The Mystery of the Disappearing Coolant

[AZRider]

Have you checked the water pump for leakage?

[SpudRider]

Originally Posted by Weldangrind

Any white smoke at idle?

No, non whatsoever. The bike runs great, and the cooling system operates wonderfully.

[SpudRider]

Originally Posted by detours

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.

The cap on the coolant overflow bottle for my Honda CRF250X seals very well. As stated in the threads to which I linked in post #9, some coolant overflow bottles are pressurized, and others are not. It appears the non-pressurized, coolant overflow bottles are prone to evaporation.

[SpudRider]

Originally Posted by NoVa Rider

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.

The threads to which I linked in post #9 support the evaporation theory. Also, I always remove the radiator cap and check the coolant level in the radiator before I refill the coolant overflow bottle. The first few times I checked, the coolant level in the radiator was down a little. However, the coolant level in the radiator has now stabilized at full level, while the coolant overflow bottle continues to require a periodic refill. However, the slowly dropping level of coolant in the overflow bottle does seem to support the evaporation theory.

[SpudRider]

Originally Posted by AZRider

Have you checked the water pump for leakage?

Yes, I did. As I stated in post #1, 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.

[SpudRider]

Originally Posted by Adjuster

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.

I don't have any coolant leaks. The cooling system works superbly. The used engine oil is always in good condition, without any contaminants. I am not collecting any contaminants in the dump tube from my crankcase vent.

I believe the left radiator probably had a small air pocket when I received the bike. I also believe the coolant overflow bottle has now completely filled both radiators with coolant. The coolant level in the radiators has stabilized at the full level. However, the coolant overflow bottle continues to lose coolant, but at a much reduced rate. Therefore, at this point, I am inclined to believe the evaporation theory.

Will others please report if the cap on your coolant overflow bottle is somewhat loose, and will not tighten fully?

[SpudRider]

Originally Posted by NoVa Rider

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 suspect you have a small air bubble in the left radiator. Keep filling the coolant overflow bottle. The air void will disappear, and the coolant level in the radiator should stabilize. After that point the coolant level in the overflow bottle should begin to drop at a much slower rate.

Please remember, I have now recorded about 8,250 miles on the odometer of my RX3. Therefore, I had ridden enough miles to fill the coolant in the left radiator. The coolant level in my radiators has now stabilized at full. Nevertheless, the coolant level in the overflow bottle continues to fall, but at a much reduced rate.

[katflap]

To me it seems counterintuitive to fill up your over flow bottle.
I'm not convinced that it can "top up" the coolant system.

If the bike were to over heat and blow, I want super hot coolant in the bottle not on me
so I leave mine empty so there's plenty of room

But that's just me

[Weldangrind]

Originally Posted by SpudRider

No, non whatsoever. The bike runs great, and the cooling system operates wonderfully.

Excellent. Any evidence of milkshake on the underside of the oil filler cap?

[SpudRider]

Originally Posted by Weldangrind

Excellent. Any evidence of milkshake on the underside of the oil filler cap?

I just changed the engine oil several days ago, when I passed 8,000 miles on the odometer. No, I did not notice any 'milkshake' on the underside of the oil filler cap. The bike runs cool, the engine runs great, the used engine oil looks wonderful, et cetera. I can't find any coolant leaks, and I don't believe the engine is consuming any coolant.

[SpudRider]

Originally Posted by katflap

To me it seems counterintuitive to fill up your over flow bottle.
I'm not convinced that it can "top up" the coolant system.

If the bike were to over heat and blow, I want super hot coolant in the bottle not on me
so I leave mine empty so there's plenty of room

But that's just me

You have an interesting perspective on this matter. As always, thanks for your input, Kat.

I do know the overflow bottle will top off the radiators on my Honda CRF250X. If the overflow bottle can't top off the radiators, why do the manufacturers always tell you to fill the overflow bottle with a certain amount of coolant?

[SpudRider]

Originally Posted by katflap

To me it seems counterintuitive to fill up your over flow bottle.
I'm not convinced that it can "top up" the coolant system.

If the bike were to over heat and blow, I want super hot coolant in the bottle not on me
so I leave mine empty so there's plenty of room

But that's just me

Kat,

Does the cap on your coolant overflow bottle snug securely, or does it open when you 'overtighten' it?

[Huck369]

Originally Posted by SpudRider

Kat,

Does the cap on your coolant overflow bottle snug securely, or does it open when you 'overtighten' it?

Just went out and checked mine, and it seems to seal good, and tight (I didn't "Try" to over tighten it, but what I felt was good amount of torque for a plastic bottle) so maybe yours is bad Spud...

[NoVa Rider]

Spud, the cap on my bottle tightens normally, it doesn't skip threads. I actually loosen the left side radiator so I can unhook the bottle and unscrew it, leaving the cap in place. I had no problems last week when I did this to bring the coolant up to the "full" mark on the bottle. It screwed back on correctly to a normal "tight" feel.

I think it's likely yours was overtightened at the factory and stripped. I'd try a new cap and bottle from CSC.

BTW my coolant level (in the bottle) seems to have stabilized at about half-full.

[stevecast]

Only one place for fluid to go when you overfill an overflow bottle "hence the name". More than likely, as the fluid expands from heat "while running", the excess is being forced out the drain tube. The overflow bottle should never be more than 1/4 to 1/3 full. You have to allow for fluid expansion due to heat transfer. Stop filling the bottle, and you'll be fine, so will your bike.