Page 272 of 430

Engine Oil (DURAMAX®/Isuzu Diesel
Engine)
Checking Engine Oil
It is a good idea to check the engine oil level
every time you get fuel.
The engine oil dipstick
is located in the engine
compartment on the
driver’s side of the
vehicle.In order to get an accurate reading, the engine
should be at normal operating temperature, so
that the oil is warm, and the vehicle must be
on level ground.
1. If the engine is at normal operating
temperature and the oil is warm, turn off the
engine and allow at least five minutes for
the oil to drain back into the oil pan. If you do
not do this, the oil dipstick might not show
the actual level.
If the engine has not been run long enough to
bring it up to normal operating temperature
and the oil is cool, turn off the engine and allow
30 minutes for the oil to drain back into the
oil pan. If you do not do this, the oil dipstick
might not show the actual level.
2. Pull out the dipstick and clean it with a
paper towel or a cloth, then push it back
in all the way.
272
Page 273 of 430
3. Remove the dipstick again, keeping the tip
down, and check the oil level.When to Add Engine Oil
If the oil is below the cross-hatched area at
the tip of the dipstick for the 6.6L V8 DURAMAX®
engine, you will need to add at least
two quarts/liters of oil. If the oil is below the
lower hole at the tip of the dipstick for the Isuzu
6H engine, you will need to add at least one
quart/liter of oil. But you must use the right kind.
This section explains what kind of oil to use.
For engine oil crankcase capacity, seeCapacities
and Speci cations on page 347.
Notice:Do not add too much oil. If the engine
has so much oil that the oil level gets above the
cross-hatched area for the 6.6L V8 (LLY) engine
or above the upper hole that shows the proper
operating range for the 7.8L L6 (LG4) engine,
the engine could be damaged.
6.6L V8 DURAMAX®Engine
Isuzu 6H Engine
273
Page 276 of 430

GM Goodwrench®oil of the recommended
viscosity grades meets all the requirements for
your vehicle.
Engine Oil Additives
Do not add anything to the oil. The recommended
oils with the API service symbol are all you will
need for good performance and engine protection.
When to Change Engine Oil (Vehicles
Without the Engine Oil Life System)
If you have the 6.6L V8 DURAMAX®Engine:
Change engine oil and filter every 15,000 miles
(24 000 km), or every 12 months, or every
750 hours of engine operation, whichever occurs
first. If you have the Isuzu 6H Engine: Change
engine oil and filter every 12,000 miles
(20 000 km), or every 12 months, or every
600 hours of engine operation, whichever occurs
first. SeeScheduled Maintenance on page 363.
Engine Oil Life System
(Gasoline Engine)
When to Change Engine Oil
Your vehicle has a computer system that lets you
know when to change the engine oil and filter.
This is based on engine revolutions and engine
temperature, and not on mileage. Based on driving
conditions, the mileage at which an oil change
will be indicated can vary considerably. For the oil
life system to work properly, you must reset the
system every time the oil is changed.
When the system has calculated that oil life has
been diminished, it will indicate that an oil change is
necessary. A change engine oil light will come on.
SeeChange Engine Oil Light on page 176. Change
your oil as soon as possible within the next
600 miles (1 000 km). It is possible that, if you are
driving under the best conditions, the oil life system
may not indicate that an oil change is necessary for
over a year. However, your engine oil and filter
must be changed at least once a year and at this
time the system must be reset. Your dealer has
GM-trained service people who will perform this
work using genuine GM parts and reset the system.
It is also important to check your oil regularly and
keep it at the proper level.
276
Page 278 of 430

Engine Oil Life System
(DURAMAX
®Diesel)
When to Change Engine Oil
If your vehicle has the Engine Oil Life System, it
has a computer system that lets you know when to
change the engine oil and filter. This is based
on injection timing, engine load and engine
temperature, and not on mileage. Based on driving
conditions, the mileage at which an oil change
will be indicated can vary considerably. For the oil
life system to work properly, you must reset the
system every time the oil is changed.
When the system has calculated that oil life has
been diminished, it will indicate that an oil change
is necessary. A change engine oil light will
come on. SeeChange Engine Oil Light on
page 176. Change your oil as soon as possible
within the next 600 miles (1 000 km) or 30 hours of
engine operation, whichever occurs first. It is
possible that, if you are driving under the best
conditions, the oil life system may not indicate that
an oil change is necessary for over a year.However, your engine oil and filter must be
changed at least once a year and at this time the
system must be reset. Your dealer has
GM-trained service people who will perform this
work using genuine GM parts and reset the
system. It is also important to check your oil
regularly and keep it at the proper level.
If the system is ever reset accidentally, you must
change your oil at 15,000 miles (24 000 km),
or 150 hours of engine operation, whichever
occurs first, since your last oil change. Remember
to reset the oil life system whenever the oil is
changed.
How to Reset the Engine Oil Life
System
The Engine Oil Life System calculates when to
change your engine oil and filter based on vehicle
use. Anytime your oil is changed, reset the
system so it can calculate when the next oil
change is required. If a situation occurs where you
change your oil prior to a change engine oil light
being turned on, reset the system.
278
Page 282 of 430

