Cruising Rpm; Fuel Requirements; Fuel Ratings; Using Reformulated (Oxygenated) Gasolines (Usa Only) - Mercury Mercruiser Tow Sport 5.7 MPI Manual

Section 4 - Specifications

Cruising RPM

Material and design advancements allow modern inboard engines operate at higher engine speeds than their predecessors.
Increased RPM significantly increases the horsepower of these new engines and is a critical part of performance and efficiency.
The materials and design of the new engines allow these higher speeds without durability penalty. Over‑propping the boat to
reduce its cruising RPM to previous levels increases the engine's susceptibility to engine damage from detonation and
pre‑ignition. The recommended cruising RPM ranges are:
Cruising RPM for Peak Efficiency
Model
Tow Sports 5.7 MPI with Gen III Cool Fuel

Fuel Requirements

IMPORTANT: Use of improper gasoline can damage your engine. Engine damage resulting from the use of improper
gasoline is considered misuse of the engine and any resulting damage will not be covered under the limited warranty.

Fuel Ratings

Mercury MerCruiser engines will operate satisfactorily when using a major brand of unleaded gasoline meeting the following
specifications:
USA and Canada—having a posted pump octane rating of 87 (R+M)/2 minimum. Premium gasoline 92 (R+M)/2 octane is also
acceptable. Do not use leaded gasoline.
Outside USA and Canada—having a posted pump octane rating of 91 RON minimum. Premium gasoline (98 RON) is also
acceptable. If unleaded gasoline is not available, use a major brand of leaded gasoline.

Using Reformulated (Oxygenated) Gasolines (USA Only)

This type of gasoline is required in certain areas of the USA. The two types of oxygenates used in these fuels is alcohol
(ethanol) or ether (MTBE or ETBE). If ethanol is the oxygenate that is used in the gasoline in your area, refer to Gasolines
Containing Alcohol.
These reformulated gasolines are acceptable for use in your Mercury MerCruiser engine.

Gasolines Containing Alcohol

If the gasoline in your area contains either methanol (methyl alcohol) or ethanol (ethyl alcohol), you should be aware of certain
adverse effects that can occur. These adverse effects are more severe with methanol. Increasing the percentage of alcohol in
the fuel can also worsen these adverse effects.
Some of these adverse effects are caused because the alcohol in the gasoline can absorb moisture from the air, resulting in a
separation of the water‑alcohol mixture from the gasoline in the fuel tank.
The fuel system components on your Mercury MerCruiser engine will withstand up to 10% alcohol content in the gasoline. We
do not know what percentage your boat's fuel system will withstand. Contact your boat manufacturer for specific
recommendations on the boat's fuel system components (fuel tanks, fuel lines, and fittings). Be aware that gasolines containing
alcohol may increase:
• Corrosion of metal parts
• Deterioration of rubber or plastic parts
• Fuel permeation through the rubber fuel lines
• Difficulty starting and operating the engine
Fuel leakage is a fire or explosion hazard, which can cause serious injury or death. Periodically inspect all fuel system
components for leaks, softening, hardening, swelling, or corrosion, particularly after storage. Any sign of leakage or
deterioration requires replacement before further engine operation.
Because of the possible adverse effects of alcohol in gasoline, we recommend only alcohol‑free gasoline when possible. If the
only fuel available contains alcohol or if you do not know whether the fuel contains alcohol, inspect for leaks and abnormalities
more frequently.
IMPORTANT: When operating a Mercury MerCruiser engine on gasoline containing alcohol, do not store the gasoline in the
fuel tank for long periods. Cars normally consume alcohol‑blend fuels before they can absorb enough moisture to cause
trouble, boats often sit idle long enough for phase separation to take place. Internal corrosion may take place during storage if
alcohol has washed protective oil films from internal components.
Page 34
WARNING
!
RPM Range
3400–3800
90-8M0076545 NOVEMBER 2012
eng