You have to think about your climate.
Cold Temperatures in colorado effect engine performance.
In order to start effectively, engines must reach a critical cranking
speed. As temperatures drop, achieving critical cranking sped becomes
more of a challenge. Low temperatures cause motor oils to thicken, and
if they thicken too much and impose excessive drag on moving parts,
critical cranking speed will not be achieved and the engine will fail
Motor oils used in winter climates must maintain a sufficient low
cranking viscosity to allow engine turnover at the lowest
temperatures. If a motor oil is able to meet the challenge of allowing
the engine to turn over, it immediately faces another significant
challenge: providing quick, critical lubrication to the engine?s
bearings and other moving parts.
Two types of engine pumping failures can result from cold-thickened
motor oil: air-binding failure and flow-limited failure. Air-binding
failure occurs when the motor oil surrounding the pump inlet screen
gets sucked into the pump, but is not replaced by new oil from the
sump. The oil pump inlet screen then becomes starved for fluid, and
oil pressure becomes erratic as air is entrained and proper oil flow
cannot b e maintained. Flow-limited failure occurs when the motor oil
becomes so thick that it cannot be pumped through the inlet tube and
through the narrow passages that deliver the oil to the engine?s
All motor oils thicken in cold temperatures, but how much they thicken
is significant to the level of protection an engine receives. Pour
point tests (ASTM D-97) pinpoint the temperature at which a motor oil
thickens to the point where it ceases to flow. Of course, when oil
stops flowing altogether, it is useless. For an engine to receive even
minimal wear protection from an oil, it is important it has a pour
point lower than typical winter temperatures.
Conventional motor oils face significant challenges in low
temperatures because they contain paraffinic (wax) materials. As
temperatures drop, the wax components crystallize and agglomerate into
Eventually, the motor oil gels, becomes resistant to flow and fails to
provide the engine with the lubrication it needs. In order to hinder
the development of these wax crystals, conventional motor oils are
additized with polymers known as pour point depressants. These pour
point depressants prevent wax crystals from agglomerating and can
lower the oil?s pour point. In fact, petroleum motor oil without
additives typically has a pour point only around 5 degrees F, but the
inclusion of pour point depressants can lower the pour point by
approximately 25 degrees.
Synthetic motor oils do not contain the paraffinic material present in
conventional motor oils, so they do not require pour point additives.
Synthetic motor oils naturally flow at much lower temperatures than
conventional oils, maintaining their cold-temperature protection over
a longer period of time.
Cold weather operations also increases problems associated with
condensation. The colder the weather, the longer it takes for the
engine to warm to the point where condensation evaporates. During
short trips, the engine may not have a chance to evaporate the
condensation at all. Eventually, condensation causes acids to form in
the oil causing corrosion.
Rust and corrosion inhibitors serve to neutralize and protect engines
against water and acids. The oil-soluble additives have a greater
affinity for metal than water, forming a protective film on engine
parts. The Total Base Number (TBN) of a motor oil is an indication of
how well it combats acids. The higher the TBN number, the greater the
degree of protection.
AMSOIL Motor Oils are formulated with high TBN. In fact, AMSOIL 5W-30,
10W-30 and 0W-30 Motor Oils all have TBN?s over 11, allowing them to
effectively fight acid and corrosion for extended drain intervals.
AMSOIL Synthetic Motor Oils remain fluid in the coldest operating
conditions. Maintaining their fluidity and protecting ability in
temperatures as frigid as -60 degrees F, AMSOIL not only permits easy
engine cranking for quick starts, but flows to critical engine
components in a quarter of the time that conventional oils take.
Considering that up to 60 percent of all engine wear occurs during
cold starts, this immediate lubrication is essential to long-term
Now for the summer time....
your average temps are in the high 60's. So I would switch to a 10W20,
just perfect for your climate and engine milage in the late
spring.Whereas if you had warmer summers you would need to switch to a
thinner oil in the late spring. Like a 10W30 or 40.