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Discussion Starter #1
The 2008 Nomad 1600 I've ridden for the past ~8k miles spit out almost, if not all coolant through the overflow hose while idling the other day. It now has only ~18k miles on it now, for the record. I read up on how to refill and bleed the system and then did just that tonight. The fan does come on for short periods while it idled in my shop but nothing like I remember it running before. It also dribbled and would have emptied the system through the overflow hose again had I let it. No over-temp light comes on except during key-on and starting, etc. My reading up on the symptoms have now left me wondering where to start spending money and turning wrenches. Any thoughts you would like to share will be much appreciated.
 

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Blowing coolant out of recovery tank means that engine is boiling.

Run engine for a few minutes to bring up to temperature, then:

1. Touch (carefully) upper radiator tank to see if it is hot.
2. Squeeze radiator hose of your choice to see if it is soft or hard.

Post back with results.
 

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Discussion Starter #4
Blowing coolant out of recovery tank means that engine is boiling.

Run engine for a few minutes to bring up to temperature, then:

1. Touch (carefully) upper radiator tank to see if it is hot.
2. Squeeze radiator hose of your choice to see if it is soft or hard.

Post back with results.
It took approximately 10 minutes at idle (in the shop at 40 deg ambient air temp) for the coolant to begin to fill back into the overflow tank. The fan kicked on at ~11 minutes and ran for less than 2 minutes.

The upper radiator tank was too hot to touch for more than a second or so.

The radiator hoses (upper & lower radiator as well return hose from the jugs) did not seem to have changed much. They may have been a little more firm but not much.

I shut the bike off at after ~15 minutes of idling.
 

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If the engine is hot enough to turn on the fan and radiator hoses are not rock hard, then the system is not building pressure as it should.

Common causes for that are:

1. Faulty radiator cap.
2. Coolant leak somewhere in the system.

If the system cannot build pressure, it may boil.
 

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Discussion Starter #6
Thank you for the info. The cap can be replaced without much effort/cost as I already have the tank unbolted. I see no exterior leaks in hoses, radiator, etc. and do not detect anything in the exhaust. Is it a safe assumption to make that the water pump is functioning okay since it will idle that long without boiling the coolant?
 

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Discussion Starter #8
sfair - does it follow logic to think that the cap is sealing properly if the coolant does not immediately drain out when the drain plug is removed and only free-flows once the cap seal has been broken? Is it likely that the cap could hold a reasonable with no pressure when cool but leak when hot? The cap has not arrived yet but will be installed once it gets here regardless of the answers.

I apologize for the (maybe stupid) questions but I'd prefer to understand as much as I can.

Thank you once again.
 

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If the engine is hot enough to turn on the fan and radiator hoses are not rock hard, then the system is not building pressure as it should.

Common causes for that are:

1. Faulty radiator cap.
2. Coolant leak somewhere in the system.

If the system cannot build pressure, it may boil.
Agreed. First thing to check is the radiator cap. You don't want to just throw parts at a problem to diagnose it normally, but the radiator cap is a consumable and should be replaced periodically anyway, so now is as good a time as any if it has never been replaced. If a new cap does not solve the problem, a pressure check of the cooling system would be the next thing to try.

Or you could spring for this first: https://www.amazon.com/Mityvac-MV4510-Motorcycle-Cooling-System/dp/B005MVBFKQ and possibly save on the cap and certainly on the cost of having a shop do the pressure check. And who doesn't want a new toy/tool in their tool chest to start the new year? :devil2:
 

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Discussion Starter #10 (Edited)
Conclusion to the problem

1st - thank you to those who offered advice. You guys are always a big help.

2nd - I bought a new radiator cap, replaced it and the problem disappeared.

3rd - before the cap arrived, I used the opportunity to buy the cooling system test kit, so once it arrived, I tested both of the caps, old & new. The old failed to pressurize and the new held just fine.

Last - I had also decided that, since I had the tank removed and the coolant drained, it would be foolish not to replace the other consumables at this point. For ~$30 total, I bought a new thermostat and o-ring, replaced them, and put it all back together.

I'm ready for warmer weather.........

Thanks again. Hopefully this thread will help someone else down the road.
 

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2006 VN1600 Mean Streak. I had the exact same thing happen to me today. Rode for over 200 miles today with no issues, then got stuck in traffic, 90°F outside, coolant dumped out of the overflow reservoir vent tube, leaving a big ol' puddle of coolant on the road under my bike.

Looking at replacing the radiator cap and possibly thermostat since I'll be in there anyway and I know they go bad eventually if it hasn't already...so where did you find the parts for so cheap?? The OEM parts on Partzilla are $73 for the cap, t-stat, and o-ring
 
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