2 stroke fuel for 4 stroke engine?

[Greenheart]

Very interesting, enlightening thread, possibly because the subject is largely new to me. My question isn't only about two-stroke.

Plenty of complaints each week on this forum, about outboards not starting, or running roughly. I wonder how many could be accounted for by users' reluctance to ditch last year's fuel before starting up?

I wondered about the jerrycans of two-stroke fuel for the RIBs, in a store at the sailing club...

...they seem to be bought early in the season and used gradually, over months.

I've no idea whether fuel "stabiliser", added as soon as the fuel is put in the tank, is a reliable way to ensure petrol stays good over long periods, or whether "octane booster" can be added retrospectively to neglected fuel, to restore its usability.

So many people's lightly-used yachts seem to have half-filled petrol tanks from last season or from who-knows-when, I'd think an additive that really can recondition stale fuel, seems like it belongs on everyone's boat.

Or is it sufficient just to add plenty of fresh fuel, to liven up the old stuff?

 

[penberth3]

Why not have one container and then add oil into the ob tank when you top it up or have a plastic jug for mixing if you want to be accurate.

I remember some older engines where the inside of the filler cap was a deep cup which was the oil measure.

 

[lw395]

Our RIB fuel is not an issue.
We get through enough to turn it over.
Fuel stabiliser can help, I don't use it myself and have no problems personally becasue I'm moderately careful about not storing fuel for too long.
My bikes, which have mostly sat still all winter, I will fill up with expensive BP whatever they call the stuff that costs more.
But I've found that even with new fuel, they don't run perfectly after being idle for months. Putting a couple of tankfuls through presumably cleans things out and they run nicely after that. I have tried injector cleaner/octane booster additives, I think that speeds the cleaning process a bit, not hugely.

Plenty of other people's toys with stale fuel have been made to work by new fuel, it's the first thing I try.
I inherited a petrol strimmer which showed zero sign of starting. New fuel and off it went.

Petrol in vented tanks will go stale quite soon (3 months?) and smell wrong.
Petrol in sealed tanks does better.
Everything varies with temperature, humidity, different tanks, so other people will have slightly different anecdotal evidence.

On the whole, I don't do additives, I just concentrate on good clean fuel.

If any engine with carb(s) won't go with clean fuel, check for a spark and then clean out the carb. That's 98% of grumpy motors sorted.

 

[thinwater]

Two stroke fuel in a four stroke engine tends to run hot due to running lean, the jets are setup for all fuel and some of that area is taken up by oil so the fuel mixture is lean.

No. The oil has more BTUs/gallon than the gasoline. Many an old car has run with significant oil in the gas, and running lean is not the problem.

But eventually the plugs are going to carbon up.

One option not mentioned, which I have done many times, is to have a 2nd non-oil tank, but to turn it over every few months by using it in something else. Gasoline will EASILY keep 6 months in a container that is tightly sealed, particularity if a quality stabilizer (Biorbor EB, Merc Store-N-Start, Techron) is used (Warning--many are snake oil. These I have tested, lab and field).

 

[Greenheart]

Fascinating stuff and useful tips.

If vented tanks cause much earlier expiry on petrol, why are tanks vented?

I guess there's danger in a highly flammable liquid stored in a can that cannot let off pressure...is it all down to heat and expansion? Why don't we routinely hear of unvented tanks exploding?

There was definitely a tiny hole in the cap of the tank of my family's brand new Suffolk Punch mower, forty years ago.

My old dad still has a petrol mower in his outside shed in France, where the temperature soars and plummets, seasonally. The petrol is stored in an unvented plastic 5-litre motor-oil can, often unused for 18 months (a friend with a ride-on mower cuts his grass)...

...and when I've visited and the grass needs cutting, after priming, I've never known the mower not to start first time.

 

[lw395]

The vent is to let air in as the fuel is used.
Some engines are more or less sensitive to fuel quality.
Some people are lucky or unlucky.

 

[vyv_cox]

The vent is to let air in as the fuel is used.
Some engines are more or less sensitive to fuel quality.
Some people are lucky or unlucky.

Many an outboard motor has stopped because the driver forgot to open the vent on the cap.

 

[Greenheart]

The vent is to let air in as the fuel is used.

Thanks, that'll be the difference with the mower and its tiny tank - so the fuel for use in it, can sit in an unvented can for years.

I know a boat with a five gallon (22 litres) tank which is vented...I rather envied its ease of use and range, but I guess as soon as the full tank begins to be emptied, the fuel begins to degrade, and being only lightly used, it sits many a season before needing refilling.

I guess the solution would be to store petrol in full, tightly sealed small cans until it is needed in the outboard's built-in tank.

Sorry I've changed the direction of this thread, I may be the last person who needed telling that the contents of a vented tank need using up, although I reckon a few others might benefit by being reminded.

 

[sparkie]

Fascinating stuff and useful tips.

If vented tanks cause much earlier expiry on petrol, why are tanks vented?

I guess there's danger in a highly flammable liquid stored in a can that cannot let off pressure...is it all down to heat and expansion? Why don't we routinely hear of unvented tanks exploding?

There was definitely a tiny hole in the cap of the tank of my family's brand new Suffolk Punch mower, forty years ago.

My old dad still has a petrol mower in his outside shed in France, where the temperature soars and plummets, seasonally. The petrol is stored in an unvented plastic 5-litre motor-oil can, often unused for 18 months (a friend with a ride-on mower cuts his grass)...

...and when I've visited and the grass needs cutting, after priming, I've never known the mower not to start first time.

I've often asked the same question myself. My outboard motors over the years have been serviced, cleaned, cossetted, re-fuelled, given enough additives to start a shop, and they have- universally- always let me down, particularly in the starting department.

My old mowers were left completely alone, untouched, unloved, all winter and never failed to start first pull in the Spring. Mystifying.

 

[C08]

When I bought a 20hp 4 stroke to replace a 30hp 2 stroke I had 20 gallons of 2 stroke@50:1 to use up. I just used it (as I had no space in the tanks for neat fuel). The engine ran at the correct temperature, never fouled any plugs and had no misfire. After about 40 hours running it was all used and with no after effects.

 

[NormanS]

Thanks to all for the enlightening, and sometimes conflicting responses. Apologies for the delay, but I've been on the boat, where internet is unreliable.
My reason for the query is that in a whole six month season, I probably use less than four litres of petrol. (I normally row the dinghy). Normal petrol containers are 5 litre or more, and I don't want to have two of them, as I am never going to need anything like the quantity. Equally, I don't want to have containers with a lot of air in them.
It sounds as if the best solution for me, will be to have a single container with pure petrol, and make up "petroil" as required. Thanks to all.