Need Help Coolant disappearing from 2017 KTM RC 390 race bike

naveed

Member
I have a 2017 KTM RC 390 race bike. I have removed the coolant thermostat and the bike has 2019 radiator and fan. The bike runs great without any issues.

The coolant is disappearing from the coolant reservoir and I cannot identify the exact issue. I drained the coolant, checked with vacuum radiator filler for any leaks, and refilled it. There were no leaks in the coolant system there was coolant in the engine. The vacuum refiller only refilled the radiator partially and had to put a little coolant manually (not sure if this is normal).

The engine oil color seems normal. In case you have pictures of engine oil mixed with coolant, I would be grateful if you could share them. I plan to change the water pump seals anyway, as I am not sure what else it could be. Could it be that the coolant is leaking for the reservoir overflow tube?

I am also wondering if it could be due to some underlying engine issues. I am worried that if it may be blown head gasket, but based on what I read it seems like blow head gasket is supposed to increase the coolant level in the reservoir.

I would be grateful for any help!
 

cjwell

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What coolant are you using? Something track approved I suspect. How much have you lost and over over what duration of time/track events/etc?
 

naveed

Member
I am using Red Line 80205 Supercool, which is deionized water with water wetter.

I think I am losing about 0.2 liters; I have to put approx. this much to the reservoir. I am losing this much every track day. When I ride on track for a few sessions, any time I check my reservoir is empty.
 

ReidMcT

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Same is happening to me. At least some of mine is ending up in the oil, but I don't think it all is. That makes me suspect the head gasket, even though I don't have an overheating problem.

Next month I plan to remove the engine and investigate the head. I already replaced the water pump seals, but I wonder if I didn't do that job perfectly and maybe damaged one of the seals. That could explain the seemingly small amounts of coolant in the oil.

Essentially, at this point I am uncertain whether I have one or two problems. So, while I have no answers for you, I at least have a little info to share that might help us figure this out.

Oh, and this situation also seems to be at least partially responsible the oil pressure warning I get after 450-600 miles of track riding. I find the oil filter showing signs of collapse, as if the oil/coolant mixture is clogging it more than just oil would. Or maybe that is unrelated... maybe due to clutch dust from frequent downshifting on the track?
 

Superpacman13

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I have had this problem on a few motors before. Either a lightly popped head gasket or the main case sealant has failed and is weeping coolant into the crankcase.
 

ReidMcT

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I have had this problem on a few motors before. Either a lightly popped head gasket or the main case sealant has failed and is weeping coolant into the crankcase.
Main case sealant? Can you give more details on this?
 

naveed

Member
@Superpacman13 In case of a head gasket or main case sealant failure, would there be a leak in the cooling system? I was wondering whether testing the cooling system using a vacuum filler would help detect the leak.
 

naveed

Member
I just inspected my radiator again and it was missing about 0.2 liters of coolant. I filled up the radiator and turned on the engine and rev the bike, the coolant starts to bubble and overflow; is this indicative of blown head gasket?
 

ReidMcT

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I just inspected my radiator again and it was missing about 0.2 liters of coolant. I filled up the radiator and turned on the engine and rev the bike, the coolant starts to bubble and overflow; is this indicative of blown head gasket?
No.
 

ReidMcT

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The center cases have a type of liquid sealant in between them. It can fail.
Oh... so, significant tear-down to split cases and re-seal them? I haven't examined the deign in detail, but it looks as if the water pump output probably flows from right to left across the case split. If so, I can see how that would be a weak spot.

I guess I'm going to become expert at that in the next month. I can't be changing oil every 4 track days, not to mention abusing the engine with diluted oil.

Any recommendation for case sealant? I've often used Yamabond or Permatex Ultra Grey RTV.


https://www.permatex.com/gasket-maker-comparsion-chart/

Permatex Ultra Grey description: Sensor-safe, low odor, noncorrosive. Outstanding oil resistance and joint movement tolerance. Eight times more flexible than cork/composite gaskets; three times more oil resistant than conventional silicones. Temperature range -65ºF to 500ºF (-54°C to 260°C) intermittent; resists auto and shop fluids and vibration.
 
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avs

Member
I just inspected my radiator again and it was missing about 0.2 liters of coolant. I filled up the radiator and turned on the engine and rev the bike, the coolant starts to bubble and overflow; is this indicative of blown head gasket?
That sounds like a classic head gasket failure. The bubbling is from combustion gases pushing into the coolant passages.
There are usually oil passages for the top-end in the vicinity so it is also possible that coolant will get into the oil to make a brown creamy muck in the engine oil.

But just the bubbling is enough to warrant pulling the head. I just pulled the engine, more effort than pulling my DS-7's engine, but getting bodywork/tank etc out of the way is almost half the time.
 

Petorius

New Member
I recently bought a 16 model with the engine in pieces. The head gasket had been replaced and the head skimmed but the previous owner found it was the seals on the balancer shaft leaking that were the problem. He had stripped the engine but never put it together again. This is my experience.
It should be possible (in theory) to to replace both balancer shaft seals without splitting the cases, as there is no step in the outer seal face so the seals should be able to be withdrawn externally (long self taping screw?). I replaced the balancer on mine as there was evidence of pitting on the shaft in the seal contact area. The new balancer shaft i received was different to the 15/16 fitted in that the black surface treated area on the 15/16 shaft only covered the region of the outer water pump seal whereas in the new shaft the black surface treatment extended to both seal contact areas. On mine the the balancer shaft bearing had suffered corrosion no doubt due to water getting into the bearing so needed replacing anyway, so bear this in mind. i am not sure how easy it would be to check the bearing condition visually.
 

ReidMcT

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Yes, there are threads on this forum about replacing the seals. removal is just as you proposed. Also, there is a better seal available, from IIRC a 450. Part number 77335057000
 

yogafly

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Head gasket Partial failure for sure , It happens all the time when racing the 390 and upping the rpm limit , The stock Rad is not enough. Try the adventure 390 Rad.
 

john13

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So not to bandwagon this too much, but I'm in the same boat as OP except my engine is now apart and it appears the head gasket was not the issue as it still looks pretty mint. Looking in my case a bit, it doesn't look like there is much bead left from the original case sealant so that means I need to split the cases and reseal?? Any other areas to look at?
 

ReidMcT

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So not to bandwagon this too much, but I'm in the same boat as OP except my engine is now apart and it appears the head gasket was not the issue as it still looks pretty mint. Looking in my case a bit, it doesn't look like there is much bead left from the original case sealant so that means I need to split the cases and reseal?? Any other areas to look at?
FWIW, my head gasket looked fine also. Although we have been referring to it as blown head gasket, I think of it more as leaking around the gasket. It might do well for you to use Chevalliernoir's emery paper method to see whether or not the head is truly flat. Five minutes on a glass table revealed mine to have significant low spots that would easily account for the leakage.
 

john13

Member
FWIW, my head gasket looked fine also. Although we have been referring to it as blown head gasket, I think of it more as leaking around the gasket. It might do well for you to use Chevalliernoir's emery paper method to see whether or not the head is truly flat. Five minutes on a glass table revealed mine to have significant low spots that would easily account for the leakage.
Well I already got the head and the piston shaft thing decked just in case so that won't tell me anything at this point. Going to tear down the water pump and see if that tells more of the story before splitting the case. Fingers crossed that'll solve it.....but I'm worried that I'll put it all back together and then it'll just keep leaking.
 
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