(12-21-2015, 06:39 AM)Tim_in_AZ_imp Wrote: [ -> ]Not so much the flow rate of the warmer oil, but any 'gunk' that has settled has a chance to be put back into suspension so it is flushed out.
I'm thinking most if not all of gunk should be captured by the filter, unless its pieces of really small gunk that passes through the filter. In which case I'd imagine the pieces would be brought to the sump by the returning oil anyway,to be drained out with the oil. Just MHO.
For me, the bottom line either approach is less important that following the recommended maintenance intervals.
I love these kinds of threads
For me this thread is a learning experience. Being an old dog and all, I tend to think I'm pretty sure how thngs work, how things should be done, etc because I have a lot of years of experience, even worked in the industry for nearly 2 decades, yet turns out maybe I can learn something after all.
A learning experience indeed. Changing the oil cold makes sense to me. Modern multi-grade oils seem to show little if any difference in flow whether hot or cold.
I would lean towards the oil being circulated, drained hot/warm, then allow the system time to drain fully. I also concur with the premise the oil filter [should] collect a great deal of the dirt/debris.
The filter contains much of the "solids", the dirty, contaminated fluid is removed and replaced with clean, along with a new filter.
But a brain surgeon I'm not...
The theory of changing while warm supposes that any sediments will be put into suspension and easily evacuated when drained. Conversely, draining when cold theorizes all scrud has had time to work it's way down into the crankcase and assumes it too will drain when the plug is pulled. In my experience, there will be no dirt, no debris, no particulate, no scrud to be found in any well maintained modern motorcycle engine. Why? Because of the oil filter.
Pull an oil pan or two and check for yourself. Or, if you're not up to going to that much effort, next oil change, cut open your oil filter and post up some pics of your findings. That said, if one is still concerned about sediment being left in the pan, after draining, run about a half quart of clean oil through and let it drain thoroughly before buttoning the pan back up. The theory being, a little extra rinse to clean out the pan can't hurt
Given a choice, I'll do it cold....but I won't think twice about doing it hot or warm either. Remember, it's not worth over-thinking this!
(12-21-2015, 06:39 AM)Tim_in_AZ_imp Wrote: [ -> ]Not so much the flow rate of the warmer oil, but any 'gunk' that has settled has a chance to be put back into suspension so it is flushed out.
This is the reasoning I've always been told as well. I've always somewhat blindly followed it and never questioned it.
Undeniable fact of life #39, hot oil drains faster than cold oil. So maybe the question should be, "how much is your time worth?"
I usually drain it when hot. I follow the theory that the dispersant additives in the oil (used to suspend tiny impurities in the oil and prevent sludge buildup) are doing their job when the oil is near operating temperature. The oil is also noticeably thinner when hot and definitely drains faster, and it may be my imagination, but I feel that the thinner oil drains more completely.
When it comes down to it, I'm not fanatical about doing it one way or another, but when it's convenient I do it hot.
Hot or cold, I usually let it drain for a half hour or more.
As an aside, my air-cooled airplane engine is supposed to be run to operating temp before an oil change to allow the dispersants to do their thing.