Transmission Oil Brown - Not loosing Coolant....?

[Noj]

Hi fellow KDX riders.

First post here. I recently picked up a 1989 KDX 200, and I love it. I don't know the history on the bike, but it fires up first kick, sounds great, runs crisp, recent carb rebuild, etc.

Lately I've noticed when I change the transmission oil, it's a bit brown or coffee - ish looking, but I'm not losing any coolant levels. I'm also using Engine Ice which is a blue coolant.

Am I possibly getting water in the transmission via a bad clutch seal on the crank case? Anyone else had this issue and possibly solved it?
Any advice would be appreciated!

[bufftester]

Coolant or water in the oil will make it look milky. Do you know if the PO ran ATF in it at all? What oil are you running in it? Keep in mind that automotive oil has friction reducers in it that are not good for wet clutch bikes.

[Noj]

I don't believe the PO ran ATF. He putted around on it on some trails and kept in a Garage, the bike is fairly clean.

Currently i have GN4 10w40 in the gear box. Been changing it every two weeks or so to this brownish metallic color. Just seems weird, and has me concerned slightly. However, zero loss of Coolant. It has stayed the same level since I flushed the radiator and put Engine Ice in it.

[doakley]

That's a four stroke engine oil. I don't know if it is really suitable for your KDX. What I read online says it is for low stress and low temperature applications. Don't know if it has friction additives in it or not. I think I would use something specifically designed for 2s wet clutches and transmissions. I personally use ATF as recommended by the manufacturer of my autoclutch. I do NOT want to start the great oil debate though!

[Noj]

Oh wow, I had no idea. The guy at the motorcycle shop just said any 10w40 would be fine in the transmission. I'll get some other stuff, and flush it out on my next day off.

[KDXGarage]

Maxima MTL-R 80 weight gear oil (10w-40 equivalent) or Bel-ray Gear Saver 80 weight gear oil have both served my various bikes well over the years.

What do you mean by clutch seal?

The 1989 - 1994 models have a water pump seal that wears out eventually. It's a 31 year old bike, so if it is original, it would be something to check after a better oil choice.

Just in case you are not familiar with the engine design, the clutch and transmission share the oil, so all the wear from the clutch, gears, etc. discolors the oil pretty quickly.

[kdxdazz]

Maxima MTL-R 80 weight gear oil (10w-40 equivalent) or Bel-ray Gear Saver 80 weight gear oil have both served my various bikes well over the years.

What do you mean by clutch seal?

The 1989 - 1994 models have a water pump seal that wears out eventually. It's a 31 year old bike, so if it is original, it would be something to check after a better oil choice.

Just in case you are not familiar with the engine design, the clutch and transmission share the oil, so all the wear from the clutch, gears, etc. discolors the oil pretty quickly.

80 weight gear oil is as thick as syrup, how is it a 10w-40 equivalent? Or am I missing something in the way it's rated, I thought all oils use SAE standards

[Noj]

Maxima MTL-R 80 weight gear oil (10w-40 equivalent) or Bel-ray Gear Saver 80 weight gear oil have both served my various bikes well over the years.

What do you mean by clutch seal?

The 1989 - 1994 models have a water pump seal that wears out eventually. It's a 31 year old bike, so if it is original, it would be something to check after a better oil choice.

Just in case you are not familiar with the engine design, the clutch and transmission share the oil, so all the wear from the clutch, gears, etc. discolors the oil pretty quickly.

Where the clutch mechanism goes into the crank case, I thought perhaps there was a seal.. A little bit of oil comes out of there and it seems like a place moisture or water could get in.

I really don't think it's the water pump seal as I'm not losing any coolant at all.

[bufftester]

The clutch and the transmission are in the same oil bath. If you look at your case you will see passages between the two halves for oil flow. Being it's coming out brown I would guess that its likely just clutch disk material. With a wet clutch like these one ride and your oil will look old, just the nature of the beast.

As for 80w gear oil vs 10w40, they are the same viscosity (or nearly the same). 75w gear oil is equivalent to 10w30. The difference between straight gear oil and the more familiar multigrades is a lot of chemistry. 10w40 means that at lower temps it flows like a 10 and at 100C it flows like a 40. This multigrade concept was developed over 50 years ago primarily to eliminate the need to change auto engine oils between summer and winter. And multigrade oils incorporate a lot of detergents and other additives. Our 2T doesn't really need them (in fact lots of auto only oils are listed as energy conserving which incorporate friction modifiers and should not be used in wet clutch applications).

