Two-stroke mix

[pugwash]

How can you tell if a can of petrol is already mixed with oil for running two-strokes?
If you run an outboard with double the oil mix (preferable, I suppose, to running it without oil at all) does it matter that much?

 

[Eudorajab]

Haed to start and pretty smokey from my experience.

 

[david_bagshaw]

Take a teaspoon of the questionable mix, & put on a kitchen towel & let evapourate an oily stain will result, compare to the same with ordinary petrol from another source..

Often mixed petrol looks a slightly different colour as well. As to running engin with double mix , , becomes difficult to start next time , as the pipe from the tank is full of normal mix, unless this is the first start of the season, when it will be extra difficult to start due to the ageing prosess that takes place to old fuel.

As to running with no oil....... expensive & not covered by warranty.

PS dont smoke while doin the test!!!!!!

Have fun

David
www.euroboating.net

 

[oldharry]

Most 2 stroke oils have a dye to avoid this confusion. Obviously running without oil will be rapidly terminally fatal to the engine. The efect of doubling the mix depends to some degree on the ratio the engine requires.

Engines running 100:1 will almost always actually benefit from running 50:1 - most engine service shops recommend this for longevity, as there is really insufficient oil at 100:1 mix to prevent accelerated wear.

50:1 increased to 25:1 will be smoky but is just about acceptable for most engines. carry a spare set of plugs as they will almost cetainly oil up! With any lower ratio it is inadvisable to run with doubled oil mix as the carburation will be upset, the engine will be runing on a lean fuel mix with - depending on the size and power of the engine - potential for damage, as well as bad starting, fouling plugs etc etc.

The best bet, if you are uncertain is to offload the queried fuel mix into your car next time you fill up. It will do no harm as long as you are not about to have it MOT'd when it might mess up the emissions test. By the time you have mixed the rest of the tankful the ratio will probably be several hundred to one - unless you have a lot of it.

 

[bedouin]

As suggested above - if this is last year's mix then I would recommend using it in the car and getting a fresh lot for the boat - won't harm the car.

It can be very difficult/impossible to start an outboard using old petrol.

 

[tonyleigh]

I'm open to correction but wouldn't an oil mix be risky with a catalytic converter?

 

[BarryD]

Destroy the converter more like it.

It might work on older cars with non injection / cat. systems - but on a new one it will kill the cat. Surely a better bet is to try to correct the mix by adding fresh (new) fuel and oil to the existing mix in the correct quantities, yes it will be diluted but the worst case would be 25litres of fuel to mix.

Barry D.

IMHO & FWIW, NWGOI.

 

[pugwash]

Brilliant lateral thinking. Thanks!

 

[david_e]

<<Engines running 100:1 will almost always actually benefit from running 50:1 - most engine service shops recommend this for longevity, as there is really insufficient oil at 100:1 mix to prevent accelerated wear.>>

Can't agree I'm afraid, this thought line is old wives stuff with a modern engine. I fell for it earlier last year, specialist Marine engineer (plonker in reality) said that is what you do. In the end one of the plugs whiskered and caused a power problem, easily solved but could have done without the hassle.

If it says 100:1 then the guys who make the engine have designed it that way, ngineering tolerances are much better than they ever were and oils have improved alot as well, these result in greater efficiency alround.

 

[oldharry]

Whiskering normally only happens if you use the wrong grade of 2t oil, and is cured by changing the brand you buy. Met it several times in different engines, and this invariably cures it.

Engine designers advising 100:1 are trying to solve the ecological and environmental problems inherent in 2 strokes which will NEVER burn all the oil they use, and will always discharge a small amount into the environement. Remember the oil slick the old 10:1 mix Seagull used to leave behind it? Quite effective at smoothing a rough following sea....

Of course the engine will run on 100:1 if it is designed for it, but the cost is in increased wear through oil starvation, and the service life is reduced accordingly. Of course the designers are not worried, because built in obsolescence is good for profit.

And to those who are concerned about the cat convertors in the car - apologies! You are of course absolutley right. 2T oil is no good for them at all. My comment reflects on how long I have been using diesel cars.

 

[quaelgeist2]

A bit off the thread, but since you mentioned it...

My engine shop recommended to go from 1:50 to 1:100 ! He said the Mercury 9.9 had been designed for full throttle operation, hence the 1:50.
On my boat, operating with a working prop in a well and normally never reaching nominal revs it is supposedly healthier to reduce the mix.

Any opinions (strong ones please, since I have practised it successfully since!)

chris

 

[andy_wilson]

Dump it!

Preferably in the tank of a non-cat fitted vehicle. The oil will damage a catalytic converter.

Double mix is a shortcut to a de-coke or worse.

Half mix is OK at light loads (auto mix engines run at about 1/3 at tick over, 1/2 strength at light loads, and full strength at full throttle).

No oil is bad news except for v. short periods (I had a Johnson 70 with auto mix that would run up to 2,000 rpm if the oil tank was empty but that was to get you out of danger).

If it is so old you can't remember, the oomph has probably gone from the fuel anyway. Stale fuel is the usual cause of hard starting.

If your car has a cat. convertor, save the old fuel for cleaning the trailer wheel bearings or your winches, starting the BBQ (joke) or something.