3. Store the seal in the inlet, located on the
underside of the hood
4. Store the clamp on the coolant surge tank.
Pull the overflow tube out of the white
plastic retainer, slip the clamp over and
reinstall the hose.
The seal will need to be replaced on to the air
cleaner for normal driving, especially in the
warmer months.
Automatic Transmission Fluid
When to Check
A good time to check your automatic transmission
fluid level is when the engine oil is checked.
See your Allison Automatic Transmission
Operator’s Manual to find out when to change
your transmission fluid and filters.
How to Check and What to Use
The Allison Automatic Transmission Operator’s
Manual that came with the vehicle shows how to
check the automatic transmission fluid and
what fluid to use.
Automatic Transmission External Filter
Your automatic transmission filter requires
periodic replacement.
Consult the Allison Automatic Transmission
Operator’s Manual that came with the vehicle for
proper change intervals.
282
Page 283 of 430

Manual Transmission Fluid
When to Check
A good time to have it checked is when the
engine oil is checked. Refer to the Maintenance
Schedule to find out when to check and change
your manual transmission fluid. SeeScheduled
Maintenance on page 363.
How to Check and What to Use
Check the fluid level only when your engine is off,
the vehicle is parked on a level place, and the
transmission is cool enough for you to rest
your fingers on the transmission case.
To check the transmission fluid level, do the
following:
1. Remove the filler plug.
2. Check to be sure that the lubricant level is up
to the bottom of the fill opening. On heavy
duty transmissions, an inch of oil level equals
about one gallon of fluid.3. If the fluid level is good, reinstall the plug and
be sure it is fully seated. If the fluid level is
low, add more fluid as described in the
next steps. Refer to the Maintenance
Schedule to determine what kind of fluid to
use. SeePart C: Recommended Fluids
and Lubricants on page 397.
How to Add Fluid
To add transmission fluid, do the following:
1. Remove the filler plug.
2. Add fluid at the filler plug hole. Add only
enough fluid to bring the fluid level up to
the bottom of the fill opening. Refer to
the Maintenance Schedule to determine the
proper fluid to use. SeePart C:
Recommended Fluids and Lubricants on
page 397.
3. Reinstall the filler plug. Be sure the plug is
fully seated.
283
Page 285 of 430

What to Use
Use a mixture of one-half clean, drinkable water
and one-half DEX-COOL®coolant which will
not damage aluminum parts. If you use this coolant
mixture, you do not need to add anything else.
{CAUTION:
Adding only plain water to your cooling
system can be dangerous. Plain water, or
some other liquid such as alcohol, can
boil before the proper coolant mixture will.
Your vehicle’s coolant warning system is
set for the proper coolant mixture. With
plain water or the wrong mixture, your
engine could get too hot but you would
not get the overheat warning. Your engine
could catch re and you or others could
be burned. Use a 50/50 mixture of clean,
drinkable water and DEX-COOL
®coolant.Notice:If you use an improper coolant
mixture, your engine could overheat and be
badly damaged. The repair cost would not be
covered by your warranty. Too much water
in the mixture can freeze and crack the engine,
radiator, heater core, and other parts.
If you have to add coolant more than four times a
year, have your dealer check your cooling system.
Notice:If you use extra inhibitors and/or
additives in your vehicle’s cooling system, you
could damage your vehicle. Use only the
proper mixture of the engine coolant listed in
this manual for the cooling system. See
Part C: Recommended Fluids and Lubricants
on page 397for more information.
285
Page 317 of 430

Other Service Items
Fuel Filter
Fuel Filter/Pressure Regulator
(Gasoline Engines)
The steel fuel filter/pressure regulator is located
near the engine compartment on the driver’s
side frame rail. If your vehicle has a rear steel fuel
tank, the fuel filter/pressure regulator is located
near the rear fuel tank, on the driver’s side frame
rail. SeeScheduled Maintenance on page 363
for recommended service intervals.
If your vehicle is equipped with the optional Davco
spin-on type filter, it is located on the driver’s
side frame rail.
Fuel Filter (Diesel Engines)
If you have a diesel engine, your fuel filter is
located in the engine compartment on the driver’s
side of the vehicle, or along the driver’s side
frame rail. See “Fuel Filter Replacement” earlier in
this section for further information.
Also seeScheduled Maintenance on page 363for
recommended service intervals.
Primary Fuel Filter and Water
Separator
If you have a diesel
engine, you may have
this spin-on filter. It
is located on the driver’s
side frame rail.
It has a clear plastic drain bowl at the bottom.
Check the drain bowl occasionally for any water or
particles.
To drain the bowl, do the following:
1. Shut off the engine.
2. Partially open the drain valve at the bottom of
the filter.
SeeEngine Oil (Caterpillar
®Diesel Engine) on
page 268orEngine Oil (Gasoline Engine) on
page 268orEngine Oil (DURAMAX
®/Isuzu Diesel
Engine) on page 272for proper disposal
procedures.
317