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2009 Forester
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Discussion Starter #1
We have an 09 Forester non-turbo with about 8000 miles on it. We live in Tucson, AZ - it's pretty hot here in the summer. Manual states 20w 50 oil is a good choice in desert climates or hard use. Any downside?
 

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2017 VW Golf SportWagen 5MT
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That's pretty thick oil for a new car. Maybe 5w40 if you wanted to go thicker? 20w50 is pretty old-school, oil formulas have advanced quite a bit in recent years.

Stan
 

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2015 Highlander AWD XLE 6AT
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4,255 Posts
Yeah, it can get hot in Tuscon! See the attached chart.

20W-50 is just one of the oils recommended by Subaru for desert or high temperature operation ('09 OM pages 11-11 and -12):

*: 5W-30 is preferred.

Engine oil viscosity (thickness) affects fuel economy. Oils of lower viscosity provide better fuel economy. However, in hot weather, oil of higher viscosity is required to properly lubricate the engine.

Recommended grade and viscosity under severe driving conditions

If the vehicle is used in desert areas, in areas with very high temperatures, or is used for heavy-duty applications, use of oil with the following grade and viscosities is recommended.

API classification SM (or SL):
SAE viscosity No.: 30, 40, 10W-50, 20W-40, 20W-50​

I'd agree that 20W-50 engine oil may be a tad thick for a young engine in a passenger car. However, considering Tuscon's summer temps, I'd probably consider 20W-40 in the summer (~May through ~September), and then switch back to 10W-30 for the other eight months.

HTH,
Jim / crewzer
 

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2008 Forester X Premium 5MT
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8,070 Posts
I am in agreement with the above posters. With 20w50 you are going to see increased wear on start up as it will take a longer time for the oil to reach the critical areas of the engine. I would also suspect your oil pump would be bypassing a lot of oil needlessly as it tried to push the oil.

As said with current oil formulas there are much better options you can look at that will handle the high heat and heavy use much better then 20w50 will while seeing less wear.

In reality any oil with out the "Energy conserving label" should do just fine, valvoline max life comes to mind.

If you want/must use some thing other then a 5w30/10w30/10w40 for what ever reason look at a 5w40/5w50/10w50 as possible options.

You may also want to ask this question on a forum like bobistheoilguy.com but be prepared to learn
 

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WAY too thick.

Unless you're towing the max load and really beating on the car you shouldn't need anything close to that.

If you want something heavier than the oem specced 5w30, you might want to try a 5w40, but I don't think I would go any heavier than that, especially on a new engine.

If you were racing the car in that heat, maybe a 15w50 would be called for, but I doubt you'll be putting that much stress on it to require such a thick oil.
 
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