No coolant in the reservoir, and the coolant level in the radiator is two to three levels down on side stand

Chaos causes

New Member
Hello fellow riders. I own a 2016 RC390(slipper clutch model). This january I faced the same issue where the coolant reservoir tank had NO coolant in it and the service centre folks replaced the water pump seal claiming it was an coolant mixing issue with the bike. 4 months later with the lockdown going around the bike wasn't used much. And on inspecting my bike, the coolant reservoir was empty again. On ringing up my service center guys they said the engine needs to be opened up to reapply the seals. But im not sure if this is a coolant mixing issue, i feel like it's more of like a random coolant leak from the bike. I get no white smole from exhaust, have never faced a high coolant temperature or overheating ever either. Il attach the pictures20200728_212947.jpg
Coolant reservoir as of now





20200728_093036.jpg
Coolant level inside the radiator(bike is on side stand)




IMG-20200728-WA0005.jpg
Oil window as of now





IMG-20200730-WA0000.jpg
Engine oil collected now( I use liquimoly 10w50 along with motul motocool)






Screenshot_20200730-090713_WhatsApp.jpg
Oil cap as of now



Kindly help me out with this riders. The service center folks are keen on opening up the engine. Please diagnose this issue for me.
 

ReidMcT

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I think their diagnosis is correct. You have coolant in your oil.

The most likely cause is the water pump seals. It is much less likely - but still possible - that the sealant between the crankcase halves has failed around the coolant passage.

It is not at all a big job to replace the seals, and it only requires the barest degree of 'opening up the engine.' The crankcase sealant, however, is a very major job.

One thing that can help a lot is to have them install better seals... and to do it very carefully so they are perfectly straight and undamaged.

It may even be that the seals they installed don't need to be replaced but just need to be set straight.

Attached photo show the better seals from a 450, installed in my latest engine rebuild.
RC390 water pump seals from 350.jpg

Here's how it will look if the crankcase sealant needs to be redone. I've circled where the coolant passage is:
RC390 crankcase half - markup.jpg
 
Last edited:

Chaos causes

New Member
Thank you soo much. But then, with this level of coolant mixing, i was looking for some rather asssuring signs from my bike.
Do note that the engine oil I used was liquimoly10W50 and the coolant was motul motocool. A 800-1000Km run liquimoly would look just like that cup of oil right?
 

ReidMcT

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Premium Member
Elite Member
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I've suffered coolant mixing, and the only sign I got was when the oil got so thin the pressure dropped and triggered the oil light.

Maybe I misread your photo. I don't know anything about Liqui Moly oil. To me, the photo looked like the 'milkshake' sign of coolant mixing; but maybe it isn't?

If you are losing coolant, and it isn't showing in the exhaust or dripping on the ground, where else could it be other than the crankcase?

Oh, and I completely forgot to mention the very common culprit: Non-flat cylinder head, which allows coolant to get into the oil. I had that, too. The uneven spots created a void that allowed coolant to pass from the water jacket to the cam chain tunnel and down into the crankcase.

Following the method outlined by Chevalliernoir, I easily flattened the head with fine sandpapers.
 

Chaos causes

New Member
I've suffered coolant mixing, and the only sign I got was when the oil got so thin the pressure dropped and triggered the oil light.

Maybe I misread your photo. I don't know anything about Liqui Moly oil. To me, the photo looked like the 'milkshake' sign of coolant mixing; but maybe it isn't?

If you are losing coolant, and it isn't showing in the exhaust or dripping on the ground, where else could it be other than the crankcase?

Oh, and I completely forgot to mention the very common culprit: Non-flat cylinder head, which allows coolant to get into the oil. I had that, too. The uneven spots created a void that allowed coolant to pass from the water jacket to the cam chain tunnel and down into the crankcase.

Following the method outlined by Chevalliernoir, I easily flattened the head with fine sandpapers.
I'll check with the service and will keep you updated on this buddy. Thank you soo much on helping me out. And one more thing my RC390 has only run 15,942Kms.
 
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