Mobil 5W-30??

Does it have any warranty left? I would feel guilty personally, making a claim when I knew I ignored the manufacturers recommendation.

Toyota recommends 0w-20 synthetic for every climate.

It certainly is going to get better gas mileage with the correct oil. What benefit do you hope for that precludes good gas mileage?

But it is your car, do what you think best, Toyota only designed it and built it, what do they know?

 

:thumb:

 

Nothing about 0W-20 here in the land of OZ, just the standard Japanese viscosity versus ambient temperature chart, nothing on the filler cap either.

 

OP is from Plano, Texas. While some might argue to the contrary, I do not think that is in OZ.

 

I've wondered that, too. 0W-20 obviously gives the highest mileage, but it seems like a very low viscosity for a Texas summer. I don't have any technical or inside knowledge about how the crankcase oil performs over different oil grades and temperatures.

 

There should not be an issue with 5/30 because there is a statement in the manual that says it is OK to use higher viscosity oils under certain severe driving conditions.

MB860 ?

 

None of us will ever know for sure but I strongly suspect the only reason 0W20 oil is recommended is to get a better fuel economy number on the EPA test. The EPA requires the same oil viscosity used for the test be the only oil viscosity recommended by the manufacturer.

However the engine is probably engineered well enough to survive on 0W20 oil indefinitely even in a warm climate. But I believe 0W30 or 5W30 would be a good choice at least in the summer. I have a long trip in the Southwest planned for this summer and I will probably use Mobil 1 0W30 instead of the 0W20 I have been using.

 

I live in the Southwest. I use 0W20 all the time. The temperatures can be down around zeroF in the Winter. In the Summer, they can easily exceed 100F.
Unless you plan on spending a lot of time in Death Valley in the summer, there would seem to be little reason to vary the the engine oil viscosity beyond the manufacturer's recommendation.

 

The temperatures in this part of Oregon are very similar to what you describe. Obviously 0W20 has worked for me so far as well as people who live in places like Phoenix, AZ. So I may stick with it, I'm undecided. But I do find it an interesting discussion point, unfortunately there is no good evidence supporting either point of view.

 

In 1982 I had a Honda Accord which called for as thin as 10W30 in the winter and 20W50 in the summer. At that time, that four cylinder Honda engine was considered technologically advanced. Today it is a dinosaur compared to the tighter clearances and operating temperature controls in the Prius. Regardless of the ambient temperature, the clearances inside the Prius engine don't change as much as the older cars so a single viscosity range covers all ambient conditions.

Consider this: at operating temperature, a 0W20 oil is 20 weight and a 0W30 oil is 30 weight; however, the engine was designed for 20 weight. 30 weight oil is thicker and will not flow as well through the engine. Reduced oil flow, especially to the valvetrain, will increase wear of those very expensive parts.

I think some folks want to use a higher weight oil because they still think that thicker oil gives better wear protection. This is no longer true. Some are tempted because the higher weight oil is a few bucks cheaper than the 0W20. This is penny wise and pound foolish.

 

Operating temp is much higher than ambient temp. So why would 100' air temp make 190' operating temp break down the oil faster?

 

Oil temperature is somewhat tied to air temperature, also to speed (airflow over the oil pan) and power output and water temperature. Engine oil temperatures usually run in the 200F to 240F range on a thoroughly warmed up engine on the highway.

The main variable between a hot place and a moderate climate, say 110F vs 80F is the amount of oil cooling through the oil pan. Some literature has suggested that engine oil temperature increases about 3 degrees for every 10 degrees of air temperature when driving in hot weather. That is a real squishy temperature ratio and will vary a lot. So, that means engine oil on a 110F day will run roughly 10F hotter that it will on an 80F day.

If you take 20 weight oil at 212F and compare it to 30 weight oil at 225F, they will be roughly the same viscosity. Those numbers are from memory, but are ballpark close. If someone cares to pull out some viscosity vs temperature charts they can easily check that.

