Operation Manual

Fuel System Treatment
This preparation needs to be done prior
to removing water from the engine, if that
will be part of the process.
 Boatsthataregoingtobestoredforex-
tended periods (more than two [2] weeks)
or winterized should have attention for the
fuelsystem.EvenTOPTIERgasolineswill
experience some separation of elements
and settling during these periods. Of con-
siderable concern is that water condensa-
tionwilloccurwithinthefuelsystem,and
water is an enemy of good-starting and
running engine fuel systems. Therefore,
follow this procedure:
• Thefueltankshouldbeninety-to-nine-
ty-ve percent (90-95%) full of TOP
TIERgasoline.Thisallowsforminimal
room in which air can oxygenate the
fuelduringdiurnalcycles(dailyperiods
of expansion/contraction of gasoline
vapors and air as a result of temperature
changes).However,MasterCraftboats
haveEPA-dictatedfuelsystems,which
means they cannot be overlled. The
boats are equipped with ullage (over-
ow) tanks. Equipped with several
valestopreventoverow,eveninhigh
heat conditions with 100 percent full
fuel, our expansion tanks will expand
byseven-to-ninepercent(7-9%),asop-
posedtothevepercent(5%)required
bytheEPA.Astemperaturesriseinthe
tank, the pressure also rises, pushing
out gasoline vapor-and-air mixtures.
When the temperature falls, pressure
lowersandthesystemwillseektodraw
fresh air and water vapor (depending on
thehumiditylevel)intothetank.Fresh
air is replaced with “light ends,” which
are low-boiling components that vapor-
izeatambienttemperatures.Lightends
are required during cold starts to va-
porizethefuel.Sincethedailydiurnal
cycles eliminate the light ends, a full
tank helps to minimize the air volume
enteringthesystem.
• Addabiocideadditiveinthefueltank
to limit microbial growth in gasoline.
Followthedirectionsprovidedby the
additive’s manufacturer.
• Addafuelstabilizer,suchasSta-Bil
®
,
preferablytheMarinegradeorEthanol
grade stabilizer, to the fuel tank. Fol-
lowthedirectionsprovidedbythesta-
bilizer’s manufacturer.
• Runtheengineforatleastfteen(15)
minuteswhileinabodyofwater.This
allows for the circulation of the addi-
tivesthroughoutthefuelsystem.
• Duringstorage, the tankvents can be
sealed. If the vent is sealed, the tank
must NOT be completely lled. A
ninety-to-ninety-vepercent(90-95%)
lledtankallowsroomforexpansion,
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
createa by-product known as “gum.”
The substance, as the name infers,
plugsupfuelltersandinjectors.Seal-
ingthetankhelpsreducegummingby
signicantlylimitingtheamountofox-
ygenavailableforinteractionwiththe
hydrocarbons.Ifthetankventissealed
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
futurell-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