1998 TOYOTA SIENNA cooling

name. SIENNA (U)
104
With tachometer
Without tachometer
The gauge indicates the engine coolant
temperature when the ignition switch is
on. The engine operating temperature
will vary with changes in weather and
engine load.
If the needle moves into the red zone,
your engine is too hot. If your vehicle
overheats, stop your vehicle and allow the
engine to cool.
Your vehicle may overheat during severe
operating conditions, such as:
Driving up a long hill on a hot day.
Reducing speed or stopping after high
speed driving.
Idling for a long period with the air
conditioning on in stop−and−go traffic.
Towing a trailer.
NOTICE
Do not remove the thermostat in
the engine cooling system as this
may cause the engine to overheat.
The thermostat is designed to con-
trol the flow of coolant to keep the
temperature of the engine within
the specified operating range.
Do not continue driving with an
overheated engine. See ”If your ve-
hicle overheats” in Part 4.
Engine coolant temperature
gauge
ProCarManuals.com

name. SIENNA (U)
148
Heating
For best results, set controls to:
Fan speed —Any setting except ”OFF”
Temperature —Towards WA R M
(red zone)
Air intake —FRESH (outside air)
Air flow —FLOOR
Air conditioning —OFF
For quick heating, select recirculated
air for a few minutes. To keep the
windows from fogging, select fresh af-
ter the vehicle interior has been
warmed.
Press the ”A/C” button on for dehumidi-
fied heating.
Choose floor/windshield air flow to heat
the vehicle interior while defrosting or
defogging the windshield.Air conditioning
For best results, set controls to:
Fan speed —Any setting except ”OFF”
Temperature —Towards COLD
(blue zone)
Air intake —FRESH (outside air)
Air flow —PA N E L
Air conditioning —ON
For quick cooling, move the air intake
selector to recirculate for a few min-
utes.
Ventilation
For best results, set controls to:
Fan speed —Any setting except ”OFF”
Temperature —Towards COLD
(blue zone)
Air intake —FRESH (outside air)
Air flow —PA N E L
Air conditioning —OFF
Defogging
The inside of the windshield
For best results, set controls to:
Fan speed —Any setting except ”OFF”
Temperature —Towards WA R M
(red zone) to heat;
COLD (blue zone) to
cool
Air intake —FRESH (outside air)
Air flow —WINDSHIELD
Turning the air flow control knob to wind-
shield position turns on the defroster−
linked air conditioning. At this time, the
”A/C” button indicator comes on regard-
less of whether or not the ”A/C” button is
pressed in. This is to clean up the front
view more quickly.
When the ”A/C” button is not pressed in,
turning the air flow control knob to anoth-
er position turns off the air conditioning.
On humid days, do not blow cold air
on the windshield—the difference be-
tween the outside and inside tempera-
tures could make the fogging worse.
ProCarManuals.com

name. SIENNA (U)
170
NOTICE
A large amount of unburned gases
flowing into the three−way catalytic
converter may cause it to overheat
and create a fire hazard. To prevent
this and other damage, observe the
following precautions:
Use only unleaded gasoline.
Do not drive with an extremely low
fuel level; running out of fuel could
cause the engine to misfire, creat-
ing an excessive load on the three−
way catalytic converter.
Do not allow the engine to run at
idle speed for more than 20 min-
utes.
Avoid racing the engine.
Do not push−start or pull−start your
vehicle.
Do not turn off the ignition while
the vehicle is moving.
Keep your engine in good running
order. Malfunctions in the engine
electrical system, electronic ignition
system/distributor ignition system
or fuel system could cause an ex-
tremely high three−way catalytic
converter temperature.
If the engine becomes difficult to
start or stalls frequently, take your
vehicle in for a check−up as soon
as possible. Remember, your Toyota
dealer knows your vehicle and its
three−way catalytic converter sys-
tem best.
To ensure that the three−way cata-
lytic converter and the entire emis-
sion control system operate proper-
ly, your vehicle must receive the
periodic inspections required by the
Toyota Maintenance Schedule. For
scheduled maintenance information,
refer to the separate ”Owner’s
Manual Supplement/Maintenance
Schedule”.
Engine exhaust cautions
CAUTION
Avoid inhaling the engine exhaust.
It contains carbon monoxide, which
is a colorless and odorless gas. It
can cause unconsciousness or even
death.
Make sure the exhaust system has
no holes or loose connections. The
system should be checked from
time to time. If you hit something,
or notice a change in the sound of
the exhaust, have the system
checked immediately.
Do not run the engine in a garage
or enclosed area except for the
time needed to drive the vehicle in
or out. The exhaust gases cannot
escape, making this a particularly
dangerous situation.
Do not remain for a long time in a
parked vehicle with the engine run-
ning. If it is unavoidable, however,
do so only in an unconfined area
and adjust the heating or cooling
system to force outside air into the
vehicle.
ProCarManuals.com

