Does gasoline really go stale! Good Maintenance Manual?

[Simon]

I would be interested to know if there has been any issues with gas vapour and propane bar-b-q's?

Thanks

S

[Jack O'Brien]

Randy wrote: "If you have fuel left in your tank you may want to add some fuel stabilizer to it, so that it can be used the following season. Fuel stabilizer will also help prevent condensation from forming in your fuel tank. "

Condensation is caused only by humid air entering the tank, the tank cooling and the water vapor in the air in the tank then condensing. The best way to prevent condensation in the tank is: 1) Keep it as full as possible to prevent air entry; 2) Keep the vent closed to prevent air entry; 3) Keep the tank in a place with little daily temperature change and dry air. The "Dry Gas" alcohol additives will absorb water and be burned with the gas. The STA-BIL label says: "....Plus it contains a water remover to prevent corrosion..." But, at one ounce of STA_BIL per 2.5 gallons of gas, it can't have much water absorber to do much absorption.

[MAC26X]

I guess I'll speak up on this one. I was in the small engine business for over 25 years. Sometimes you get away with leaving gas in engines and sometimes you don't. Gas does go bad. Here are some observations:

There are many factors that influence how long gas will be "good".
1. Gas stores best in larger quantities at lower temperatures in closed containers. A 6 gal can from the boat, stored in a colder climate over the winter will probably work in the boat the next spring. But if you leave gas in a small engine all summer long (snowthrower or chainsaw) don't be suprised if the carb is gunked up.
2. Fuel stabilizers will help prevent fuel from gumming up an engine. But fuel loses it's ability to create combustion under compression whether or not it's been stabilized. It's a good policy to use stabilized fuel in small engines that may set for an unknown period of time between uses. If it's been a long time, you still may have to drain the carburetor of the old gas to get it going- you are just less likely to have to clean out clogged jets.
3. The "old" gas that won't start a small engine can often be burned up in a large automotive engine, diluted with a larger amount of good gas in the fuel tank. We used to "dispose" of all the old gas in our small engine shop by dumping it in the service truck (never more than a few gallons per tank).
4. Aviation grade fuel (80 or 100 octane) runs clean in small engines and lasts many times longer than automotive gas, even in summer climates. But it does cost more, and you have to buy it at an airport.

Small engine mechanic trick to get an engine going if the gas is a little old but the carburetor is not gummed up:

I keep a small oil/solvent squirt can filled with fresh gas (use 2-cycle mix gas if you are doing this to a 2-cycle).

Spray a few squirts into the carburetor (you may have to remove the air cleaner) and try to start the engine. If the engine starts, burns this charge, and dies, you can squirt it again carefully while it's running. After repeating this process a few times, the engine will usually run fine on its own. This is safer for the engine and mechanic than using starting fluid.

[Simon]

I guess I'll speak up on this one. I was in the small engine business for over 25 years. Sometimes you get away with leaving gas in engines and sometimes you don't. Gas does go bad. Here are some observations:

Thanks

S

[RandyMoon]

When you own a $5,000 to $8,000 outboard, it makes no sense to gamble on gas storing well over the winter. I will pull my tanks this winter and clean and dry them out. The marina at the lake has a super mechanic who will come over to my dry storage slot and flush/fog/winterize the motor for $70 bucks. That is cheap insurance for having a reliable motor next year.

[Bill at BOATS 4 SAIL]

At the end of the boating season I dump any leftover gas, even if mixed with oil, into the gas tank of my Dodge van, a gallon or two per tank of gas, and use it up that way.

[Herschel]

I discovered today when I took my 26X/50 HP Mercury out for the first time in about two months, which had run perfectly previously, that it would run fine at higher RPM's, but at lower speeds, particularly those needed for docking, it would sputter and not run smoothly. I switched to my other gas tank, but had the same problem. I am thinking it is a water condensation problem. Would adding stabilizer to the exisitng tanks help? Should I just run out the gas currently in the tanks, or should I haul the boat out of the marina slip and take it to my Mercury dealer to get it all cleaned out and, then, refill the tanks and use the gas currently in the tanks for my car, a little at at a time?

