Oil--10w30 Or 10w40 In Hot Weather?

[flyted]

My owners manual says if temps are to remain above 0F and expected temps to 100F, use 5 or 10w30. If you go to the Hyundai hmaservice site, it says if temps over 100F, 10w40 would be appropriate. I called both the dealer and the 800 customer service number to ask why the difference and which one to use. Temps will be 110+F on my travels, so it is a honest question, not just being nit-picky. Both said they don't know why the difference, just use 10w30 since its in the manual. My concern is that in this small 2.0L 4cyl, high revs and high temps may need the 10w40 for proper protection and I won't be using it. I'll be doing some light off-roading which makes it worse with less airflow. Hyundai should have been able to give me an answer.

[duke]

I use (and strongl recommend) Castrol Syntec 5W40 (full synthetic oil) in my V6 Sonata for all-year-round use. As you know, Canada can get blooooody coooooold. I did this with my old 1990 Sonata, which lasted 436K km, without engine repairs, not even lifters. I always do my oil changes every 10K km (6K miles), and so do many others on my recommendation, and all their cars engines achieve trouble free high mileage.

[Atti_5]

[b]My owners manual says if temps are to remain above 0F and expected temps to 100F, use 5 or 10w30. If you go to the Hyundai hmaservice site, it says if temps over 100F, 10w40 would be appropriate.
My concern is that in this small 2.0L 4cyl, high revs and high temps may need the 10w40 for proper protection and I won't be using it.* Hyundai should have been able to give me an answer.

Yes, they SHOULD have

Please DEFINITELY GO with [b]10w40 - if not with 10w50 !!!!

The recommended temperature range are as follows

10w30: -13 F to 100 F (-25Celsius to 38Celsius)
10w40: -13 F to no limit (-25Celsius to no limit)

In other words the difference between the two oils You are hesitating is, the 10w40 has same performance at low temperatures, but works well also above 38C/100F

Attention!
[b]5w40 is for cold climate !!! only below 68F/20C

Source HMA table - Recommended SAE viscosity number by temp.

[rod lang]

Atti, hello from Montreal Canada.

There is no difference between 5W40 and 10W-40 in hot weather as the viscosity index improvers are the same for both oils. Both give equal protection at higher temperatures with the 5W-40 having a better advantage of faster lubrication in sub zero temperatures. My choice for our Canadian winters and fairly hot summers is Mobile One full synthetic 5W-30. I run my wife's 2.7 awd on this and my 4.7 Tundra pickup which now has over 300,000 of trouble free kms. on it. Most newer models that are coming out recommend 5W-20 year round. Remember, everyone is trying for improved gas mileage and thinner oils produce less friction overall, the additives these days give better overall protection than oils five years ago. Thinner oil also cools the engines better. Boil some water then some molasses, which looses its heat faster ?
Rod.