Oil Weight in Hot Weather?

[Mike G.]

What weight does everyone run in the summer when the normal spec for the
Subie is 5W-30 oil? I've been going up to 10W-30 for July and August.

Mike

 

[mulder]

What weight does everyone run in the summer when the normal spec for the
Subie is 5W-30 oil? I've been going up to 10W-30 for July and August.

Mike

Either is ok, just follow the recommendations in the viscosity vs.
temperature chart shown in the owners manual.

 

[Mark H]

What weight does everyone run in the summer when the normal spec for the

Subie is 5W-30 oil? I've been going up to 10W-30 for July and August.

if 10-30 is "hot" weather.... then my car's getting pretty damned warm.
Usually gets 20-50w.

-mark

 

[mulder]

if 10-30 is "hot" weather.... then my car's getting pretty damned warm.
Usually gets 20-50w.

-mark

What car do you have? 20W50 is not recommended by Subaru for their
current vehicles.

 

[Edward Hayes]

My owner manual(2000 Forester) recommends 5w30 from 100 degrees down
and 10w30 above 40?. I use 10w30 because here in SW Fl my driving temp
is 85-95 digress which is in the very upper range for 5w30. The Subaru
recommendation also state you may go to a heaver oil IF you drive in
desert temp (120 degrees?) or pull trailer in mountains etc. Makes
little difference to me as to 5w or 10w because I use a Synthetic oil.
For a daily driver using dino oil I would go with the 5w30 unless
frequently driving in 90 degree + temperatures. I would not subject my
engine to a 15w 20wxxx oil. To much wear and lower gas mileage. JMHO
and Subaru's.

 

[John]

10w-30 except from Dec thru March, then its 5w-30 for those cold mornings.

 

[y_p_w]

What car do you have? 20W50 is not recommended by Subaru for their
current vehicles.

They currently recommend additional weights for towing or high temps.

From Page 11-18 of the 2004 Impreza WRX/WRX STi owner's manual:

"If the vehicle is used in desert areas, in areas with very high
temperatures, or used for heavy-duty applications such as towing
a trailer, use oil with the following grade and viscosities is
recommended.

API classification SL (or SJ):
SAE visvosity No.: 30, 40, 10W-50, 20W-40, 20W-50"

The basic reasons for these weights would be volatility issues
and/or excessive thinning at slightly higher oil temps. The
single weight oils are less volatile, while the heavier
multiweights will not be as thin.

A typical 20W-50 at 100°F is going to be thinner than a typical
5W-30 at 60°F. Even a lot of the "Group II" 30 weights are
essentially multiweights (maybe a 15W-30) but are marketed as
"heavy duty" gasoline engine oils.

 

[Rick Courtright]

What weight does everyone run in the summer when the normal spec for the
Subie is 5W-30 oil? I've been going up to 10W-30 for July and August.

Hi,

How hot does it get where you are?

I'm in a part of SoCal that regularly sees 100 deg F and up from late
June to mid-September, yet several people I know whose cars are rated
for 5W-30 run it all summer w/ no apparent ill effects. Personally I'd
be inclined to use 10W-30 as you're doing IF your book specs it for the
temp range you're likely to see, otherwise stick w/ the 5W-30.

Older cars generally seemed to have a much wider range of acceptable
grades than the newest ones. My '90 Loyale book says 5W-30 is acceptable
for severe winter use only, and then warns against prolonged highway
driving with it. 10W-30 is the "normal" grade, but 10W-40 and 20W-50 are
listed for temps such as I see in summer. Jump forward a few years and
it seems recommendations tightened up a lot when 5W-30 became fairly
standard. You might consider keeping that weight but going from dino oil
to synthetic if you haven't already?

Good luck!

Rick

 

[Guy Macon]

My owner manual(2000 Forester) recommends 5w30 from 100
degrees down and 10w30 above 40?. I use 10w30 because here
in SW Fl my driving temp is 85-95 digress which is in the
very upper range for 5w30. The Subaru recommendation also
state you may go to a heaver oil IF you drive in desert temp
(120 degrees?) or pull trailer in mountains etc.

Perhaps I can shed a bit of light on these recommendations.
I was the design engineer for a snap-on/Sun smog tester, and
am somewhat familiar with the physics of internal combustion
engines.

Lighter weight oils mean another mpg or two on the sticker and
for the customer. They also come in handy if someone who lives
in a hot climate takes a vacation where it is cold. Lighter
weight oils also mean more makes it past the rings, so you use
a bit more oil and put out a bit more smog -- but this is a tiny
amount on a modern automobile engine.

Heavier weight oils are good for an engine that has a lot of
slop, such as a Subaru with 200,000 miles on the engine or a
new Fiat 128 because it leaks and burns less.

A Subaru in the desert will not only see higher temps than
one in Florida, but it will see lower temps as well when someone
starts it at 5 AM, so clearly the 20W50 is *allowed* for our
Florida Subaru owner, but is it needed? The engine is likely to
still be tight, the temp outside won't get much above 100, and
there aren't any hills to climb, so I don't see any pressing
advantage to 20W50. 5W30 is also something that there is no
pressing advantage to using in Florida -- he won't be trying
to start it in a snowstorm. In my opinion, 10w30 is the right
choice.

I have a 1985 with 200,000 well-cared-for miles on it, I live
in Los Angeles, and occasionally go to Death Valley or Nevada,
so I use 20W50 and would use 30W60 if I could find it.

 

[Mike G.]

I'm in Denver. The summers sometimes get above 100 F but definitely into
the 90's for a month or two.

Mike

 

[Carl 1 Lucky Texan]

At one time, there were rumors that non-US modles of cars had higher
viscosity oil recomendations for the same engines as the US counterpart.
It was said this was due to the CAFE rules and gas mileage issues.