name. SIENNA (U)
171 
Keep the back door and quarter
windows closed while driving. An
open or unsealed back door and
quarter windows may cause exhaust
gases to be drawn into the vehicle.
To allow proper operation of your
vehicle’s ventilation system, keep
the inlet grilles in front of the wind-
shield clear of snow, leaves, or oth-
er obstructions.
If you smell exhaust fumes in the
vehicle, drive with the windows
open and the back door and quarter
windows closed. Have the cause im-
mediately located and corrected.
FUNCTIONS OF ENGINE OIL
Engine oil has the primary functions of
lubricating and cooling the inside of the
engine, and plays a major role in main-
taining the engine in proper working order.
ENGINE OIL CONSUMPTION
It is normal that an engine should con-
sume some engine oil during normal
engine operation. The causes of oil
consumption in a normal engine are as
follows.
Oil is used to lubricate pistons, piston
rings and cylinders. A thin film of oil
is left on the cylinder wall when a pis-
ton moves downwards in the cylinder.
High negative pressure generated when
the vehicle is decelerating sucks some
of this oil into the combustion chamber.
This oil as well as some part of the oil
film left on the cylinder wall is burned
by the high temperature combustion
gases during the combustion process.
Oil is also used to lubricate the stems
of the intake valves. Some of this oil
is sucked into the combustion chamber
together with the intake air and is
burned along with the fuel. High tem-
perature exhaust gases also burn the
oil used to lubricate the exhaust valve
stems.The amount of engine oil consumed de-
pends on the viscosity of the oil, the
quality of the oil and the conditions the
vehicle is driven under.
More oil is consumed by high−speed driv-
ing and frequent acceleration and decel-
eration.
A new engine consumes more oil, since
its pistons, piston rings and cylinder walls
have not become conditioned.
When judging the amount of oil con-
sumption, note that the oil may become
diluted and make it difficult to judge
the true level accurately.
As an example, if a vehicle is used for
repeated short trips, and consumes a nor-
mal amount of oil, the dipstick may not
show any drop in the oil level at all, even
after 1000 km (600 miles) or more. This
is because the oil is gradually becoming
diluted with fuel or moisture, making it
appear that the oil level has not changed.
The diluting ingredients evaporate out
when the vehicle is then driven at high
speeds, as on an express way, making it
appear that oil is excessively consumed
after driving at high speeds.
Facts about engine oil
consumption
ProCarManuals.com

name. SIENNA (U)
193
If your vehicle overheats
If your engine coolant temperature
gauge indicates overheating, if you ex-
perience a loss of power, or if you hear
a loud knocking or pinging noise, the
engine has probably overheated. You
should follow this procedure...
1. Pull safely off the road, stop the ve-
hicle and turn on your emergency
flashers. Put the transmission in ”P”
and apply the parking brake. Turn off
the air conditioning if it is being used.
2. If coolant or steam is boiling out of the
radiator or reservoir,stop the engine.
Wait until the steam subsides before
opening the hood. If there is no coolant
boiling over or steam, leave the engine
running and make sure the electric
cooling fan is operating. If it is not,
turn the ignition off.
CAUTION
To help avoid personal injury, keep
the hood closed until there is no
steam. Escaping steam or coolant is
a sign of very high pressure.
3. Look for obvious coolant leaks from the
radiator, hoses, and under the vehicle.
However, note that water draining from
the air conditioning is normal if it has
been used.
CAUTION
When the engine is running, keep
hands and clothing away from the
moving fan and engine drive belts.
4. If the coolant is leaking, stop the en-
gine immediately. Call a Toyota dealer
for assistance.
5. If there are no obvious leaks, check
the coolant reservoir. If it is dry, add
coolant to the reservoir while the en-
gine is running. Fill it about half full.
CAUTION
Do not attempt to remove the radiator
cap when the engine and radiator are
hot. Serious injury could result from
scalding hot fluid and steam blown
out under pressure.
6. After the engine coolant temperature
has cooled to normal, again check the
coolant level in the reservoir. If neces-
sary, bring it up to half full again. Seri-
ous coolant loss indicates a leak in the
system. You should have it checked as
soon as possible at your Toyota dealer.
ProCarManuals.com