 

I have been looking for information for the past few days, here is one of the best articles I have found on motor oil.

The author is an advocate of thinner oils, in fact he is using Mobil 1 0W20 in his Ferrari.

FerrariChat.com - FAQ: Motor Oil Articles by Dr. Ali E. Haas (AEHaas)

The article is 10 pages long with a test at the end, I think it's well worth reading if you have the time. After reading it I have decided to keep using 0W20, at least for now.

 

Thanks for this link. Very interesting. Pretty much correct. Except for one big thing. He doesn't know what viscosity he needs in his Ferrari in order to keep an oil film in the hydrodynamic journal bearings (mains & rods are typically journal bearings in most engines).

I still remember a very good article in the Porsche Panorama that pushed for multi-vis oils a few years back. They showed that with a straight 30 weight oil that they lost the oil film at oil temps around 300F. Now, mind you, if you lose the oil film at speed, you go metal to metal and the journal bearing quickly destroys itself. This article pushed for 20W-50 oil for the air-cooled 911 engines.

Fast forward to now and as the article you linked states, water cooled engines keeps the temps around 212 during winter and summer. This is where I disagree. I live in Phoenix and on my other car, which is water cooled, I've seen oil temps around 200 in the winter and up to 250 in the summer. Mind you, it gets HOTTER THAN HELL in the summer time here in Phoenix. Is 20 weight oil OK at 250F temps? Yes, but what if I'm pushing it hard and it gets to 275F? I'm not willing to test that, so I've always run 5W-30 here in Phoenix on a car I plan to push hard in the summer. The Prius? Doubt if I'm ever going to push that car so I'll probably be OK with 0W-20 oils. But I am also a firm believer that the reason the factory uses 0W-20 oils is for fuel economy. I used to run 5W-30 oil in my wife's old Accord V6 when it called for 0W-20. I may compromise and run a 0W-30 in the Prius, haven't decided yet since I haven't changed the oil yet. The interesting thing is my wife's new car, 2010 Mercedes C300 V6 calls for 0W-40. I'm sure Mercedes knows what it's doing , so why do they use 0W-40? I'm guessing they get less warranty issues with the thicker oil.

 

Thanks for the information. I wish oil temperature was available on the ODB-II but I don't think it is.

I think Mercedes has an arrangement with Mobil don't they? They probably also want an oil that meets the ACEA A3 specification and some of the oils Mobil sells in the U.S. are not rated A3. The 0W40 European Car Formula is one of their A3 rated oils. I used it in my BMW because they required an ACEA A3 oil also.

 

There is a fair amount of misinformation in Dr Haas's paper. Take it all with a big grain of salt.

 

To bad, it all sounds good to the uninformed, me. Well I'll keep searching for good information because I find it interesting. I suspect the Prius engine will last a long time on 0W20 or 0W30 either one.

I think one thing the good doctor has right, there is a lot of bad information out there about motor oils.

 

If you're really interested in answering these questions you don't have to guess. You can do oil analysis and prove whether or not the manufacturer's recommendations are best for your driving situation. A $15 kit will give you important clues as to the anti-wear anti-friction package the oil maker is using and will give you solid info on what's wearing and how much. For example, iron comes from cylinder walls and valve gear usually; nickel from intake valves; lead from main bearings, etc.

I did oil analysis every oil change on my Acura RSX because I didn't trust Honda's 5w-20 recommendation. I didn't trust the long oil change interval recommendation, and a couple other things. After 100,000 miles of analysis I found that the 5w-20 recommendation is solid and the long oil change intervals were really conservative.

 

One thing that hasn't been mentioned yet in this discussion is the on/off operation of the Prius ICE, whereas a conventional car ICE runs continuously. This is a huge difference and should cause the operating temperature of the Prius ICE to rise and fall and overall run cooler than a conventional ICE, even in hot climates. The ICE restarts many times in the course of a trip. Both of these factors should favor using the Toyota recommended 0W20 vs. a heavier weight.