Engine Flush Yay or Nay?

[Kwacky]

I was thinking about getting some for the next oil change but views appear to be varied on it.

Obviously the makers of the stuff sing it's priases, but I've also read they can loosen harmless hardened oil / other contaminants and release them into the oil flow causing clogging of filters or even reducing flow.

At my last oil change I left the sump open and let some new oil run out. Is that the best thing to do?

[DaytonAndy]

At my last oil change I left the sump open and let some new oil run out. Is that the best thing to do?

That's what I've always done. A mechanic mate of mine saw me doing it and couldn't believe it. He said in every garage he's ever worked in, as soon as the oil slows to a trickle the sump bolt would be back in and filled with new oil. I did later catch him using my method on his own bike though! New oil+filter should be plenty good enough.

[Deegee]

I've used them and yes there is a risk of loosening carbon etc within oil ways which can find it's way into bearings and other critical areas, however the risk becomes greater the older an engine is or if it's very high mileage - due to more chance of carbon etc forming on the walls of internal oil ways, engines that have run over recommended oil change periods also heighten the risks. Another issue is that deposits on seals and gaskets can be removed, this could possibly lead to oil leaks, the risk is small, but is however there.

I've used them on my car engine in the past, and had no qualms. My brother has used them on his CBR600 and it really cleaned the inside of the engine. Neither had issues with engine damage or leaks, and both produced filthy oil, and surprised us afterward how clean the engine oil stayed, for signicantly longer than normal in both cases. Fwiw my car (Galaxy 2.8 ) covered nearly 300,000 miles with no engine issues, I'm sure it's isn't only down to using engine flush religiously every oil change, but I suspect it helped.

One word of warning though, use exactly as the manufacturer says, and please ensure the sump plug can be loosened before you start, I have heard of someone that drove his car to a garage complaining he added engine flush and then rounded off the sump bung. Needless to say the engine was severely damaged, the story was related to me from the mech that had to remove the bung, so I know it's not an "urban legend".

Re letting oil out, I agree with DaytonAndy, the bulk of the oil is gone so normally the plug is back in. If you want to make a better job of it, let the oil drain from hot overnight, and tilt the bike so the sump empties completely, never heard of letting fresh oil run through. Another trick if you have a decent compressor, is to wash the sump through with brake cleaner, you have to let an airline blow the fumes out or the engine is likely to head for space when it's running again, but it's a great way to get a clean sump. Don't even bother if you don't have access to compressed air through!

[Kwacky]

I didn't bother using engine flush. I did it the way I usually do and flushed some clean oil through until it ran clean. I didn't have to use much.

[duke63]

I'm not sure a properly used engine needs flushing through with a proprietary cleaner. The oil and filter should remove the majority of any nasties.