The Mystery of the Disappearing Coolant
 

I keep refilling the coolant overflow bottle on my RX3, but it never stays full. How is the coolant disappearing? :wtf:

All motorcycle engines with water cooling have an small hole near the water pump which will ooze coolant if the water seal fails. I have repeatedly examined this inspection hole on the RX3 water pump, and it is not leaking coolant. Therefore, I must believe the water seal is in good condition.

I have also checked all the hoses and connections between the engine and the radiators. I have not discovered any leaks.

How is the coolant disappearing? I certainly think any air voids in the coolant system should have been filled by now. I have recorded over 8,000 miles on the odometer of my RX3 motorcycle. :shrug:

8000 miles ... you are my hero :clap:

As to the coolant ... could it be leaking inside the engine somehow? How's the oil level, smell and color?

How much and how often are you needing to add coolant? Is the overflow bottle vented, could it be evaporation that could happen very quickly with the heated coolant. Is it possible to temporarily block off the overflow bottle so you have a completely sealed system. Then ride for a week as usual and see if you lose any coolant. Just an idea, don't know if it will work.


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The oil level remains constant. At every oil change the used oil is in excellent condition. :tup:

The coolant disappears slowly, so I don't suspect faulty gaskets. At first, I thought the left radiator had an air void from the factory, which needed to be refilled. However, after refilling the coolant overflow bottle many times, I now suspect Adjuster is correct. ;)

If it's evaporating ... is your coolant getting more concentrated? or do you think the coolant evaporates along with the water?

The coolant overflow bottle is rather small, and I only need to add a small amount of coolant every two weeks. The coolant overflow bottle is not vented, but the cap does not tighten securely as it does on my Honda CRF250X. Therefore, I suspect you are correct, and the heated coolant is slowly evaporating over a span of several weeks. ;)

I could plug the tube to the coolant overflow bottle, but I don't think that's a good idea. ;) The cooling system is working superbly, and my engine never overheats. Every time I remove the radiator cap, the coolant level is full to the top of the radiator. :) Therefore, I suspect evaporation is the problem. ;)

I am willing to accept slow evaporation from the coolant overflow bottle as a minor quirk of the Zongshen RX3. ;)

I haven't studied this issue, but I suspect a 50/50 mix of ethylene glycol maintains the same concentration as it evaporates. :shrug:

http://www.researchgate.net/publicat...liquid_mixture

Also, the suspected evaporation occurs very slowly, over a span of several weeks. Therefore, I don't think the coolant in the overflow bottle is becoming concentrated. ;)

According to the following thread, if the coolant overflow bottle does not hold pressure, the coolant will evaporate. ;)

http://www.bobistheoilguy.com/forums...Number=1600370

I seriously doubt the coolant overflow bottle of my RX3 motorcycle can retain pressure. If I tighten the cap too much, it releases. :wtf: Did I get a bad coolant overflow bottle? Does the cap tighten securely for others?

The following threads also support the theory that an unpressurized, coolant overflow bottle will allow coolant to evaporate. Is my coolant overflow bottle defective, or do all the RX3 bottle caps refuse to tighten securely?

http://www.jk-forum.com/forums/stock...normal-137010/
http://forums.nasioc.com/forums/show....php?t=1467927
http://honda-tech.com/tech-misc-15/n...-tank-2880706/
http://www.subaruoutback.org/forums/...ed-normal.html

I thought overflow caps weren't supposed to seal well. They need to vent air in and out as the overflow level rises and falls with engine temperature. However, the radiator cap must seal to force expansion into the overflow bottle and suck fluid back in. And the overflow level must stay above the fill tube to prevent air from being sucked in from there.

Any white smoke at idle?

I also noticed my coolant bottle was low a week or so ago, and filled it to the "top" mark, and it also seems to be gradually dropping. Like Spud I am beginning to wonder where the coolant is going. I don't accept the "evaporation" theory, since none of my other bikes (or cars) with non-pressurized expansion bottles loose coolant at anything like this rate.

I am not seeing (or smelling) any sign of a bad hose connection or other "outside" leak.

One possibility is that there is a head gasket leak allowing coolant to enter the cylinder, but this sometimes results in hard starting and other running problems, which I am not experiencing.

My plan is to let the coolant drop in the bottle, and then to start checking the radiator cap (engine cold of course) to see if the coolant level there also begins to drop. If it does, further diagnosis may be in order.

My bike also experiences a small amount of coolant loss over time.
I suspect an inherent design and not a problem because there appears to be a few bikes with this going on.

I filled my radiator and overflow during my valve adjustment a couple of weeks ago. But when I looked just now, it was empty. Filled it and we'll see if it drops again.

Leaking coolant is usually pretty easy to smell. And you would definitely see it if it was going into the oil. Remove your oil fill cap and examine the cap for small droplets of condensated water. You would of course also see this water in the crankcase vent tube.