Oil Weight in Hot Weather?

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

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

Reply to
mulder

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

-mark

Reply to
Mark H

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

Reply to
mulder

Reply to
Edward Hayes
10w-30 except from Dec thru March, then its 5w-30 for those cold mornings.
Reply to
John

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.
Reply to
y_p_w

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

Reply to
Rick Courtright

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.

Reply to
Guy Macon

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

Mike

Reply to
Mike G.

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

Rick Courtright wrote:

Reply to
Carl 1 Lucky Texan

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.

Reply to
Losiho

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

Reply to
Rick Courtright

Reply to
Edward Hayes

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

Reply to
tom klein

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=B0C. For a 10W-XX, the requirements are at

-25/-30=B0C. The second number represents the acceptable viscosity rage at the SAE "standard" operating temperature.

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=B0C 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=B0C (~105=B0F). A 0W-40 oil is going to be thicker at summer ambient temps.

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=B0C. 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.

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=B0C, while the

20W-50 that would rob power at 200=B0C 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.

Reply to
y_p_w

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