Is using flushing oil a good idea?
Q When changing the oil in my Yanmar engine (3JH4E model) I use a Pela oil extractor, which creates a vacuum to extract the old oil via the dipstick tube. However, I only get slightly over 4 litres of oil out plus what’s in the oil filter, whereas the recommended fill is 4.5 litres. As a result, after extracting as much oil as possible and changing the oil filter, the remnant old oil turns the new oil a mid to dark grey colour.
While that’s a big improvement on the old black oil, I would like to know whether use of a flushing oil would help and would be recommended. I change the oil at approximately 100-hour intervals during the season, and at the end of each season.
All the advice I have found online relates to car engines, which seem to assume that the old oil would be fully drained (via the sump plug) – a physical impossibility on my Southerly 38. I am also aware that flushing oil is generally a mineral oil, so I would be mixing mineral and synthetic oils, which probably isn’t a great idea.
Your advice on the use of flushing oil, or any other means of removing as much as possible of the old oil, would be greatly appreciated. I guess this is a common issue for yacht owners, and couldn’t find anything about flushing oil on the YM website, so I hope any response would be of interest to many of your readers. Keith Gabriel A Don Seddon, author of Diesel Troubleshooter (Fernhurst, £12.99) replies: In my experience, I would not recommend that Keith uses a flushing oil in his engine. Instead,
I would warm up the engine to the normal operating temperature then stop it. Take the starter key out, let the oil in the engine drain down into the sump for a few minutes, then insert the extractor pump pipe into the dipstick tube until you feel it touching the bottom of the sump.
After Keith has removed most of the used oil by sucking it out through the dipstick tube, I would recommend he sacrifices some new oil (say between 0.5 and 1 litre), putting it in via the filler cap. It will take a few minutes to find its way into the sump then suck the mixture of old and new out and discard.
He should then remove the extraction tube, insert the dipstick, fill with new oil and run the engine for a few minutes, before stopping it and, after a further few minutes, checking the oil level and topping up if required.
Any oil used must conform with the engine manufacturer’s specification. Do not use flushing oil as this does not contain the additives required. Dispose of used oil in a waste oil tank.