name. SIENNA (U)
220
1. Engine coolant reservoir
2. Power steering fluid reservoir
3. Engine oil level dipstick
4. Engine oil filler cap
5. Brake fluid reservoir
6. Fuse blocks
7. Battery
8. Electric cooling fans
9. Windshield and rear window washer fluid
tank
Engine compartment overview
ProCarManuals.com

name. SIENNA (U)
223 
Be sure that the ignition is off if
you work near the electric cooling
fans or radiator grille. With the
ignition on, the electric cooling fans
will automatically start to run if the
engine coolant temperature is high
and/or the air conditioning is on.
Use eye protection whenever you
work on or under your vehicle
where you may be exposed to flying
or falling material, fluid spray, etc.
Used engine oil contains potentially
harmful contaminants which may
cause skin disorders such as in-
flammation or skin cancer, so care
should be taken to avoid prolonged
and repeated contact with it. To re-
move used engine oil from your
skin, wash thoroughly with soap
and water.
Do not leave used oil within the
reach of children.
Dispose of used oil and filter only
in a safe and acceptable manner.
Do not dispose of used oil and fil-
ter in household trash, in sewers or
onto the ground. Call your dealer or
a service station for information
concerning recycling or disposal.
NOTICE
Remember that battery and ignition
cables carry high currents or volt-
ages. Be careful of accidentally
causing a short circuit.
Add only demineralized or distilled
water to fill the radiator. And if you
spill some of the coolant, be sure
to wash off with water to prevent it
from damaging the parts or paint.
Do not allow dirt or anything else
to fall through the spark plug holes.
Do not pry the outer electrode of a
spark plug against the center elec-
trode.
Use only spark plugs of the speci-
fied type. Using other types will
cause engine damage, loss of per-
formance or radio noise.
Do not reuse platinum−tipped spark
plugs by cleaning or regapping.
Do not overfill automatic transmis-
sion fluid, or the transmission
could be damaged.
Do not drive with the air cleaner
filter removed, or excessive engine
wear could result. Also backfiring
could cause a fire in the engine
compartment.
Be careful not to scratch the glass
surface with the wiper frame.
When closing the engine hood,
check to see that you have not for-
gotten any tools, rags, etc.
ProCarManuals.com

name. SIENNA (U)
227
Look at the see−through coolant reser-
voir when the engine is cold. The cool-
ant level is satisfactory if it is between
the ”FULL” and ”LOW” lines on the
reservoir. If the level is low, add ethyl-
ene−glycol type coolant.
The coolant level in the reservoir will vary
with engine temperature. However, if the
level is on or below the ”LOW” line, add
coolant. Bring the level up to the ”FULL”
line.
Use only ethylene−glycol type coolant.
See information in the next column.
If the coolant level drops within a short
time after replenishing, there may be a
leak in the system. Visually check the
radiator, hoses, engine coolant filler cap,
radiator cap and drain cock and water
pump.
If you can find no leak, have your Toyota
dealer test the cap pressure and check
for leaks in the cooling system.
CAUTION
To prevent burning yourself, do not
remove the radiator cap when the en-
gine is hot.
Coolant type selection
Your coolant must contain ethylene−glycol
antifreeze. In addition to preventing freez-
ing and subsequent damage to the engine,
this will also prevent corrosion. Further
supplemental inhibitors or additives are
neither needed nor recommended.
Read the antifreeze container for informa-
tion on freeze protection. Follow the
manufacturer’s directions for how much to
mix with water. The total capacity of the
cooling system is given in Part 8. We
recommend 50% solution be used for your
Toyota, or a sufficient quantity to provide
protection to about −35C (−31F).
NOTICE
Do not use alcohol type antifreeze or
plain water alone.
Checking brake fluid
To check the fluid level, simply look at
the see−through reservoir. The level
should be between the ”MAX” and
”MIN” lines on the reservoir.
It is normal for the brake fluid level to go
down slightly as the brake pads wear. So
be sure to keep the reservoir filled.
If the reservoir needs frequent refilling, it
may indicate a serious mechanical prob-
lem.
If the level is low, add SAE J1703 or
FMVSS No. 116 DOT 3 brake fluid to
the brake reservoir.
Remove and replace the reservoir cover
by hand.
Checking the engine coolant
level
ProCarManuals.com