[kdxdazz]

I'm familiar with the multi grade concept but I thought the higher the number the thicker the oil, I have some 80w gear oil in my shed and it's thick as f.. K, not trying to be an asshole just trying to learn so my question is how can a 80w oil be the same as a 10w oil. I often check fork oil viscosity with a simple container with a hole drilled in the bottom then time it

[bufftester]

Ok, bear in mind I am not a chemist, though I did stay at a Holiday Inn Express once...
Gear oil and crankcase oil (normal engine oil) are graded on different scales. 80W gear oil is the same as 10W40 engine oil in viscosity at operating temperature. Gear oil is designed specifically for the hydraulic forces encountered in disc packs and the shear forces induced by gears mashing together (your tranny). Engine oil is an equivalent lubricant but is designed to be more responsive to a wider range of temperatures. In autos it is also an important part of the engine cooling system, and as such reaches temperatures much higher than our 2T motors experience. Since most all the combustion heat is taken care of in the cylinder (by the water jacket), the majority of the heat encountered in the transmission is due to the actual friction of the gears working against each other (and the clutch disks working against each other) While this friction generates a lot of heat, its not nearly as much as that of an auto engine. Now, if you ride in cold climates 80W gear oil is going to make the motor very hard to kick over until it is warm, which is why you would go to a lower viscosity oil like 60W. That is why they came up with multigrade oils. But again, they are not rated on the same scale. It's like saying 100C and 212F are equivalent temps, just different scales. Remember that a gear oils viscosity is based on an operating temp of 212F. The W doesn't mean weight, its an indicator of the oils cold viscosity rating at 32F. This is why a lot of people get confused. 10W40 oil is very liquid at room temp, 80W gear oil is not. But at the operating temperatures they are rated for they have the same viscosity. Clear as brown, milky oil, right? Since most of a auto engines destructive wear is at startup you need a thinner oil at low temps to ensure that all the moving bits are properly lubricated (oil journals and such). Since a 2Ts primary wear bearings are in the cylinder well and are lubricated by the oil in your fuel you don't need a thin oil in the transmission.

Now that we've got that out there, let's talk about using ATF instead of engine or gear oil. Viscosity wise ATF is about equivalent to 5W20 engine oil, or about 65W gear oil. The primary difference is the type of additives in ATF. It's not designed to handle combustion byproducts (like you get in a auto or 4T engine)but is really well designed for hydraulic and shear forces you get in an automatic transmission which is....lots of gears mashing together. Most folks will see slightly easier shifting with ATF over gear or engine oil because remember, it's viscosity rating is at an arbitrary temperature, at low engine temps its much more fluid and so the clutch is easier to engage/disengage.

All that said, any of the 3 types of oils will work fine in our KDXs, just don't mix them.

[Noj]

Appreciate the replies regarding this -- It's my first two stroke and it's older and I really love this bike, and trying to fix up all the little things that need TLC.

Just to re-iterate this question to make sure I understand it. -- If i'm NOT losing any coolant level, then I'm not leaking any into the transmission correct? I check my coolant every day and it's the same level.

[KDXGarage]

Noj, if the level stays the same, then you aren't losing coolant.

The only way it normally escapes the system is if you really overheat it, and it boils out of the reserve tank under the left side panel.


As far as oil in general, I own a motorcycle, so I buy motorcycle oil. I have seen what transmission gears cost, so I try to keep it all as well protected as I can. I let the oil companies do the R&D, then I buy the little bottle and pour it in. Is it as cheap as using Walmart oil? No. For anyone worried about saving money, stop riding a dirt bike. It's a money pit. You are not going to do both well at the same time. :-)

[JimmyB]

https://www.bobistheoilguy.com/viscosity-charts/

On the second viscosity chart at 100deg c the SAE oils 30w and the 80w overlap some in viscosity, looks like this might be what they are rating the MC gearbox tranny oils by??? 80w MC oil is like water compared to a 80w Axle/diff/tranny gear oil..

[JimmyB]

I'm familiar with the multi grade concept but I thought the higher the number the thicker the oil, I have some 80w gear oil in my shed and it's thick as f.. K, not trying to be an asshole just trying to learn so my question is how can a 80w oil be the same as a 10w oil. I often check fork oil viscosity with a simple container with a hole drilled in the bottom then time it

I think what you have is axle/differential oil, I am not sure how they rate them as you have noted it is very thick compared to the motorcycle transmission 80w, possibly they compare them once up to operating temperature, anyways not the same don't use it.

https://www.bobistheoilguy.com/viscosity-charts/

[JimmyB]

Where the clutch mechanism goes into the crank case, I thought perhaps there was a seal.. A little bit of oil comes out of there and it seems like a place moisture or water could get in.

