Lexus LX 470 1998 Owner's Manual page 275

ENGINE
FUEL
Fuel type
Your vehicle must use only unleaded gasoline.
To help prevent gas station mixups, your Lexus has a smaller fuel
tank opening. The special nozzle on pumps with unleaded fuel will
fit it, but the larger nozzle on pumps with leaded gas will not.
At a minimum, the gasoline you use should meet the specifications
of ASTM D4814 in the U.S.A. and CGSB 3.5−M93 in Canada.
NOTICE
Do not use leaded gasoline. Use of leaded gasoline will cause the
three−way catalytic converter to lose its effectiveness and the
emission control system to function improperly. Also, this can
increase maintenance costs.
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Octane rating
Select premium unleaded gasoline with an Octane Rating of 91
(Research Octane Number 96) or higher for optimum engine
performance. However, if such premium type cannot be
obtained, you may temporarily use unleaded gasoline with an
Octane Rating as low as 87 (Research Octane Number 91).
Use of unleaded fuel with an octane number or rating lower than
stated above will cause persistent heavy knocking. If severe, this
will lead to engine damage.
If your engine knocks ...
If you detect heavy knocking even when using the recommended
fuel, or if you hear steady knocking while holding a steady speed on
level roads, consult your Lexus dealer.
However, now and then, you may notice light knocking for a short
time while accelerating or driving up hills. This is no cause for
concern.
Gasolines containing detergent additives
Lexus recommends use of gasolines that contain detergent
additives to avoid build−up of engine deposits.
For further details, ask your Lexus dealer or a local gasoline retailer.