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When we were riding yesterday, my grandson mentioned he has to add oil to the crankcase every time he rides (he's riding my old 1990 KDX 200). No leaks. I told him it was probably burning the oil through the crank seal. His spark plug looks like that could be the case. Can it be anything else?

rungrandpa wrote: 09:21 pm Jan 30 2026 When we were riding yesterday, my grandson mentioned he has to add oil to the crankcase every time he rides (he's riding my old 1990 KDX 200). No leaks. I told him it was probably burning the oil through the crank seal. His spark plug looks like that could be the case. Can it be anything else?

If it's using gearbox oil, it's very likely to have a bad right side crank seal. I highly doubt you could get open oil bath gearbox oil leaking into the coolant system, it's always the other way around where you get coolant into the oil when the water pump seal or shaft leak. There's nowhere else where it would go besides burning it or leaking it out.

You can try power washing it and degreasing it, letting it dry off, and then covering the outside of the engine with some talc powder and taking it out for a ride in dry conditions. If it's leaking externally, you will see trails in the talc powder indicating where the oil came from. Without that, you usually end up just with a big oily mess and no real idea where it originated unless you get lucky. Try that as a last resort.

Best of luck!

Good tip on the baby powder, I have a suspected air leak from my copy keihin PE, where the slide guide is pressed in, will try the baby powder trick

kdxdazz wrote: 08:56 pm Feb 01 2026 Good tip on the baby powder, I have a suspected air leak from my copy keihin PE, where the slide guide is pressed in, will try the baby powder trick

I'm not sure it'll work as well with a vacuum leak, but it works very well with oil leaks as long as the test duration is very short as to avoid excessive oil everywhere to confuse the origin/source

Chuck78 wrote: 08:42 pm Feb 02 2026

kdxdazz wrote: 08:56 pm Feb 01 2026 Good tip on the baby powder, I have a suspected air leak from my copy keihin PE, where the slide guide is pressed in, will try the baby powder trick

I'm not sure it'll work as well with a vacuum leak, but it works very well with oil leaks as long as the test duration is very short as to avoid excessive oil everywhere to confuse the origin/source

It always seems to have a ring of dust sticking to it when I go for a ride which makes me think although it's a vacuum leak,oil may also be weeping through, but I also have a small crack in the steel fuel tank which is leaking slightly so still not sure, tried my usual 3m fuel tank seal adhesive to fix it but still leaks, will try soldering next