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Discussion Starter #1
Does anyone know a suitable replacement tubing for the coolant tube that runs from the thermostat housing to the overflow tank on my 1983 Shadow 750? The tube has a 7mm ID, a length of about three feet and must be extremely pliable. It is no longer offered as a replacement part by Honda and I tried all the motorcycle shops AND industrial hose supply shops in the area with no luck. Because of the heat and pressure the tube must sustain I was cautioned during my searching to use the correct tubing. I was warned of the prospect of having scalding coolant spraying on my crotch region as I rode remarkably fast. Please advise. Thanks in advance.
 

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Normally, and I am pretty sure your bike and mine are close enough, the overflow tube does not carry any pressure. It allows the fluid to be 'drained' into the over flow tank when the bike is hot and the pressure cap releases a little.

The secondary function (or primary depending on how you look at it) is to allow the cooling radiator to pull (as in vacuum) the extra overflowed anti-freeze fluid out of the overflow tank and replenish the radiator.

I don't think you could go wrong with a suitable (don't worry about the 7mm part get the closest you can in non-meteric 1/4" or 5/16") vacuum line or in a pinch fuel line (probably overkill).
 

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Considering almost every modern car has an overflow tube I can't believe the dealers couldn't help you out. I mean we're only talking 12-13 psi and 250 degrees. cbjr0256's suggestion will do fine and I'll add this link to JC Whitney. http://www.jcwhitney.com/webapp/wcs/stores/servlet/Product?storeId=10101&Pr=p_Product.CATENTRY_ID:2000882&TID=101&productId=2000882&langId=-1&catalogId=10101

Any EPDM rubber tubing should work for you. That hose will have coolant in it at all times so it must be resistant to anything in the coolant.
 

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On my 1986 VT700, the overflow nipple on the thermostat housing is between the lower housing and the pressure cap, which means that the overflow tube is carrying radiator pressure. If the tube was connected above the pressure cap seal, how would the fluid be drawn back into the radiator when things cooled down and the radiator cap was sealing correctly?

This is why my overflow tank has a gasket to seal it, and a decent clamp holding the hose on the bottom. The overflow tank is subjected to radiator pressure as well, via this hose.

So, the tube should be able to carry at least 15psi, and withstand temperatures of 250 degrees. I think fuel line would be suitable for doing that, and that's what I would use.

Please feel free to disagree with me on the fuel line, since I'm not sure what pressure and temperature it is actually rated for.

--Justin
 

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tubes_rocks

I just checked my 87 VT700 (basically the same as 86) and the overflow tube goes above the pressure cap, just like autos. I had my plastic trim pieces off so it was easier to see, if these are in place, it looks like it goes to the lower housing.
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Steve157

For replacement tubing, 7mm = .276 inch, so 1/4 ID hose will fit, if it's tight, hold the ends in hot water to soften a little, or use a blow dryer. 5/16 is around 8mm, may be more difficult to tighten.

Use fuel line - SAE 30R7 (-40 to 257 F temp, around 50 PSI or 24" Hg vacuum) or SAE 30R9 - fuel injector line (around 250 PSI, other ratings similar or better)

Any auto parts stores should carry this. I like NAPA, their hoses are all Gates Rubber, and so are their belts (good quality).

Gumpy
 

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I do stand corrected! I just went outside and checked, and sure enough, the hose is above the seal for the cap. So, in that case, how does the coolant get pulled back into the radiator when it cools down? The radiator cap seal would be blocking it from getting back into the radiator, or so it would seem to me.

--Justin
 

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tubes_rock

The overflow setup is just like a car. The cap is spring loaded (the black rubber seal), overflow goes through tube to BOTTOM of overflow tank. Upon cooldown, a vacuum is created, and there's a vacuum valve in the center of the cap pressure seal area. So, air/overflow is pushed out when hot, vacuum upon cooling draws in fluid (tube in BOTTOM of overflow tank)

Gumpy
 

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The picture is clearing up, the overflow system is there to prevent air inside the cooling system, as pressure builds below the cap, air is pushed out, into the overflow tank, the hose enters either the bottom of the tank or the exit of the hose is well below the water line, as the system below the cap cools/belches, it draws liquid back into the system, not air, the tank should be open to the atmosphere, the overflow hose doesn't hold nor does the overflow tank hold cooling system pressure, they are both open to the atmosphere, typical single ply hose and clamps will suffice...it normally takes several heating/cooling cycles to purge the system of air and the fluid level in the overflow to stabilize....my 2 cents...Mick....if you cooling system overheats and boils/steams, the pressure exits all around the cap, not just into the overflow tube.....
 

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Radiator caps are sealed both at top and bottom of the "well" in the radator fill inlet. The overflow tube goes into this "well" area. If it weren't sealed top and bottom, the system wouldn't draw in coolant from the overflow tank.

If you have a serious "boilover" out the cap as you mention, you'se got's problems!

If your cooling system - bike or car - is in proper working order, all you ever need to check is the overflow tank. Make sure you top it up with the proper mix of water/coolant. (Well, maybe pop the radiator cap once in a while, that'll let you know if your system IS in good order. OPEN ONLY WHEN COLD!!!)

Gumpy
 

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Steve157 said:
Does anyone know a suitable replacement tubing for the coolant tube that runs from the thermostat housing to the overflow tank on my 1983 Shadow 750?
You can go to www.bikebandit.com and pull your bike up. It will give you all the part numbers you need.
 

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Discussion Starter #12
I thank all of you for your replies and assistance. As advised by this forum I went to my local Honda AUTOMOBILE dealer and asked for the radiator overflow hose. The parts manager chopped off a suitable length and gave it to me free of charge. This forum is the best source of information and it is because of all of you....the members. I thank you all and send you my best. Steve
 
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