===========DO NOT USE AUTOMOBILE MOTOR OIL. YOUR TRUCK CALLS FOR DIESEL RATED
MOTOR OIL, CI-4. ALMOST NO AUTOMOTIVE OILS ARE RATED CI-4. THE
DIESEL RATING IS NEEDED TO DEAL WITH COMBUSTION BY-PRODUCTS UNIQUE TO
Your truck calls for 15w-40 oil, with a CI-4 rating. The alternative
is 5w-40 with a CI-4 rating, which appears to be what you are looking
for. The 5w-40 can be used year round as most are synthetics, and is
better for cold weather starts.
These oils should be available at stores such as WalMart.
Brands to look for , 15w-40, include Shell Rotella, Mobil Delvac 1300,
Chevron Delo 400, etc. Just look for the CI-4 rating. Most 15w-40
oils have it, as this viscosity range is for diesels.
In 5w-40, you can look for Shell Rotella Synthetic, and Mobil 1 Truck
and SUV. My local WalMart carries both. The Rotella Synthetic comes
in gallon jugs, the Truck and SUV in 5 quart jugs.
The 5 quart jugs are especially convenient, as two jugs is the engine
According to my Duramax owner's manual, 15w-40 and 10w-30 are both rated for
the same low temperature range (0F) but 10w-30 tops out at 100F. For temps
lower than 0F, the book says to use 5w-40 and if I were in your shoes then
that's the oil I'd use.
The '04s call for either CI-4 or CH-4, but the '05s MAY only require CI-4.
My personal preference would be to stick with a synthetic, and use the 5w-40
from around November to April.
Cheers - Jonathan
============I have an 03 Duramax with the LB7 engine. This engine does not have
EGR, and the manual calls for CH-4 or CI-4. I am not sure what is in
the manual for the 05 either, but the 05 uses the LLY engine that has
EGR. The difference between CH-4 and CI-4 is that the CI-4
certification test includes parameters specifically relevant to EGR
engines. So I would use CI-4 for an 05 EGR equipped engine, even if
the owner's manual still said CH-4 or CI-4.
Actually, at this time, all of the "real" diesel motor oils, such as
Rotella, Delvac, Mobil 1 Truck and SUV, Chevron Delo, etc. have the
CI-4 rating, and some even have a CI-4+ rating.
========The principal thing in the CI-4 rating is the capability to keep soot
in suspension, which is important for diesels, particularly the EGR
diesels, but not relevant to gasoline engines.
If the soot gets out of suspension, it can coke up/sludge up an
The other thing you see in the specification is the Total Base Number,
or "TBN" of the CI-4 oils is much higher than the TBN of automobile
oils that may have a CF rating. Total base numbers of the top of the
line diesel CI-4 oils is around 12, and for the really, really top
oils used for super heavy duty construction equipment, I have seen as
high as around 14. On the other hand, for gasoline engine oils that
otherwise meet SL, it is usually under 10.
This represents the ability of the oil to handle acid combustion
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