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2020 KTM 790 Duke: Coolant getting mixed with the engine oil

23rd March 2022, 10:41 by Utkarsh Chaudhary

When the motorcycle's engine was disassembled at the service centre, it was found that all 4 intake valves were leaking.

BHPian rvrmvaishnavi recently shared this with other enthusiasts.

Hi folks,

First some background. After having dreamt of owning a big bike pretty much all my life, things finally came together for me in March 2020. I picked up a brand, spanking new KTM 790 Duke.

On paper, pretty much the perfect bike for my needs. Doesn't look or feel big. Super light, blends in, has a huge ground clearance and is easy to live with even for daily rides. Huge on power, torque and all imaginable rider aids to cover my inexperienced rear end. Made me grin like a baby every single time I twisted the throttle!

The ownership experience over the past 2 years was ok, with a few niggles here and there. Over the last 2-3 months, things turned terrible.

The whole saga started about 2 months ago.

The first symptom was an overheating caution. Rode to safety and stopped, asked the dealer for help. They asked me to bring it in. Observed that the fan was not working. Got the fan replaced under warranty. (I have replaced like 3 fans on my first batch first-gen 2013 Duke 390 so far in its 9-year lifetime, so no biggie).

Everything was fine for about 1k kms and then again, got an overheating caution. This time fan was working fine. On inspection, the coolant expansion tank was empty and the radiator was short by about 400ml. Manual says up to 500ml loss is ok, but I still reported to the dealer, who, surprised, asked me to come in again. Needless to say no obvious signs of an external coolant leak, no pooling in the parking lot, no stink of burning coolant dripping onto the header, etc.

At the dealer, dropped oil, checked the filter. Oil qty was about 2.4-2.5L (manual says 2.8L capacity) and no obvious signs of coolant in oil, very minimal stress lines seen on oil filter. But this was after 4k+ kms after the last oil and filter change and was inconclusive. So, we put in new oil and filter and decided to observe for 1k km.

Then after a day's & 700 kms ride, came back and saw that again compensating tank was empty and the radiator was short by 600ml! Decided to drain the coolant and switch to the good old regular green coolant just to ensure that we aren't missing some external leak as engine ice is a little harder to spot. Filled, bumped up the system. Updated the dealer, instruction was to come in after 1k kms as mentioned before.

Again, another day, another 2-300 km ride and another 200+ml lost in a day! Took it back to the dealer.

Once again, dropped oil. qty was fine (2.6+L), no obvious sign of coolant mixing especially given the qty of coolant lost (~1Litre). Then examined the oil filter and there was a lot more twisting of lines. A clear sign of trouble.

Started opening the engine, alternator cover. Nothing obvious. Opened the clutch cover and found a LOT of mixed oil + coolant residue.

Kind of gave up on it, left the bike with the dealer and headed home.

Sometime later, they tried to change the coolant pump gasket, checked the impeller shaft seal and replaced the heat exchanger gasket. And then tried a run on the test bench with fresh oil + filter. Once again, found strained lines in the filter. So that was not it.

Brought the engine down at the dealer. Opened the valve cover, found mixed oil + coolant on the valve cover. Then found scuff marks on the exhaust camshaft, although the claim was that it wasn't bad enough to be replaced. Removed the head and found that all FOUR intake valves were leaking!

Inspecting the head gasket showed some sort of deformation, but wasn't super clear to me personally.