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Last thing I want is another oil thread but I can't remember ever reading about this:

As the oil gets chewed up in the bike and transmission does viscosity change ? Does it go up or down ?

Put another way: If I put 10W40 in the bike and run it 10k miles does it stay 10W40 ? Become 5W25 or 15W50 ? Become 20W30 ?

I ASSUME it gets thinner but I've been wrong before.
 

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My understanding from MCN articles is that the oil loses viscosity; i.e., 40W becomes 30W. As to whether 10W40 becomes 5W30, 5W40 or 10W30, I don't know. Interesting question.
 

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I know this isn't the most technical of answers but oil wears out, loses viscosity and lubricating properties as it becomes dirty. The only way to fix this problem is to change it. If it didn't wear out you could get by with changing the filter and not the oil.
If you have an old vehicle that uses a lot of oil, like a quart per tank of gas, then you could probably get by with just changing the filter.
 

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Multi viscosity oil is made from a base oil, by adding VI (Viscosity Index) improvers. So a 10W40 oil, is simply a 10 weight oil with viscosity index improvers (polymers) added to make it act like a 40 weight oil at higher temps.

The larger the point spread (10w to 40w) the more VI improvers that have to be added, which means the less oil you have. A typical (conventional) 10w- 40 can be 30% VI improvers, which means it only contains 70% of actual lubricant.

The VI Improver additive is the FIRST thing that breaks down in an oil, so as it does, the viscosity thins, or lightens toward the base oil.

Synthetic oils do not require as much VI improver additive to achieve the same point spread, so it won't break down as fast since the percentage of VI improvers is lower to begin with.

Also, 20w-50 could be considered superior to 10w-40 simply because it starts with a higher viscosity base oil to begin with (20 weight).

Auto manufactures backed away from 10w-40 years ago and went to 10w-30 oils because the 30 point spread in the 10w-40 required too much VI additive and breaks down too fast leaving you running almost a straight 10 weight oil in the engine after a couple thousand miles.

My BEST advice, is to change your oil OFTEN to prevent it from getting too thin, especially in hotter temps. Running a synthetic will help, but you still need to change it at the same intervals.
 

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Fred - Thanks for the education - good stuff! For all the talk one hears about extended periods between changes for synthetic oil, I still change at approx the same intervals, because synth gets dirty just like dyno, so...., this is another reason to keep doing what I've been doing.
 

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Smitty said:
Fred - Thanks for the education - good stuff! For all the talk one hears about extended periods between changes for synthetic oil, I still change at approx the same intervals, because synth gets dirty just like dyno, so...., this is another reason to keep doing what I've been doing.
You are wise to do so.
 

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Just wondering - Fred, have you ever stuck a thermocouple on your oil pan to see how much the oil temperature varies between hot weather and cold? These are liquid-cooled engines, and the water temperature is controlled by a thermostat. That temperature also affects the temperature of the oil, despite the fact that the engine oil is also circulating through, and lubricating, the transmission. My oil still gets hot at below zero temperatures, and not all that much hotter when I'm riding in temps over 100°F.
High viscosity oil is great - if you're talking about a loose-fitting air-cooled engine that might leak more than it burns (no brand names mentioned :wink: ), but in a well-designed, modern, well built engine such as in the GL1800, film strength and flow are more important. For that reason many newer cars are coming with factory fills of, and recommendations for, 5W-30 motor oils.
 
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Fred H. said:
Multi viscosity oil is made from a base oil, by adding VI (Viscosity Index) improvers. So a 10W40 oil, is simply a 10 weight oil with viscosity index improvers (polymers) added to make it act like a 40 weight oil at higher temps.

The larger the point spread (10w to 40w) the more VI improvers that have to be added, which means the less oil you have. A typical (conventional) 10w- 40 can be 30% VI improvers, which means it only contains 70% of actual lubricant.

The VI Improver additive is the FIRST thing that breaks down in an oil, so as it does, the viscosity thins, or lightens toward the base oil.

Synthetic oils do not require as much VI improver additive to achieve the same point spread, so it won't break down as fast since the percentage of VI improvers is lower to begin with.

Also, 20w-50 could be considered superior to 10w-40 simply because it starts with a higher viscosity base oil to begin with (20 weight).

Auto manufactures backed away from 10w-40 years ago and went to 10w-30 oils because the 30 point spread in the 10w-40 required too much VI additive and breaks down too fast leaving you running almost a straight 10 weight oil in the engine after a couple thousand miles.

My BEST advice, is to change your oil OFTEN to prevent it from getting too thin, especially in hotter temps. Running a synthetic will help, but you still need to change it at the same intervals.
I wonder how many of you have noticed that almost all auto maufacturers now recommend 5W-30. Their reason is simple. Lighter weight oils reduce viscous friction, hence improve gas milage. I am not aware that this has caused any reduction in engine life under normal driving conditions. The bike riding most of us do is pretty normal as far as stress on our engines or transmissions. We are not riding high performance machines.

Fred is correct. Change your oil at least according to factory intervals, or even more often. I use Honda GN4 dino and I change at +/- 4000 miles, and I don't get anal about it because it isn't a big deal. At 4K miles, my oil is discolored, but surely not what I would call "dirty", and viscosity seems much as it was when new. However, I might still change it anyway. Makes me feel good.

Synthetics are better oils, but IMHO the cost/benefit ratio isn't justified for a touring motorcycle like the Goldwing. It simply isn't going make much difference, if any.

Each to his own. Ride safe.
 

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Discussion Starter #10
The VI Improver additive is the FIRST thing that breaks down in an oil, so as it does, the viscosity thins, or lightens toward the base oil.
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So 10W40 becomes 10W30 then 10W20 but it never becomes 5WX ?
 
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