Rule of thumb... Change it often, and any high-quality oil of the
appropriate viscosity rating should do fine. I have also heard tales of
synthetic oils eating through seals on older cars. Anybody want to
confirm or debunk this?
Andy Ramm
'67 Midget Mk III -- The Smidgin
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Everyone has an opinion about motor oil. Talk to 10 different people
and you will hear 10 different suggestions for brand and grade.
Unfortunately, these opinions are not usually based on the facts. I
do not consider myself an expert on the subject, but I have studied
about it and will tell you the facts I do know.
1) The Society of Automotive Engineers (SAE) tests motor oils and grades
their viscosity / thickness (i.e. the SAE rating). The higher the
number, the
heavier the oil. Therefore, 10W-30 is a thinner oil than 20-W50.
Also, the W in the SAE rating means that it has been tested at 0
degrees F (W = Winter) to see that it still flows well when cold. The
SAE also
tests these oils at 210 degrees F.
This rating is to be used as a guideline for choosing your oil
viscosity. Basically, you want a thinner oil (lower SAE rating) for
winter because oil will tend to gel when cold. However, in the
summer you want a heavier oil because it will flow better at higher
temps. Select your oil based on the temperatures you expect to drive
in before your next oil change.
Most auto owner's manuals include a chart suggesting the best oil
choices. You certainly can veer from these suggestions, but you
can't really go wrong if you follow their advice.
There are, of course, other things to consider. For example, a lighter
oil will
give you slightly better mileage (that is why GM recommends 5W-30
almost exclusively now). GM reported a mileage improvement of 3 mpg.
when they switched frmo 10W-30 to 5W-30. I don't know if I believe
that, but this is what they announced.
2) The next point to consider is the API rating (American Petroleum
Institute). This is basically a rating of the quality of the oil
mixture. Bearing in mind that up to 20 % of your motor oil is
comprised of cleansing and other non-oil compounds, it is important to
go for high quality mixtures.
The API ratings come in 2 types - S for spark ignitions (Gas engines)
and C for compression ignitions (Diesel engines). The S ratings go
from SA to SH (SH is the highest and newest oil rating).
The API guys test the following factors :
- Cold Starting and Pumpability
- Rust and Corrosion
- Fuel Economy
- Phosphorus Content
- Deposit Test
- High Temperature Thickening
- Engine Wear
The differences between letters is quite significant. For example,
SH arrived about 1 1/2 years ago and offers the following
improvements over SG rated oil .
SH improvements over SG
- 13 % less bearing wear
- 17 % less cam and lifter wear
- 3 % less engine rust
- 9 % less engine sludge
- 5 % less engine varnish
- 7 % improved fuel economy !!!
- 21 % less high-temp oxidation
- 7 % less piston varnish
Therefore, you should check that the oil you use has the SH rating.
Also, don't worry that your manuals call for SG or lower ... better
oil can only be better for the car.
Also, look for the API symbol on the oil container (a large gear
showing that the oil is API certified).
3) Check for the fuel economy rating on the oil. The current "best"
is Energy Conservation II. This is key because Energy Conservation I
and non-Energy Conservation are still being sold today (cheaper for
the gas stations to buy, therefore more profit for them).
*********************************************************
Overall - what does this mean? Good question ...
Basically, you should always buy good quality oil. However, as long
as the ratings are as listed below, the brand is basically not critical.
Check
the following :
Proper viscosity (SAE) for your car / weather / driving habits, etc.
Top API quality rating (SH)
Top Fuel Economy (Energy Conservation II)
Follow these suggestions and change your oil at least as often as
your manual suggests, and you shouldn't have problems.
If this information helps anyone out there, please just drop me a
note. Thanks !
Ira M. Weinstein
BTW - Synthetic oils are another interesting subject. If anyone out
there wants me to write up something about Synthetic oils (again,
based on the facts), just drop me a note.
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