't really a good option, not to mention that you have those big ol saddlebags sitting back there.

I have my coolant (aftermarket) recovery bottle in the airbox as well. Other than dropping a needle from a large marinating syringe into it; it works well.

Dunno if it fits the same in the 'T' but in the standard/classic, you can get it to fit behind the left side panel. Just swap the hoses around .

Thanks for all your responses.

I can't figure out how the bottle doesn't overflow when it is below the top of the radiator. That's got me stumped. I believe you guys when you say you have it mounted in the airbox, but I keep imagining that every time it gets hot enough, the box fills with green, gooey coolant. As I remember it, my '86 Kawa 1300 V-ger had the expansion tank mounted low on the bottom of the frame. I also remember that you had to do some fancy heat cycle thing to get the airlocks out of the coolant system when you changed the coolant because of that location. I suppose you'd have to do something similar if the bottle was mounted in the airbox or, like The Feathered One, low on the frame.

Harry, what's the practical effect of having the air temp sensor reading a lower temp after you remove the lowers and get more direct airflow? Do you have to adjust the tune map or anything else? Does it mess with fuel milage one way or the other? My guess is that cooler, denser air would fatten the mixture up a little. I can see the effects of direct airflow acting on the front throttle body much differently than on the rear one. I can also see the direct airflowm being affected more dramatically with variations in speed. It all smells like adventures in re-mapping to me. And you can't compensate for the full effect of the changes brought on by varying airflow in a dyno booth. You'd be guessing. I only want to do the dyno thing once (they charge $3000/shot), so I'd like it set up to where it'll stay put for a while.

bb, the left side panel is stuffed full of evap cannister. And whatever room may be left, I was hoping to cram in a stebel horn air compressor. It would be nice to get rid of the evap crap and have it gone for good, but in all the posts I've read about mods and stuff, I don't recall anyone doing that. They just leave it alone and let the computer work around it. I could be wrong on that.

Here's a couple of pics of mine (worth a thousand words?)



You can see it bolted to the downtube on this one - lower than the original bottle. Had no trouble since I fitted it last year.

I was a little worried about it overflowing when I put it under the seat too.
So to eliminate the possibility, I made mine out of an old metal canteen,
screw on top, heliarked tubes into aluminum canteen.
Now it'll pressure-up and NOT leak.

The vacuum created by the radiator keeps the bottle from overflowing. The small amount in the tubing is not enough to cause an overflow when you open the rad cap. Remember, when the rad cools after shut down, it sucks fluid back through the hose into the rad as long as you don't have any bubbles in the hose.

I've had my chrome recovery bottle mounted to the crash bars. When installing, hook up the hoses and raise the bottle above the rad to remove all air from the line. I use clear tubing so that I can see. Once the line is bubble-free, I lower the can and attach it to the crash bar. If all the hoses are tight, it maintains a solid block of fluid.

I put mine behind the L/H sidecover.