I wonder if anyone can compare - say - a Subaru, VW, Jaguar or other
vehicle's manuals from the US and another country?

Carl

 

[Losiho]

At one time, there were rumors that non-US modles of cars had higher
viscosity oil recomendations for the same engines as the US counterpart.
It was said this was due to the CAFE rules and gas mileage issues.

I wonder if anyone can compare - say - a Subaru, VW, Jaguar or other
vehicle's manuals from the US and another country?

Carl

My Australian Outback, built in Japan, has exactly the same viscosities
listed in the US owners manual, with the additional high load/temperature
viscosities listed by y_p_w earlier.

 

[Rick Courtright]

I'm in Denver. The summers sometimes get above 100 F but definitely into
the 90's for a month or two.

Well, considering 90's is plenty warm, and you can probably find a hill
or two to climb around Denver if you look real hard , I'd vote for the
10W-30 regimen you've already followed!

Rick

 

[Edward Hayes]

I live in SW FL. where the spring/summer/fall temp is in the 85-95
degree range. My Forest manual says 5w30 below 100 and 10w30 from +40?
to over 100 I also chose 10w30. I would use the 5w30 if most all my
trips were under 5 miles though.

 

[tom klein]

What weight does everyone run in the summer when the normal spec for
the Subie is 5W-30 oil? I've been going up to 10W-30 for July and
August.

Mike

getting back to basics, with a multi-viscosity oil, both numbers refer
to the oil's viscocity; the part before the "w" is the cold viscosity
and the part after is the hot viscosity.

so in warm weather, a 5w30 and a 10w30 are exactly the same, and so is
single-viscosity 30 weight. the big difference is in cold weather
(which just doesn't happen in florida), where 5w30 is a lot easier to
start with, since it behaves like a 5 weight single-viscocity oil.
subaru's recommendation probably isn't based on more protection on the
hot end of the scale, but on easier starting at the cold end, because
in either case, once the oil is hot, all you get is the protection of a
30-weight oil.

before multi-viscosity oils, it made sense to switch from 5 in the
winter to 30 in the summer, and back, for example. but most people
today would rather pay a bit more for multi-viscosity than change oil
twice a year.

for better heat protection, or less leakage, a heavier oil than
30-weight might be good, such as 10w40, but it will probably increase
fuel consumption.




........ tom klein

 

[y_p_w]

getting back to basics, with a multi-viscosity oil, both numbers refer
to the oil's viscocity; the part before the "w" is the cold viscosity
and the part after is the hot viscosity.

Not exactly. The "W" number states a requirement for cold pumping and
cold cranking at certain temperatures. The requirements for a 5W-XX
oil are at -30/-35°C. For a 10W-XX, the requirements are at
-25/-30°C. The second number represents the acceptable viscosity
rage at the SAE "standard" operating temperature.

so in warm weather, a 5w30 and a 10w30 are exactly the same, and so is
single-viscosity 30 weight. the big difference is in cold weather
(which just doesn't happen in florida), where 5w30 is a lot easier to
start with, since it behaves like a 5 weight single-viscocity oil.
subaru's recommendation probably isn't based on more protection on the
hot end of the scale, but on easier starting at the cold end, because
in either case, once the oil is hot, all you get is the protection of a
30-weight oil.

Not in "warm weather", but at "operating temperature". The caveat
is that depending on the car and ambient conditions, the oil could
exceed the SAE's 100°C operating temperature, and the viscosity goes
down. A typical 5W-30 oil is going to be thinner than a typical
10W-30 oil at most ambient temps. However - there are exceptions.
the latest Mobil 1 5W-30 is actually rated a tad thicker than their
10W-30 at 40°C (~105°F). A 0W-40 oil is going to be thicker at
summer ambient temps.

<http://www.mobil.com/USA-English/Lubes/PDS/GLXXENPVLMOMobil1_0W-40.asp>
<http://www.mobil.com/USA-English/Lubes/PDS/GLXXENPVLMOMobil1_5W-30.asp>
<http://www.mobil.com/USA-English/Lubes/PDS/GLXXENPVLMOMobil_1_10W-30.asp>

Not all XW-30 weight oils are the same. There are some that tend
towards the thick side of 30 weight. Some 0W-30 oils are too thick
to meet the API "Energy Conserving" standard. The newest Mobil 1
5W-30 is actually thicker than their 10W-30 at 100°C. The German
made version of Castrol Syntec 0W-30 borders on being a 0W-40.

Also - I've heard from some people with oil temp gauges that their
oil doesn't even reach full operating temperatures until about 15-
20 miles on the highway. A multi-vis oil has the advantage that
it's typically going to flow better during this period and provide
less drag to the engine with better fuel economy.

before multi-viscosity oils, it made sense to switch from 5 in the
winter to 30 in the summer, and back, for example. but most people
today would rather pay a bit more for multi-viscosity than change oil
twice a year.

for better heat protection, or less leakage, a heavier oil than
30-weight might be good, such as 10w40, but it will probably
increase fuel consumption.

Depends on a number of factors - especially if there's an oil to
coolant heat exchanger - i.e. oil cooler. Part of the reason for
the recommendation of a "heavier" weight oil is because at high
ambient temps the the ability of the cooling system to keep the
oil at standard operating temps isn't as good. A typical 5W-30
oil might be too thin if the oil temps are 240°C, while the
20W-50 that would rob power at 200°C will be thicker. A factory
oil cooler should regulate oil temps near that of the thermostat.

There's a lot more that hasn't been touched. Oil volatility, high-
temperature/high-shear viscosity. Viscosity index improvers. Shear
stability. Ability to stay in grade. Sludge protection.