Engine flush? high milage

[kramdra]

Cbr6 is upto 108k and due an oil change. She was ran for an extended time with the oil level at or slightly below the minimum, which may have cooked it a bit so oil change is slightly early this year. There us some visible oil staining inside the engine. She doesnt burn, but fresh oil goes back very quick.

I know engine flush is generally bad, as opposed to more frequent changes and making sure the level is good.. thought it was worth asking, should I use it?

[stinkwheel]

It's not like older engines which relied on sludging to remove muck from an engine. It would build up in the sump and your engine flush would help remove it.

You have a paper element oil filter. Any nasty particulates are carried in suspension and removed by the filter in a continuous process.

If I was going to "flush" a modern engine, I'd do it with high detergent engine oil (maybe one designed for diesels) and a short-interval filter change.

However, are you fixing a problem that doesn't exist? The black is carbon deposits but the particle size will be smaller than the filter.

Personally, the most I would do is a short interval oil change unless there was convincing evidence there was a problem causing a high level of sooting (like knackered valve stem oil seals). Then I'd fix the problem.... Or actually, on a 100K plus bike I'd probably ignore it until it became impossible to ignore then swap the engine/bike.
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[RhynoCZ]

A flush should not harm the engine and it's fairly cheap. Depending on your method.

At 108k miles, I'd do the compression test and check the air/fuel mixture. The ZX7R, that I owned, had worn piston rings (oil consumption was negligible) and for some reason it ran rich in low revs (someone messed up the ram air intake system and I could never fix it). Everytime I changed the oil, it got black in a matter of hours.

Anyway, the engine ran smooth, there was a plenty of power and I did not bother doing anything to it, other than basic maintenance.

A friend of mine has a '98 Fireblade with 75k miles on it and the oil he drains from it, 8k miles intervals, is always as clean as new.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[F18]

Nah.
My 2p worth says by the time you've faffed about running flushing oil through (of dubious 'oil' properties) you are better to do short a few oil and filter changes (I never run it 8k anyway).
You could always use a lesser oil and dump it after 1,000 miles if it breaks your heart to ditch some nice 200% synth stuff.
Stain is stain but if that's all even that will clear slowly.
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[stevo as b4]

As Stinkwheel said, I'd use high detergent diesel oil for 500-1000miles and then your lube of choice with a new filter at every oil change. I used to change the oil on my ZX6R every 2000m instead of 4000m and it used to come out red like the synthetic that went in.

I've known engines that dirty/discolour the sight glass (crap compared to a dip stick anyway) and only when you remove the clutch case for other reasons can you clean the glass up enough for it to be clearly visible again. Save that job for a clutch change IMO.

[ThatDippyTwat]

Just change your oil and filter. Do it again at a shorter interval next time if you really want to set your mind at rest you got any nasties out.
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'98 VFR800 (touring) - '12 VFR800 Crosrunner (Commuting) - '01 KDX220 (Big Green Antisocial Machine)

[Robby]

I have never come across sludge in a bike engine. I've come across it in car engines that have gone a seriously long time (30k+) without an oil change.

So I doubt your problem is sludge, but it is unusual for the oil to go black very quickly. It may be that you've done enough miles to finally wear out a set of piston rings in a Japanese 4-stroke engine.

I want to say "gummed up oil control rings", but I doubt it. This bike has been used regularly, it's on modern oil, and its getting up to temperature.

Try a higher detergent oil for 1000 miles, then do an oil and filter change and go back to whatever you normally use. Might make a difference, but really it's a high miles bike where you're looking a problem that isn't really there. Ride it until it isn't worth repairing.

[ZRX61]

You can save yourself some work by taking the jug of flushing oil & pouring it straight down a drain.
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[stinkwheel]

[Bhud]

If new oil turns black quickly then it's doing its job of picking up carbon deposits and other crap from the engine? Don't see how it signifies degraded oil in any way - just means it's picked up bits so it should be OK as long it's not those silvery bits...