How to Choose the Right Oil (Taken from The Motor Oil Bible)
This is probably the number one question that I receive from people. “How do I
know what oil to use for MY vehicle?” There are actually a number of preceding
questions you need to ask yourself long before you can effectively answer this
more general, but extremely important, question.
Motor oil is the most important component of your engine. Without it, your
engine dies. With the wrong oil, your engine dies slowly. Getting it right really
does matter. Use this guide to help you make the best selection possible so that
you can get as much life as possible out of your engine.
MOTOR OIL TYPE
First and foremost, do not overlook the fact that viscosity is not the only criteria
critical to proper motor oil selection. You must choose an oil that is matched to
your application with regards to it's formulation and design, specifically
basestocks and additives used. For example, if you are running a diesel engine,
then you had better be sure the oil you choose is rated for diesel engines.
Similarly, if you are running a gas engine, then the oil should be formulated for
use in gasoline engines.
Of course, sometimes, an oil can be rated for both gas and diesel use. However,
your oil should meet at least the minimum API specifications required for YOUR
vehicle. For instance, if your vehicle manual calls for an API SL oil (which is a
gas engine oil specification), then your oil should specify that it meets/exceeds
that minimum standard (in other words, it should be rated for API SL, SM, ...). It
MAY meet other specifications as well, but it MUST, at a minimum, meet the API
SL specification.
Likewise, if you are running a diesel engine and your owner's manual specifies
that you should only use API CI-4 oils, then you should not use an oil that is
only rated for CH-4. This is not a recent enough specification. However, if the oil
you are considering indicates that it meets API CJ specs, then you're ok, since “J”
comes after “I”. API specs are generally “backwards compatible”, meaning that
the CJ spec also is appropriate for use in vehicles calling for CI, CH, CG, CF, etc.
(all PREVIOUS API diesel classifications).
Moreover, some vehicle manufacturers will specify OEM specific ratings that an
oil must also meet. This is more common with European vehicles, but is
becoming more common with US manufacturers as well. So, if your owner's
manual says that your oil is to meet BMW specification XYZ123, then you had
better make sure that the oil you're considering indicates that it meets that OEM
spec.
SYNTHETIC OR PETROLEUM
This is a question that is actually a relatively critical one IF you have any concern
over how long your vehicle/engine should last. There are plenty of situations
that do NOT warrant the use of synthetic oil, and you may very well be in one of
those situations, depending upon your vehicle, how you drive, where you drive
or how long you intend to keep your vehicle. Of course, it is just as likely that
your situation may very well warrant the use of synthetic oil, and the decision
regarding which you should choose is not necessarily a simple one.
The truth is, there are MANY variables that affect this decision, not the least of
which is just how much trust you put in a synthetic oil to offer enhanced
protection and possibly extended oil drains. Some of the many benefits that
synthetic oils offer can only be taken full advantage of if you actually trust them
to offer those benefits and push the oils beyond what a conventional petroleum
oil could accomplish.
By now, if you've read the preceding chapters of this book, you already know
what you need in order to make an educated decision in this regard.
THE VISCOSITY QUESTION
In most cases you can simply go with the manufacturer's recommended viscosity
grade. Of course, if you're considering a synthetic oil, it is generally very safe to
go to a lesser “w” rating than what is recommended by the manufacturer
(although the higher the quality of the synthetic, the more true that statement is).
For instance, if the manufacturer recommends a 10w30 viscosity (and isn't
already specifying the use of synthetic oil), then you would be safe to use a 5w30
or 0w30 synthetic oil.
Generally (see below for exceptions), if the vehicle manufacturer specifies an
XwY viscosity oil (such as 5w30, where “X” is “5” and “Y” is “30“), under most
circumstances you should stick with the same “Y” value, but can go to a lesser
“X” value to improve cold weather performance and possibly fuel efficiency.
However, in my opinion, you should ONLY do this if you're moving to a
synthetic oil and synthetic is NOT already being specified by the vehicle
manufacturer.
In other words, if your vehicle manufacturer is calling for a 10w30 SYNTHETIC
oil, then, although you MAY be able to go to a 5w30 synthetic oil, I, personally,
would not recommend it without some significant investigation into the issue.
On the other hand, in nearly all cases, if the vehicle manufacturer is calling for a
10w30 oil and does NOT specifically indicate that you should use a synthetic oil,
then, you should be able to EASILY move to a 5w30 synthetic oil, and possibly
even a 0w30 synthetic oil with no trouble at all.
If the manufacturer specifies multiple viscosities that can be used in your vehicle
but does NOT specify the need to use synthetic oil, then a petroleum oil of ANY
of those listed viscosities would be fine, although, the conditions under which
the vehicle will be driven would dictate whether to stay at the “high end” or
“low end” of the viscosity range listed.
Will you be driving in cold temperatures mostly? Go with a lower viscosity.
Congested city driving where engine temps can rise considerably? Heavy
towing (same heat issues)? Do you live in a very hot climate? Stay at the higher
end of the scale.
