Just a quicky... 2005 Bonnie 790 sight glass is seriously manky, planning an oil change soon so what's the consensus on using flushing oil prior to an oil & filter change? Waste of time or worth splashing for it? Odo says 27k but who knows... Thanks for your suggestions... (you can rib me if you want - I can take it - I'm a motorcyclist!!)
I wouldn't waste my money, just get the engine hot and let it drain fully then fill with good quality oil.
You are washing the inside of janky oil with more oil...I personally don't see how that would help. If you are flushing the internal of shaving & burnt gunk, I can sort of see that, but this ain't a race bike, just do your normal oil change and go on your day is my suggestion.
As some have suggested, warm the engine and drain the old oil, fit new filter and refill with fresh oil, using flushing oil removes all oil from the engine internals, not good really, so save your money and spend it on a good quality semi synthetic oil. The sight glass contamination you described is due to emulsification.
I used it once years ago on a ford Escort CVH engine in an attempt to clear blocked hydraulic tappets. It didn't work but did make the engine start weeping oil from several gaskets and seals. Never used it since and never will. I bought a 2002 very low mileage XR650 in 2010 that had been stored for years with dirty oil in the sump. I used a 10w40 diesel engine oil (NOT DIESEL FUEL!) for a couple of short duration fills, then refilled with an appropriate bike oil when the diesel stuff came out clean. Engine oil suitable for older diesels generally has higher detergency to deal with the diesel particulates.
Usually a white(ish) sludge that coats the inside of the engine, in appearance much like the cutting fluid used in engineering machine shops.
