Why heat up multi-weight oil before changing?

I run 10W-40 in the F6B. I understand that multi-weight oils, start out thin...i.e. 10 weight when cold and then as the engine gets to operating temperature the oil thickens to a 40 weight oil...right? So basically, I am running 40 W oil after the first 10 minutes of running the engine.

If that assumption is correct, why do all info. on changing oil says to run the engine for 5 minutes or more BEFORE draining the oil? If the bike has sat for a few days and the oil is at its thinnest plus any heavier particles have settled to the bottom of the pan, isn't that the best condition to drain the oil, not when oil is thick and any anything that has settled at the bottom of the pan is redistributed throughout the motor?

Is heating up the oil before draining an "old school" practice when most oils were single weight dino based?

What am I missing?

I don't think it makes much diff. If the metal of the engine is hot I think the oil will flow out faster and more completey. Quote: why do all info. on changing oil says to run the engine for 5 minutes.... end of quote. Not all places say do it hot. I also do not think any particles should be in the oil, hot or cold as that is what a filer is for. You may be correct in that it is old school as they say.

Good question oldxtreme.

Standard oils follow a mostly linear curve when you measure viscosity versus temperature. As you mentioned, they get thinner with temperature. Multi-weight oils also get thinner with temperature, but they contain polymer chains that twist as they heat up, which make them behave like a heavier oil. This "bends" the viscosity/temperature chart. It still gets thinner as the oil gets warmer, but not as quickly as standard oil.

You're spot on that the 10w-40w will behave like a SAE10w oil at low temperatures, and then more like a SAE40w oil at operating temperature, however 40w oil at ~200degF is still thinner and more fluid than 10w oil at 40degF. It's just not as thin as 10w oil would be at ~200degF.

That said, by running the engine until warm, you're still thinning it down to make it drain easier and bring particulate into suspension so it can be swept out...you're just not getting it as thin as it would be if it were single-grade oil.

Kind Regards,
Russell

I found a quick & rough example graph on the interwebs. The lines are not really straight in real life, they're bent a bit, but it is a decent visual.

Attachment 7212

I usually end up changing it after it has sat for a few days. I figure when I park it hot everything eventually settles low. After I pull the plug and drain I sometimes pour half a quart of clean oil to rinse the last few drops laying in the bottom.

Thanks, Now this makes sense.

That chart is very revealing as to why to use multi-weight. Is the 15W-40 chart example for Rotella T6?

I like the idea of pouring some clean oil in to clean out the bottom. Seems like I always have a little oil left over from various changes. The cans just sits there just waiting for something! Now I know how to put the left overs to good use.

I remember in the "old days" you could buy flush oil or sometimes just run coal oil for a few minutes to flush out the engine and sump. That was when everything was single weight dino. Sort'a makes me sound like a dino!

Thanks again

Quote:

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Originally Posted by oldxtreme

Thanks, Now this makes sense.

That chart is very revealing as to why to use multi-weight. Is the 15W-40 chart example for Rotella T6?

I like the idea of pouring some clean oil in to clean out the bottom. Seems like I always have a little oil left over from various changes. The cans just sits there just waiting for something! Now I know how to put the left overs to good use.

I remember in the "old days" you could buy flush oil or sometimes just run coal oil for a few minutes to flush out the engine and sump. That was when everything was single weight dino. Sort'a makes me sound like a dino!

Thanks again

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Wow!! "Coal Oil". Haven't heard that phrase in a very long time. My grandfather was a machinist/tool & die maker and swore by coal oil as an antiseptic and healing aid for cuts and gouges. I tried it myself several times and it seemed like it really did speed up the healing. Of course, modern doctors don't have a clue about it.

Quote:

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Originally Posted by oldxtreme

Thanks, Now this makes sense.

That chart is very revealing as to why to use multi-weight. Is the 15W-40 chart example for Rotella T6?

I like the idea of pouring some clean oil in to clean out the bottom. Seems like I always have a little oil left over from various changes. The cans just sits there just waiting for something! Now I know how to put the left overs to good use.

I remember in the "old days" you could buy flush oil or sometimes just run coal oil for a few minutes to flush out the engine and sump. That was when everything was single weight dino. Sort'a makes me sound like a dino!

Thanks again

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I'm not sure which specific oil the chart was referencing...sorry about that. I just grabbed a generic visual that illustrated the concept. :)

I once had a lab class that had us using a rotating drum viscometer to test various SAE oils at varying temperatures and back-calculate which oil weight the sample was. JUST about the time we thought we had it down, the instructor tossed in a mystery sample (a multi-weight) and screwed everyone up. :)

I'm sure I'm gonna get some pushback, but here goes...

You can add SeaFoam to your engine oil. The mechanics at my work add the recommended amount to the work trucks just before an oil change. Then drive it around the block a few times, put it on the lift and let them drain for the night. Next morning they finish the oil change with oil only.

I did this with my VTX but haven't yet with the F6B. I've been told don't waste the money because modern oil has all the cleaners you need. I will say I do let the bike drain for several hours and, intermittently, I do sit on the bike and shake it up and down on the shocks and side to side. Get's a lot more oil to run out.