All of these and other driving conditions should be taken into account in trying
to find the BEST viscosity for your application. However, ANY of the listed
viscosities should be adequate, even if using petroleum oil, since the
manufacturer is not specifying synthetic as being mandatory.
In contrast, if the vehicle OEM is NOT specifically calling for synthetic, but
you're planning on going that direction, then, nearly always, you can safely stick
to the lowest “Y” value listed and could even go to a LOWER “X” value. So, for
instance, if the manufacturer said you could use 10w30 or 10w40 in your vehicle,
unless your application falls under one of the exceptions below, you could safely
stick to an Xw30 oil (using the lowest “Y” value listed) and you could go with a
0w30 or 5w30 oil safely, even though the manufacturer listed only 10w options.
Don't Thicker Oils Offer Greater Protection?
The cop-out answer is SOMETIMES. Thicker isn't always better - even when
using a petroleum oil. Although it is true that heavier viscosity oils (which are
generally thought of as being “thicker”) will hold up better under heavy loads
and high temperatures, this doesn't necessarily make them a better choice for all
applications.
NOTE: When I refer to higher or heavier viscosity oils, I'm referring to the
“second” number of a multi-viscosity specification. In other words, a 10w40
would be heavier than a 10w30 because 40 is higher than 30. I'm not making any
reference to the “w” rating because this doesn't come into play unless you're
referencing cold temperature performance.
You see, on many newer vehicles only 5w30 or 10w30 motor oils are
recommended by the manufacturer. If you choose to use a higher viscosity oil
than what is recommended, at the very least you are likely to reduce
performance of the engine. Fuel economy will likely go down. Engine
performance will likely drop.
In the winter months I would highly recommend that you not use a heavier
grade oil than what is recommended by the manufacturer. In cold start
conditions you could very well be causing more engine wear than when using a
lighter viscosity oil. In the summer months, going to a heavier grade is less of an
issue, but there are still some things to be aware of.
Moving one grade up from the recommended viscosity is not likely to cause any
problems (say from a 10w30 to a 10w40 oil). The differences in pumping and
flow resistance will be slight. Although, as was mentioned, efficiency of the
engine will decrease, the oil will likely still flow adequately through the engine
to maintain proper protection, and, under certain circumstances (heavy load,
high RPM), you MAY see improved protection with this heavier oil.
Moving two grades up from the recommended viscosity (say 10w30 to 20w50) is
a little more extreme and could cause long term engine damage if not short term.
Here's the thing. Although the oil will still probably flow ok through the engine,
it is a considerably heavier viscosity oil. As such it will be more difficult to pump
the oil through the engine.
More friction will be present than with a lighter viscosity oil. More friction
means more heat. In other words, by going to a heavier weight oil, you may
actually be causing more heat build-up within the engine. You'll still be
providing adequate protection from metal to metal contact in the engine by
going with a high viscosity, but the higher viscosity will raise engine
temperatures.
Over the short run, this is no big deal. However, over the long term, when
engine components are chronically run at higher temperatures, they WILL wear
out more quickly. As such, if you intend on keeping the vehicle for awhile, keep
this in mind if you're considering using a heavier weight oil than the
manufacturer recommends.
The key is to generally stay away from viscosity grades that are not mentioned
in your owner's manual. Sometimes vehicle manufacturers will make reference
to the possibility of using a 10w40, 15w40 or 20w50 motor oil, even though they
might recommend a lighter weight oil for most situations.
If this allowance is made, you'll be ok using a heavier grade of oil. You'll
probably see a drop in mpg using the heavier oils, but you will not likely cause
any long term engine problems. I would recommend, however, to stick with the
lower weight recommendations if using a synthetic oil, even if you're running
the engine in higher temp climates. I think you know why by now.
If the manufacturer does not make allowance for heavier weight oils, it would be
my recommendation that you DO NOT use a heavier weight oil in your engine.
Under most circumstances, stick with a viscosity grade that is recommended by
the manufacturer. And, if you do choose to use a heavier weight oil, at least
make sure that you only move up one grade. Never move up two grades.
Exceptions to the Above Rule
1. If yours is a racing application, more investigation would be necessary to
determine the proper viscosity to be using in your engine.
2. If yours is a heavy duty application where your vehicle is being subjected
to EXTREME service such as towing extremely heavy loads, you may
want to consider going to one of the heavier recommended viscosities.
3. If you are not comfortable venturing outside of OEM viscosity
recommendations, then, by all means stick with what your vehicle
manufacturer recommends. OEM viscosity recommendations will be
perfectly safe for your vehicle and will make your selection process easy.
Specialized Cases
It is possible, depending upon how you are using your vehicles or equipment,
that a more extreme divergence from the OEM viscosity recommendation might
be appropriate. However, if you think this may be the case, before making the
decision to diverge entirely from the manufacturer's viscosity recommendation,
please do your homework.
MOTOR OIL QUALITY COMPARISONS
Once you've managed to decide the type and viscosity of oil you should
probably be using, the question then comes down to determining which of the
oils that meet your criteria are the best of the bunch. In most respects, the only
way to really make that determination is to check the specs. It's not a perfect
technique, since the specs can “lie” in some ways, but, it's the best option you've
got.
