836RADIO
New Member
Hi, I'm a KTM RC390 rider locate in Taiwan with some experience sharing in debugging the coolant overflow issue. Hope it will helpful for everyone if you are meeting related leakage problems.
I use RC390 for commuting and touring every day, the bike never shows up the high-temp alarm, but often found the coolant overflow from the expansion tank when turning off the engine after fierce driving (ex. furious driving or a long and steep uphill).
I checked out the water pump, thermostat, and cylinder head gasket, parts are OK, all work fine. I also found many people shared the way to use a 1.6bar radiator cap to fix the issue from the aftermarket. But I was afraid it may get any side effect (ex. overpressure) if I change the upper limit from the original setting.
One day, I found the pressing trace on the rubber of the radiator cap was not obvious enough(fig.1), feels like it didn’t fully catch at the bottom of the radiator opening. (Also, other riders I know meet the issue had the same symptom on their cap). For confirming the bad effect of unpressed rubber, I disassembled the radiator, make it upside down, and filled it with water. The water will leak through the pipeline linked to the expansion tank. (if you blow the compressed air into the radiator lightly, you can also find the leaked air too.) Confirmed the root cause is the cap didn’t catch well at the radiator opening bottom to block the coolant from inside the radiator, the cooling system connected with the atmosphere directly. This issue is not caused by overpressure the upper limit of 1.4bar from the original factory setting. So when shut the engine off, it stops circulating coolant, the heat will keep soaking coolant from this time, water will overflow without any cap's resistance.
Fig. 1
The radiator material includes aluminum is very soft, the radiator opening can be modified by a rubber mallet knock “lightly” along the flange. This DIY can fix the issue very quickly and with 0 costs. (fig.2 & 3) in addition, make sure to keep the whole flange flat and don't let the spring in the cap be pressed to the dead point after the tuning.
Fig.2
Fig.3
I tested over and over again for checking the improvement by ran a very steep uphill which used to overflow every time before. The result was totally OK, very successful.
List conclusion as below for all reference:
I use RC390 for commuting and touring every day, the bike never shows up the high-temp alarm, but often found the coolant overflow from the expansion tank when turning off the engine after fierce driving (ex. furious driving or a long and steep uphill).
I checked out the water pump, thermostat, and cylinder head gasket, parts are OK, all work fine. I also found many people shared the way to use a 1.6bar radiator cap to fix the issue from the aftermarket. But I was afraid it may get any side effect (ex. overpressure) if I change the upper limit from the original setting.
One day, I found the pressing trace on the rubber of the radiator cap was not obvious enough(fig.1), feels like it didn’t fully catch at the bottom of the radiator opening. (Also, other riders I know meet the issue had the same symptom on their cap). For confirming the bad effect of unpressed rubber, I disassembled the radiator, make it upside down, and filled it with water. The water will leak through the pipeline linked to the expansion tank. (if you blow the compressed air into the radiator lightly, you can also find the leaked air too.) Confirmed the root cause is the cap didn’t catch well at the radiator opening bottom to block the coolant from inside the radiator, the cooling system connected with the atmosphere directly. This issue is not caused by overpressure the upper limit of 1.4bar from the original factory setting. So when shut the engine off, it stops circulating coolant, the heat will keep soaking coolant from this time, water will overflow without any cap's resistance.
Fig. 1
The radiator material includes aluminum is very soft, the radiator opening can be modified by a rubber mallet knock “lightly” along the flange. This DIY can fix the issue very quickly and with 0 costs. (fig.2 & 3) in addition, make sure to keep the whole flange flat and don't let the spring in the cap be pressed to the dead point after the tuning.
Fig.2
Fig.3
I tested over and over again for checking the improvement by ran a very steep uphill which used to overflow every time before. The result was totally OK, very successful.
List conclusion as below for all reference:
- The radiator opening was askew, lead the rubber of the radiator cap couldn’t fully catch at the bottom of the radiator opening. The cooling system connected with the atmosphere directly. You can fix it by knocking it lightly.
- When the overflow issue happens, the pressure may not reach 1.4bar yet. As for why some people use a 1.6bar aftermarket cap to solve this problem… I haven’t compared these 2 caps, so I guess its spring is longer to catch the radiator opening bottom.
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