Fuel System Treatment
This preparation needs to be done prior
to removing water from the engine, if that
will be part of the process.
Boatsthataregoingtobestoredforex-
tended periods (more than two [2] weeks)
or winterized should have attention for the
fuelsystem.EvenTOPTIERgasolineswill
experience some separation of elements
and settling during these periods. Of con-
siderable concern is that water condensa-
tionwilloccurwithinthefuelsystem,and
water is an enemy of good-starting and
running engine fuel systems. Therefore,
follow this procedure:
• Thefueltankshouldbeninety-to-nine-
ty-ve percent (90-95%) full of TOP
TIERgasoline.Thisallowsforminimal
room in which air can oxygenate the
fuelduringdiurnalcycles(dailyperiods
of expansion/contraction of gasoline
vapors and air as a result of temperature
changes).However,MasterCraftboats
haveEPA-dictatedfuelsystems,which
means they cannot be overlled. The
boats are equipped with ullage (over-
ow) tanks. Equipped with several
valestopreventoverow,eveninhigh
heat conditions with 100 percent full
fuel, our expansion tanks will expand
byseven-to-ninepercent(7-9%),asop-
posedtothevepercent(5%)required
bytheEPA.Astemperaturesriseinthe
tank, the pressure also rises, pushing
out gasoline vapor-and-air mixtures.
When the temperature falls, pressure
lowersandthesystemwillseektodraw
fresh air and water vapor (depending on
thehumiditylevel)intothetank.Fresh
air is replaced with “light ends,” which
are low-boiling components that vapor-
izeatambienttemperatures.Lightends
are required during cold starts to va-
porizethefuel.Sincethedailydiurnal
cycles eliminate the light ends, a full
tank helps to minimize the air volume
enteringthesystem.
• Addabiocideadditiveinthefueltank
to limit microbial growth in gasoline.
Followthedirectionsprovidedby the
additive’s manufacturer.
• Addafuelstabilizer,suchasSta-Bil
®
,
preferablytheMarinegradeorEthanol
grade stabilizer, to the fuel tank. Fol-
lowthedirectionsprovidedbythesta-
bilizer’s manufacturer.
• Runtheengineforatleastfteen(15)
minuteswhileinabodyofwater.This
allows for the circulation of the addi-
tivesthroughoutthefuelsystem.
• Duringstorage, the tankvents can be
sealed. If the vent is sealed, the tank
must NOT be completely lled. A
ninety-to-ninety-vepercent(90-95%)
lledtankallowsroomforexpansion,
which will be required at certain times
when temperatures increase. In ad-
dition to preventing water intrusion,
sealing can preventing “gumming.”
The hydrocarbons in gasoline react
with naturally occurring oxygen and
createa by-product known as “gum.”
The substance, as the name infers,
plugsupfuelltersandinjectors.Seal-
ingthetankhelpsreducegummingby
signicantlylimitingtheamountofox-
ygenavailableforinteractionwiththe
hydrocarbons.Ifthetankventissealed
for storage/winterization, it is impera-
tive to ensure that the vent is unsealed
prior to the boat being placed back into
service! Failure to do so will result in
issues in trying to ll the gas tank in
futurell-ups.
Page 6-28 2014 MasterCraft Owners Manual • Care and Maintenance
C A R E A N D M A I N T E N A N C E
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