[Mark Prouty]

Herschel,

I'd top the gas tanks and replace the spark plugs and fuel filter and give it a try again.

[Catigale]

Greetings Herschel, welcome to the Board!!

The engine will run for at least 15 minutes on fuel in the line and in the engine already (maybe less at WOT) so switching tanks takes a few minutes to 'take effect'

If its water in the gas some 'dry gas' (Methanol) would help - but if you lift up the cowl and look for your fuel 'glass' (a see through plastic filter) and cant see a water layer at the bottom I doubt that water is the problem

Is your Merc Fuel injected (EFI) or carbed??

[RandyMoon]

I called my Tohatsu dealer and asked him what to do with gas over the winter. He agreed with Moe's recommendation. Add Sta-Bil to the gas and everything will be fine over the winter.

[waternwaves]

If I may add,

For those that wish to go into the chemistry of various fuel degradations, the diferences in various blends, the volatility of each of the compounds, the design metering configuration/orifices of various engines/carbs/injectors, I would love to discourse at great length. And For those of you that are familiar with the formulation of gasolines and the varous ASTM specifications and tests for all of the many types of automotive fuels done in the US you know this is not a simple question. And some fuels last longer than others,

IF you want information on the deposition gum and varnish chemicals, hey, just ask,

Basicly, Gas does age, the deterioration sequence and gums formulated during that sequence is controlled the gas blend/additives, temp and quantity of oxygen/water determines final volatility.

Remember the base fuel mix changes during the year also.... winter gas is frequently formulated with ()ane mixes varied for the time of year.

In general, smaller carbureated engines are most susceptible, to fuel gumming and degradation.
Large compuer controlled injected engines are less affected. Over a 6 month unused period, draining all small engines is preferred. (especially the bowls), dont just disconnect the fuel lines or run them till empty. For engines in the 50 HP range, with carbs like the tohatsu/nissan and the old mercs........you can get away fogging, draining and with leaving a large tank of fuel with STABIL in it. FOr a Big outboard (that hot computer controlled spark, and optimized injectior placement could probably detonate urine and carrot juice if it had to on some of these new engines...lol) with a physically large orifice size and 600 psi injection system, STick with (no pun intended) STABIL, and just minimize the amount of air exchanges in the fuel tank... (rememeber heating and cooling the fuel in the tank (day/night temp excursions) everyday increases the outgassing of the fuel. Keeping the tank full, cold and with STABIL, But much more than 6 months you almost cant get an old carbureated vehicle to start with the old gas....its indexes are so low.

In the spring, absorp all the water you can out with a fuel line dryer compatible with your carb. DO not put it during the fall, install that 1/2 hour before you use the engine.


But rare is the small carbureated engine 2-25 hp that does well with last summers light gummy deteriorated lower volatility go juice on a cool spring morning.

[Herschel]

All of the info has been very helpful. I have taken a "shotgun" approach and done just about everything everyone has advised. First, I had the Merc mechanic do the 100 hour service and vacuum test the carbs. He found one carb way out of wack and the other three needing adjustment. That done, I added Stabil, a Mercury fuel additive, and a Merc Dry Gas additive. The tank is topped off, and it runs and idles great hooked up to the water hose. As soon as we can stop having hurricanes and I can get back into the water, I'll see how she handles in the real world. Thanks for the technical info. It has been a good education on the subject.

[James V]

Dear Mark, The octane lowers over time, Put high test in when you fill up the tanks to the top.

[Herschel]

Finally got back into the water. Engine ran perfectly, better than ever before, actually, and not a flutter at low RPM's. I will use the additives for all tank fulls from now on, and I will be more careful with keeping the tank vents closed between uses. Also, I will try to top off tanks whenever possible, but I don't think I will automatically keep both tanks full unless I am anticipating a longer voyage. My concern is that I will leave one tank sitting too long and build up condensation despite additives. A definte thanks to all for the good suggestions and the good discussion on this topic.