Why not change oil when engine is cold?

[bonne]

Well... it is obvious that warm oil will "run" better than cold oil... but if engine is cold and have been resting for a day, I guess most of the oil is already in the sump and not splashed all over the engine.

I mean.. I always change with warm engine... because this is what we are told. But I want to try and challenge the traditional knowledge with this question?

[Ianmc]

   The idea of warming up the oil before draining is two fold.Firstly it drains much quicker, but more importantly all of the contaminants that you are replacing the oil to get rid of, are well mixed up with the old oil,and not left lurking in the bottom of the sump or oil tank.

[porter]

 Done it both warm and cold. I know warm is supposed to better but never had a problem cold. If cold I just let the car or bike sit overnight with the sump plug out so it's well drained and it was taken a run before it cooled.

[bonne]

I just want to get as much of the old, dirty oil out before I pour in the new, fresh one. I often find that the new oil gets too dark too quickly.

To get the last drops out, I tilt the bike from side to side, set it in 6th, push the bike, and a few drops comes out again.

I am told that back in the days, people sometimes flushed the engine with some cleaning fluid for the purpose before adding the new old, but because oil today is better it is no longer needed. But maybe a good idea anyway?

[kwackboy]

Nothing wrong with flushing your engine.

In the past I've used a cheap 10w40 to flush out the old oil, then after, fill it with the good stuff.

[bonne]

Yeah, I am told that they used some kind of special fluid... you do not see it much nowadays

[Brockett]

Most ( if not all) modern engines have oil traps / wells in various places such as bearings,  that hold oil to provide essential lubrication for start ups when the engine has not been run for a while. The handbook should show there will be oil quantities for a)oil change, b) oil and filter change, and c) for engine rebuild. There may well be .75 of a litre difference between a & c .  I agree the use of oil to flush the engine but not any kind of cleaning fluid or overly thin oil as this also will be retained by the engine after it has been drained.
However, I don't. I just change the oil as the manufacturer advises. I imagine the manufacturer tests the engine and lubrication to a much higher stress level than my riding ever will and if a periodic "engine flush" is likely to extend the life or reliability of the engine "the book" would instruct me to do it.

[Fat Rat]

Don't talk about it like it was in the 1800s  I used to always flush engines between oil changes. As I keep telling my kids, the 1980s are not the olden days 

[Brockett]

Back in the day of wire mesh filters, as the oil circulated it dumped debris into small cavities in the crankcases that acted as small catch tanks. Flushing oil was used to "flush out the muck". Paper filters catch all of  that muck and so flushing is no longer required.

https://www.bennetts.co.uk/bikesocial/news-and-views/advice/bike-maintenance/best-oil-for-my-motorcycle#4

[kwackboy]

Modern oil filters don't catch everything.

Fit a sump bolt with a magnet on it and see what debris it collects.

[Brockett]

Very true. Hmmm! I must look for some magnetic plugs.

[Gert]

Using a tip for another forum, I make use of a repurposed hard drive magnet. This small magnet is stuck near the crown / dome of the oil filter. The magnet is transferred to the new filter, once the old filter is removed, thereby ensuring that any metal filings etc caught up by the magnet, remains in the removed oil filter. Easy to spot, if the magnet has not been transferred.
By and by, something else that I do, besides making a note in the service book, is to scratch the mileage of the oil change on the filter. Makes things so much easier than having to first look up the info, when doing a pre-ride inspection.