Infamous Coolant Overflow

[Willasan]

To start off, I've got about 1300 miles and counting on my RC390. I live near San Diego, and regularly like to go hit up Palomar mountain and the surrounding areas that are in the 3000-6000 foot in elevation range. When I first got my bike, I took it to the top of Palomar (6000ft) and it puked A LOT of coolant when I turned it off. It was also around 85-90 degrees and an uphill climb. The next time I rode down in lower elevations I pushed it a bit and it also puked a little bit out of the overflow when I turned the engine off. This wasn't nearly as severe, and I'd overfilled the overflow slightly, so I wasn't too worried. After this during my break in service, the oil was changed out with Motorex full synethic and fresh Motorex coolant was put in the bike. I haven't had any more overflow issues until this Sunday. Again while on Palomar mountain I got a bit of coolant puke out of the overflow tank when I would stop the motor. It's not a lot, just enough that I have to watch I don't ride over it on the way out. It was hot again, 80+. I was pushing the motor fairly hard, but even if I let it slow down before shutting it off it still puked. This would only happen when my motor is off and been sitting a little bit. I've never had it do this down in lower elevations (granted I haven't gone at it nearly as hard) My question is this: Is this coming from the load (heat) placed on the motor combined with the elevation? Should I be worried about this? Once I turn the motor off it gets enough heat through the coolant to go through the radiator cap into the overflow I'm guessing. Maybe I need a new radiator cap...

 

[OldVet]

The cap could be the problem I guess. Does the temp gauge show it is running hot?

 

[Willasan]

This only happens when the bike is off. It does show hot, but only if I turn the key back on. When the fan is running it never gets above two bars from the "hot" section.

 

[MrGrody]

This only happens when the bike is off. It does show hot, but only if I turn the key back on. When the fan is running it never gets above two bars from the "hot" section.

Weird. Mine will stay 2 bars away from hot section as well and it's never puked. And I'm railing it at the top of Idyllwild usually. When bike is sitting cold is ur coolant level at the lower mark? I would think maybe too much coolant possibly. I guess this cuz the three bikes I've seen puke all the dudes had way too much coolant to drink that day lol

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[ArkansasDave]

This weekend at the track my bike did the same thing. Turned the bike off and a little later the coolant slowly leaked out. My theory is after the bike is shut off the heat isn't being disapated anymore by the fan or flowing coolant so it just builds up and is able to push the cap open and overflow some. Just a theory but I haven't been able to look at the bike more, temp gauge never showed over normal operating temp and I'm using water/water wetter.

 

[Willasan]

My coolant level is right between low and high marks when cold. I'm in agreement with your assessment of why this is happening Dave. I'm wondering if my cap is faulty though, and letting the coolant out earlier than it should be.

 

[ArkansasDave]

My coolant level is right between low and high marks when cold. I'm in agreement with your assessment of why this is happening Dave. I'm wondering if my cap is faulty though, and letting the coolant out earlier than it should be.

I talked with gbaby and we both think a 1.6 bar cap might help with this. Only one way to find out.

 

[reenmachine]

I have this exact same experience riding under the same conditions -- SoCal, flogging it up the Angeles Crest to 6000' or so. I'm running distilled water and MoCool (not overfilled), and it never gets above two bars below the hot zone on the gauge. When I stop, even after letting it run down a little before shutting it off, there is audible and visible bubbling in the coolant reservoir and it pukes out the overflow. It's never done this at any other location, but this is also where it's been ridden hardest by far. It does it 100% of the time up there though.

I'm first going to install a catch can in the lower fairing to avoid the puking. I'd definitely be willing to try a higher-pressure cap too. Source?

 

[Willasan]

I have this exact same experience riding under the same conditions -- SoCal, flogging it up the Angeles Crest to 6000' or so. I'm running distilled water and MoCool (not overfilled), and it never gets above two bars below the hot zone on the gauge. When I stop, even after letting it run down a little before shutting it off, there is audible and visible bubbling in the coolant reservoir and it pukes out the overflow. It's never done this at any other location, but this is also where it's been ridden hardest by far. It does it 100% of the time up there though.

I'm first going to install a catch can in the lower fairing to avoid the puking. I'd definitely be willing to try a higher-pressure cap too. Source?

Maybe we both have faulty caps? I'm going to talk to my dealer who also owns/runs a 390 up at Palomar and see if he has any ideas. If not I'll find a different cap as well. Will update when I get more information.

 

[KTMGene390]

I'm reading these post and noticed a correlation: everyone has flushed & replaced their coolant. I could be wrong and maybe it's stating the obvious but there is an air bleed screw on the top left side of the radiator that you are supposed to open to allow air bubbles to escape when filling the radiator. Anyone with a stock bike that has not replaced their coolant having the same problem?

 

[MrGrody]

I'm reading these post and noticed a correlation: everyone has flushed & replaced their coolant. I could be wrong and maybe it's stating the obvious but there is an air bleed screw on the top left side of the radiator that you are supposed to open to allow air bubbles to escape when filling the radiator. Anyone with a stock bike that has not replaced their coolant having the same problem?

Not bleeding "blipping throttle" while filling would leave too much air in the system which would cause pressure and overflow. I'm on this one as a possibility. I'm on the stock coolant.

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[Asher]

the difference in air pressure between sea level and 6000 feet is about 0.2 bar. What's the current radiator cap rated to? 1.3bar? Since these bikes run hot already the cap might not be able to cope.
a 1.6bar cap should help.

 

[ArkansasDave]

1.4 bar is the stock cap.

 

[Willasan]

The first two times mine puked were on the stock coolant before the first service. Before any sort of flush.

 

[reenmachine]

I'm reading these post and noticed a correlation: everyone has flushed & replaced their coolant. I could be wrong and maybe it's stating the obvious but there is an air bleed screw on the top left side of the radiator that you are supposed to open to allow air bubbles to escape when filling the radiator. Anyone with a stock bike that has not replaced their coolant having the same problem?

It was doing this before I touched the system, and that's why I started looking into the change. I did follow the proper procedure and burp the system through the air bleed screw.

 

[KTMGene390]

It was doing this before I touched the system, and that's why I started looking into the change. I did follow the proper procedure and burp the system through the air bleed screw.

Yeah, I would say other than checking your radiator hoses for kinks or tie downs from the factory that are too tight over pressurizing the system, then a 1.6 bar radiator cap is probably the way to go.

 

[octaneguy]

I noticed this after my first service at about 740 miles and I parked my bike for two weeks (no time to ride), and found a puddle of coolant underneath the bike. I called up my dealership, took it back, and they said there was a faulty o-ring or something that they replaced. I don't know if that's true or not, but they said it was covered under warranty. I've since ridden over 200 miles and no more leaks, so something was fixed, lol.

 

[reenmachine]

I noticed this after my first service at about 740 miles and I parked my bike for two weeks (no time to ride), and found a puddle of coolant underneath the bike. I called up my dealership, took it back, and they said there was a faulty o-ring or something that they replaced. I don't know if that's true or not, but they said it was covered under warranty. I've since ridden over 200 miles and no more leaks, so something was fixed, lol.

I don't have any kind of leak, it just pukes through the overflow hose out the bottom.

 

[reenmachine]

Anyone know if this will fit?

HIGH PRESSURE RADIATOR CAP | Product | Moose Racing

 

[ArkansasDave]

Anyone know if this will fit?

HIGH PRESSURE RADIATOR CAP | Product | Moose Racing

i guess I could test the cap off my crf450 on the Ktm to check it out.