How do you winter over your gas tank?

[NeedaFlyBridge]

We rented a houseboat on Shasta last week, and took along our ski boat, which has a Mercruiser 5.7 EFI. It ran great the week before during the 'shakedown' run on Hagg lake, but when we got to Shasta it wouldn't run. It would start, but would idle sortof rough, and would die if I gave it any throttle. This first started in 110 degree heat, and continued every time it got hot. I was able to run it in the cooler morning or evening, but it would not run in the heat of the day. I had two suggestions made to me, one was water in the gas, the other was vapor lock caused by high alcohol content and the heat. The fuel I was using was mostly the same fuel that had been in the tank over the winter, I had filled the tank to the brim, and had added Mercury fuel stabilizer to it. I filled the tank last Sept before they started adding the MTBE to the winter gas. I never could determine if I had water in the fuel (could not get the water separating filter off without a filter wrench, but that's another story). I finally resolved it by getting it running in the cool of the day, and running the wheels off of it at full or near full throttle until I had burned through the tank (painful since gas on the lake was $3.69/gal). After burning up the winter fuel, the boat ran great the rest of the week. I'm thinking that either the fuel went bad, or had too much alcohol, which caused vapor lock. Does this ring a bell with anyone? How do you winter over your gas tank if you store it for the winter?

Thanks, Jon

[1pump]

There isn't any MTBE in the gas around here. You may have unknowingly put oxygenated (ethanol) gas in your tank even if it was before ethanol season. Some retailers sell ethanol in their gas year-round, and it will send the RVP (vapor pressure) through the roof. I hate the stuff- it doesn't interface well with petroleum products, it absorbs water like crazy, it's hard on metal parts, and on top of that it smells like cheap tequila. :eek: As far as water in the fuel, ethanol is kind of a double-edged sword- it will enable your engine to burn the water out of the gas, but it may also put water in the gas that wasn't there in the first place.
I don't have storage issues with my gas (I use my boat all year) but it sounds like you did it right by using stabilizer and keeping the tank full.

[garyk]

Isn't Lake Shasta at a moderate altitude, like over 3000'?

Altitude, (decreased air pressure) would worsen a vapor pressure problem - especially combined with 110f temps.

For winter storage, on all the gas motors, I keep the tanks relatively full and add the appropriate amount of STABIL additive. Makes a huge difference when spring comes and you go to fire-up motors that have been sitting six months, or more.

[Chrome Bumper]

In Iraq our Yukons would vapor lock (not a good thing in a convoy in a rough neighborhood) but the land cruisers ran like a clock most of the time. Water was an issue also, but the 100+ days caused most problems. I think the engine compartment was so hot that the fuel turned to a mix of vaor and liquid which the pumps and valves would not dispense correctly. The Japanese cruisers have been used in that enviroment and the bugs worked out.
The gas there was leaded crap.

1pump and garyk got it covered pretty well. Draining the carb at the end of the season(shut off supply valve, run at fast idle til it dies) will prevent the gas from gelling or evaporating and leaving behind varnish.

Do you store your boat outside? The temperature swings will cause the gas to expand and contract. Which pumps out the high vapor pressure components of the fuel. It also puts oxygen over the gas which reacts slowly over time, can't be good. Gasoline is a mix of many many compounds all mixed together until it burns right. Kind of like american cigarettes
Also water vapor would get in, and condense.

Maybe some octane booster would have helped to salvage that one tank of gas. Is your gas cap tight and the vent in a dry location?

Gas kept in an airtight container seems to keep indefinately. But the volume/pressure inside will vary greatly.

[DonOR]

We were in Death Valley one Fall and the engine coughed once and died. As I was coming to a stop I was thinking vapor lock due to the heat, even though the old Ford had never had that problem before. I started thinking about the last gas I had gotten and then I realized I was down to 1/3 of a tank and was thinking about how hot that gas must be so I switched to the full tank, which would be colder due to the volume of gas, and it took off running again before I came to a stop. The gas probably had some alcohol in it also.

Don

[Sensei-san]

1pump has the best advice. Keeping the tank full and adding stablizer should solve the problem. With MTBE being phased out or actually gone, the only oxygenate will be ethanol. Lake Shasta is not at 3,000 feet. It is about 1,040' above sea level, so carburation adjustments are not a factor.