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By Presto
If oil is working well then it ought to discolour – from carrying carbon etc. in suspension. Discolouration by itself is no sign of oil being ‘exhausted’ or in need of changing.

I'd be more concerned about quantities of sludge. That would worry me, not in connection with ‘failing’ oil but as a clue to excessive engine wear. I’d certainly want to know what’s producing heavy amounts of sludge.
By sofiaspin
Sorry I should have explained - the GT 535 is a 2016 bike and I bought it with 800 miles on the clock. The seller said it had a full service history - I take from that description that it had a 500 mile oil change and then annually. Not so. It only had the 500 mile change - so it came into my hands after three years of very occasional use, one oil change, and hence the thick oil that came out - so my view for what it is worth is more regular oil changes are better than fewer, and leaving oil in a bike that only gets started and run now and again is a bad plan. The GT goes extremely well.
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By Presto
Sure, that’s a whole different kettle of fish.

‘Using’ a bike, as you describe yours was previously ‘used’, is abuse. Short runs, low speed, standing for yonks – result sludge and worse.

The key here isn’t very frequent oil change but more frequent use of the machine!
By Andy C
Thanks for all the replies / views on the subject.

I have the comparative "luxury" of only using my bike during the summer months and I usually rack up no more than about 2000 miles in that time.

This being the case it makes sense to me to give the bike an oil change when I park it up at the end of the summer so that it is not sitting idle with "old" oil in it.

It burns very little oil so at the end of the riding season it is pretty much the same oil in there as the beginning.

Oil usually ends up pretty black but not sludgy.
By sofiaspin
Of course more frequent use is the preferred option as with anything mechanical. But with Enfields, the generally older age profile means there are a lot of low mileage bikes around. Each to his or her own but I have stuck to a more regular oil change regime for the first 2000 miles, then stick to an annual schedule. Works for me, and never had an engine fail.
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By Presto
And it’s because oil will deteriorate with time – although it must be said very much more slowly than oil companies would like to claim – it might be best to leave the old oil in the engine if laying-up for winter and putting fresh oil in the engine when it’s resurrected for the riding season.
By Andy C
Main reason for putting the new oil at the end of the season is that engine oil becomes slightly acidic with use - yes there additives that help prevent it becoming acidic but there efficiency degrades aparrently

My reasoning here is that it is better for the engine to stand idle with fresh oil in it rather than with slightly acidic oil.

In reality it probably makes very little difference.
I agree with Andy; it makes no sense leaving slightly acidic oil in the engine over winter. It isn't the oil that produces (or stops) the acidity; it's a by-product of the combustion process. I change the oil in my bikes annually. If I had only one bike and used it all the time as transport I would change it at the frequency recommended by the manufacturer. My C5 passed its second MOT yesterday - I've ridden it just over 1100 miles in a year, but I'll still change the oil when it's next due for it's annual service. BTW the oil blackens pretty quickly on the C5 too; that doesn't concern me as in my experience this has happened on every air-cooled bike I've owned, less so on liquid-cooled bikes that run at a much more stable temperature.

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