How long can Pre-mix stay mixed?

Ok, hopefully some of you have owned strokers etc or just have a working knowledge of such things ...

Anyhoo, when you pre-mix 2-smoke oil - from that moment the petrol starts degrading the oil (so I was told by a wise man) therefore pre-mix petrol/oil doesn't 'keep' for long before the oil is broken down such that it is going to be ineffective ... anyone know what this recommended max mixed storage duration is (days, weeks, months?!?). This stuff is caster based 2-smoke oil if that makes any odds?!!?

[Luckypants]

Originally Posted by Blue_SV650S

Ok, hopefully some of you have owned strokers etc or just have a working knowledge of such things ...

Anyhoo, when you pre-mix 2-smoke oil - from that moment the petrol starts degrading the oil (so I was told by a wise man) therefore pre-mix petrol/oil doesn't 'keep' for long before the oil is broken down such that it is going to be ineffective ... anyone know what this recommended max mixed storage duration is (days, weeks, months?!?). This stuff is caster based 2-smoke oil if that makes any odds?!!?

My mower / strimmer / chainsaw man says 6 weeks.

Months definitely and years possibly! At least in outboard engines. I've been using 50:1 mix using pump unleaded and Quicksilver 2stroke oil for years and never had any problems. In the years before then I used 25:1 but that was for Anzani and Seagull outboards rather than the sophisticated Mariner/Yamaha/Johnson/Evinrudes since. I think that the most important aspect of two strokes using pre mix is that the mix is accurate.

Frequently I've left a gallon or two or five over a winter in a can and its been OK come the following summer. I've never heard of it degrading petrol although poor quality 2st oil used to "settle" out so I still always shake the can before putting it in the tank.

When I had two stroke bikes the mix was never around for long enough to find out if it degraded but then I used whatever I could find and frequently used any old oil if the proper stuff wasn't immediately to hand. Maybe that's why a certain GT380 tried killing me on two occasions.....

I have a mate with a NSR250 70+hp screamer and I've never heard him mention having any issues with 2st oil so I'd say that if kept for any length of time a vigorous shake prior to pouring would be a wise move but apart from that I don't think it degrades any more than petrol deteriorates on its own.

Petrol does go "off" but I think that depends on ambient temperature more than anything else but I was told that if it still smells like petrol it'll still go like petrol!

HTH
Cheers
DP

This stuff is castor based race oil ... mixed at 16:1 ... it's for a racing Kart engine ... my mate has had it sat mixed for at least a month ... I have never personally used pre-mix after day of mixing as I just sling left-over in my SV ... my mate has this stuff and asked me if I thought it'd be ok still ... I said, dunno, maybe, but is it worth risking blowing you engine up over £6 of fuel/oil?!!?

So we have 6 weeks (possibly more by the sounds of the outboards ) is ok ... but I am not sure if it being castor it is more susceptible than normal 2-smoke oil mind also this kart engine is under quite a bit of stress?!?!? this Kart engine spins up to about 21k RMP

Addenuf - ya outboards were pre-mix, but the GT380 (I had a GT185 ) and the NSR would be injector, not pre-mix

I think a MX bike is about the closest relation to a go-kart engine in stress levels ... Anyone got an MX bike and they have stored pre-mix for any length of time?!

had pre mix in the jet ski for a few months....still goes ok....and its the same oil i put in the minimoto.

well it lasted for months fine in my dads 59 scott flying squirel, infact having had the tank off for 4 months whilst working on it it started first kick and fell happily onto idle with no problems on stuff he had mixed up the last time he had gone riding which is not a common thing, hes more of a tinkerer than a rider. Id say he rides it maybe 4 or 5 times a year and only to classic rallies and im positive he doesnt empty the tank and fill it up with new premix every time he rides it. Id say it would be absolutely fine but do give it a shake before use cause it will separate out due to weight of the oil compared to the petrol.

just give it a bit of a shake b4 use, as the oil can settle at the bottom,

It is supposed to be used pretty much straight away, but I think that is because of performance rather than lubrication issues - however, if it is going in an expensive or high performance engine then err on the safe side and mix up no more than a week before.

Andy