I really don't think it's the water pump seal as I'm not losing any coolant at all.

Check the clutch shaft at the seal and see if there is a grove worn in it from the spring, common problem on the 89-94, if oil is getting out, water is getting in either thru riding or just washing the bike.. possibly try a different brand of oil, see if it comes out the same color..

[Noj]

Where the clutch mechanism goes into the crank case, I thought perhaps there was a seal.. A little bit of oil comes out of there and it seems like a place moisture or water could get in.

I really don't think it's the water pump seal as I'm not losing any coolant at all.

Check the clutch shaft at the seal and see if there is a grove worn in it from the spring, common problem on the 89-94, if oil is getting out, water is getting in either thru riding or just washing the bike.. possibly try a different brand of oil, see if it comes out the same color..

I think I may have found the culprit with this post. There is a little grove worn and the seal looks funny below the spring is. I guess I'll have to be more careful washing it, and making sure it's in the garage on rainy days until I can fix that seal.

[kdxdazz]

I'm familiar with the multi grade concept but I thought the higher the number the thicker the oil, I have some 80w gear oil in my shed and it's thick as f.. K, not trying to be an asshole just trying to learn so my question is how can a 80w oil be the same as a 10w oil. I often check fork oil viscosity with a simple container with a hole drilled in the bottom then time it

I think what you have is axle/differential oil, I am not sure how they rate them as you have noted it is very thick compared to the motorcycle transmission 80w, possibly they compare them once up to operating temperature, anyways not the same don't use it.

https://www.bobistheoilguy.com/viscosity-charts/

Cheers guys now I understand better, yes the gear oil I have is a differential oil, it smells terrible because of the high sulphur content but I use this kind of oil only for chain lube, I find it far superior than any spray can lube, so I was wondering how anybody would put this in there motorcycle gearbox, THEY DONT. My bad

[JimmyB]

Ok, bear in mind I am not a chemist, though I did stay at a Holiday Inn Express once...
Gear oil and crankcase oil (normal engine oil) are graded on different scales. 80W gear oil is the same as 10W40 engine oil in viscosity at operating temperature. Gear oil is designed specifically for the hydraulic forces encountered in disc packs and the shear forces induced by gears mashing together (your tranny). Engine oil is an equivalent lubricant but is designed to be more responsive to a wider range of temperatures. In autos it is also an important part of the engine cooling system, and as such reaches temperatures much higher than our 2T motors experience. Since most all the combustion heat is taken care of in the cylinder (by the water jacket), the majority of the heat encountered in the transmission is due to the actual friction of the gears working against each other (and the clutch disks working against each other) While this friction generates a lot of heat, its not nearly as much as that of an auto engine. Now, if you ride in cold climates 80W gear oil is going to make the motor very hard to kick over until it is warm, which is why you would go to a lower viscosity oil like 60W. That is why they came up with multigrade oils. But again, they are not rated on the same scale. It's like saying 100C and 212F are equivalent temps, just different scales. Remember that a gear oils viscosity is based on an operating temp of 212F. The W doesn't mean weight, its an indicator of the oils cold viscosity rating at 32F. This is why a lot of people get confused. 10W40 oil is very liquid at room temp, 80W gear oil is not. But at the operating temperatures they are rated for they have the same viscosity. Clear as brown, milky oil, right? Since most of a auto engines destructive wear is at startup you need a thinner oil at low temps to ensure that all the moving bits are properly lubricated (oil journals and such). Since a 2Ts primary wear bearings are in the cylinder well and are lubricated by the oil in your fuel you don't need a thin oil in the transmission.

Now that we've got that out there, let's talk about using ATF instead of engine or gear oil. Viscosity wise ATF is about equivalent to 5W20 engine oil, or about 65W gear oil. The primary difference is the type of additives in ATF. It's not designed to handle combustion byproducts (like you get in a auto or 4T engine)but is really well designed for hydraulic and shear forces you get in an automatic transmission which is....lots of gears mashing together. Most folks will see slightly easier shifting with ATF over gear or engine oil because remember, it's viscosity rating is at an arbitrary temperature, at low engine temps its much more fluid and so the clutch is easier to engage/disengage.

All that said, any of the 3 types of oils will work fine in our KDXs, just don't mix them.

bufftester this explains a lot, thank you.. should have read this first