The answer depends on what Chain Oiler you are using, where you live and seasonal variations, please read on.....
In brief..........If you have the TUTORO Auto you can use the standard TUTORO Chain oil all year round where the ambient temps are around 25°C in the summer.
BUT if the temperature starts hitting 29° or more then you should think about using TUTORO Plus 25 Chain oil or a gear oil such as a Hypoid EP80/90 for the duration of such a hot spell.
If however you have a TUTORO Manual then you can use a Gear Oil EP80/90 all year round or the Standard TUTORO chain oil in the winter and a gear oil in the summer.
If you live somewhere where the ambient temperature is 25°C or above then you can use TUTORO Plus 25 Chain oil or a Hypoid EP80/90 Gearbox Oil in either the TUTORO Auto or the TUTORO Manual chain oilers
WARNING- NEVER USE AUTOMATIC TRANSMISSION FLUID otherwise known as ATF (more about this below)
Beware of using a Motor Oil which has a low "W" rating such as 5W-30........ 5W (where W means Winter) is designed to have a viscosity rating of only 5 (very very thin) when in a cold (read ambient) condition and a thicker 30 rating when at 100C, however in our application the oil will never reach 100C so the oil will never be thick enough to be useful.
As a guide we suggest that if you use a multigrade motor oil, whether its that old can you've had knocking around in the garage for years or an impulse purchase of the latest "Special Offer" Supermarket lube, make sure its at least 20w rated. Please bear in mind an engine oil does not have the same additives as our TUTORO chain oil.
There is an excellent article on motor oil and its viscosity here: http://www.upmpg.com/tech_articles/motoroil_viscosity/
Our chain oil is made to order and has wear modifiers, anti-friction, anti-fling and steel coating additives - engine oils are designed to do a different job and I certainly wouldn't recommend using chain oil to lube your engine!.
We have had some customers try using Chain Saw Oil but cant recommend it as it is just too sticky and glue like to flow properly at ambient temps up to 28°C. Besides which some Chainsaw oils are vegetable based - be aware some of these oils attack nitrile seals such as the O or X rings in your chain!
Lastly if you do go out to buy oil for your chain and can't get or dont want a bespoke chain oil, get some Gearbox oil, something like EP70/90 is fine if the ambient temp is warm enough! BUT....its no use using thick Gearbox oil where the ambient temperature is under 25°C, its just too thick and will only flow very slowly, for that reason we really dont recommend using 80/90 gear oil in the UK- here's hoping we have a summer that makes that possible!
Gearbox oil has got the sort of additives you need for a chain drive and it doesnt turn to a "water like" viscosity in hot weather (if you can't remember what "Hot weather" is do a Google seach on May 24th 2012 for the UK or southern Spain at almost any other date)
BUT please NEVER, EVER USE AUTOMATIC TRANSMISSION FLUID in your oiler!, some variants have all sorts of nasty toxins in and can destroy plastics, some even corrode brass!
Along with the question "What Oil should I use we are often asked "How much oil will I use?"
Generally speaking, in the summer warm dry months with little rain you will need less oil than in the winter where rain will wash off the oil in short order. For a TUTORO Auto expect summer use to be a fill approx every 800 - 1000 miles. I know some users have gone 1500 miles on a fill but a lot depends on the time spent covering those miles - ie you cover a lot more miles on a motorway in a day than you do on small back roads but the time in the saddle is the same.
During the Winter months when the temperatures remain below 25° C and rain is all too frequent, the amount of oil you should use will need to increase in order to offer any sort of protection to your chain and sprockets- so expect to almost halve the distance you can go between fill ups.
What this looks like in real terms is Summer months on an Auto on my Bike for instance, the flow control valve would be open about 1 turn but during the Winter I open up the flow control valve to 2-2.5 turns open - this does two things, it uses more oil as I need to protect the chain against the rain and salt and it compensates for the lower flow rate of the oil when cold.
An example I can give is the JABA Mundus "Round-the-World" trip guys have just updated me via Facebook. At the time of writing (June 28th 2013) they have travelled from Somerset in the UK and are now in Kazakhstan. So far they have covered nearly 21,000 Kilometres with their TUTORO Auto's on all the way (apart from some "Sand Dune crossing in North Africa). Despite this impressive distance they hae only used 250ml of chain oil. See more of their adventures on Andrew Dons's Facebook page here https://www.facebook.com/andrew.don.73
However before anyone gets too excited I must say at this point that this is not enough to preserve the longevity of their chains in particular given the serious off road nature of thousands of the kilometers that they have covered, a more realistic usage would be about 750ml if used on the road. When Off roading you need to use more oil.
All that said getting 13000 miles out of a chain on a KTM640 on the road is pretty impressive! but 13000 miles in the extreme conditions that Jon and Andrew have been riding in with a 1/3rd of the oil recommended is nothing short of astonishing!