Quote:
Originally Posted by pothole
Hmm. In my experience the rate of flow becomes absolutely teeny after about an hour. Can't really see the benefit of leaving it overnight. However you do it, there's going to be a fair bit of old oil left. Well, unless you fill it, run it and flush it a few times before refilling.
If you want to really reduce the amount of old oil residue, I think you need to completely fill it after draining, run it for a while and then dump and refill. Leaving it for hours and hours to drain doesn't make much difference to the residue stuck to all parts of the engine.
Personally, I just drain it for about an hour from warm and refill but I do my changes fairly frequently - around every 5k miles - so I really don't worry about a little residue. Fortunately, these cars take a **************** load of oil, so any residue gets pretty well diluted.
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If you read the entire thread you will see that I'm not saying drain for hours
. I'm saying if you let the car sit overnight (do not start before draining), it is equivalent to draining for hours because the oil has gathered at the sump. At this point 30min should drain every possible bit of oil out of the engine. If sludge is your concern, because the car was parked at operating temps, I would assume the sludge would also gather at the sump at this point.