0w-40 oil in a 140K miler?

Before you do the change over get a used oil analysis. If your Mobil 1 is showing good wear, good TBN and has not sheared the viscosity too bad the 5W30 is fine. The 40 weight would give less MPG and would not help unless you were losing oil between changes from engine wear.

Wayne

 

Agreed. If you suspect the motor has been poorly maintained, a used oil analysis is essential

The Mobil 1 0W-40 European Car Formula is an excellent oil, and I use it in my FJ Cruiser. It's considered a "light" 40, so there should be minimal impact on fuel economy compared to Mobil 1 5W-30

 

Actually, the manual for the EU market Prius suggests up to a 20W-50, depending on ambient conditions. In the EU, a 0W-40 is a very popular choice for extended oil changes and engine protection, with minimal impact on fuel economy

Indeed, many Opel, BMW, and Mercedes models require a 0W-40 for their extended service intervals of up to 24 months or 30,000 miles

 

Since you are approaching winter, its not clear that 40 weight oil will help unless your engine has problems with oil consumption. However this is a good experiment for you to try.

Should you find that you experience engine no-start problems in the winter (i.e., DTC P3191), I suggest switching back to xW-30 oil.

 

No, no, no!

Always stick with the thinnest grade of oil recommended in your car's manual. You will get the maximum gas mileage and longest engine life.

Once you make the switch to a thicker oil grade, there is no going back to a thinner grade. Thicker oil means higher oil pressure. Higher oil pressure means your cylinder rings, valve seals, and various other seals in your engine will endure higher pressure, and this will permanently deform them. Not only that but tolerances of metal parts in your engine will also change and adjust to higher oil pressure. All this change is bad, and it will result in increased oil consumption, more engine noise, and, the worst part, less smooth engine performance. At the end the overall result is to decrease the life of your engine.

It's a myth that thicker oil grade will decrease oil comsumption in high mileage cars. The truth is it won't. Although thicker oil passes through tiny gaps more slowly for a given oil pressure, increased oil pressure caused by thicker oil compensates for this and you get similar or more oil consumption when you switch to thicker oil.

Perhaps the only exception could be during summer months in hot deserts where your engine runs much hotter than otherwise. Then, if you switch to a thicker grade, say from 0W-30 to 0W-40, during extreme heat, such 100+ F temperatures, you might see a benefit. This is because increased temperature will thin your oil, and 0W-40 in a very hot engine will behave like a 0W-30 in a normal-temperature engine. But do this only if a thicker grade is recommended for such high temperatures in your owner's manual. If not, your cooling system is powerful enough that your engine temperatures don't change much under extreme heat and you should use the same grade during very hot weather.

So, the bottom line is that always stick with the thinnest oil recommended in your owner's manual throughout the life of your car, no matter how many hundred thousand miles you have on it. The only exception would be if a thicker grade is allowed for extremely high temperatures in your owner's manual. In that case you can switch to the next thicker grade during 100+ F or so weather, or more accurately, whenever your engine-temperature gauge shows higher than usual engine temperatures, but still avoid very thick grades such as 20W-50.

One other note: If your manual recommends 10W-30, you can always use 5W-30 or 0W-30 in all temperatures. Likewise if your manual recommends 5W-30, you can always use 0W-30, and if it recommends 5W-20, you can always use 0W-20, regardless of the temperature. Using 5W- instead of 10W- or 0W- instead of 5W- oil will increase your gas mileage and extend your engine life. Decades ago 5W-30 oil was not recommended for very high temperatures but modern motor oil doesn't have this problem and 5W-30 is always better than 10W-30, at all temperatures. Likewise 0W-30 is always better than 5W-30 and 0W-20 is always better than 5W-20, regardless of what is recommended in your owner's manual and at all temperatures. The only caveat: 0W- oil comes only in synthetic form and you end up spending more money (about $15 more for an oil change) and straining your wallet. Also, obviously, do not use xW-20 if your manual recommends xW-30 or vice versa. But, as explained, it's more than OK to go as low as 0W-xx for 5W-xx or 10W-xx. The digits before the W indicate the cold-engine and "W"inter performance and 0W-xx is always the best for automative engines.

 

In other parts of the world, folks frequently switch among viscosity. Eg: 20W-50 summer, 10W-30 or lighter for winter. I have a 1984 Ford worktruck at my hobby farm, its entire life the motor had 15W-40 summer and 0W-30 winter. It now has 528,000 km on it, motor still pumps up 130 lbs of compression

An oil like Mobil 1 0W-40 meets far stricter specs (ACEA A3/B3 for example) than the other Mobil 1 oils. This oil is specifically designed to meet severe service and extended oil drains - up to 24 months or 30,000 miles - over in Europe

The oil also has far higher TBN and detergent action compared to other oils. It may help dissolve the worst of the sludge and varnish buildup, especially in the crown land and ring land area of the pistons.

I run the 0W-40 in my FJ in summer, and 0W-20 in winter. Excellent used oil analysis results

 

I have been using Pennzoil Platinum synthetic 0W-20 in the heat of Texas, and my 2005 has 86,500 miles and is going strong. I would think the 0w-20 would be perfect for both the colder winters in Maryland, and the hot, very humid summers.

 

Don't be tempted by service categories, certifications, bogus extended-service-interval claims, and European habits. Cars in Europe are driven less and yet break down more often. People there tend to be less conscious about the mechanics of their engine and car.

The most important thing about oil is its viscosity. You don't need 40 weight oil in the spring, fall, or winter. It will do more harm to your engine than good. In the summer use a 40 weight oil only if your engine is running hotter than normal and/or you are doing a lot of high-speed (70+ MPH) or uphill driving, for example if you are living in the desert.

Also, with any kind of engine or type of oil, do not keep the oil in your engine for more than one year or 10,000 to 15,000 miles (whichever comes first) in the worst-case scenario. Contaminants from the blow-by hydrocarbon gases will accumulate in the oil regardless, and there is no way to protect your engine from them other than changing your oil.

 

I see here mentioning 30000 miles service intervals in Europe. There is none like such for cars. Best you can get is 30000 kilometers and not miles, but usually oil quality sensor forces you for an oil change around 22000 kilometers (13700 miles).

Prius in Europe gets 15000 kilometers oil change interval by default (9320 miles), syntetic oil is standard for any Toyota sold in Europe for at last 5 years if not even more.

 

I frequently travel to the EU on business. I see little difference in breakdowns or drivers attitudes towards their vehicles, compared to American drivers

The most important thing about an oil is the additive package. API spec oils purposely ignore protection from things like cold stuck rings, cold black sludge, etc, where ACEA spec oils do demand protection from that

The API spec for oil gellation is so weak that an oil is allowed to have mild gellation. ACEA oils are required to prevent gellation

I've always believed in matching an oil viscosity to ambient temperature. That means 0W-20 or 0W-30 in winter, "whatever" in summer. A conventional 5W-30 oil only has to be "good" or work down to -30 C or -22 F. Colder than that, you're on your own

The fancy additives in premium ACEA oils are designed to protect the motor from all that blowby. You may find this article an interesting read

 

From what I have been told, 30,000 km max for gasoline, 50,000 km max for diesel. The oil quality sensor will tell you when to change the oil

You bring up an interesting question. I have no doubt that Toyota's in the EU are serviced with synthetic ACEA spec oil. Would you happen to know what brand and viscosity oil that would be?

 

I understand one diff between the US and Europe is that the cost of motor oil is much higher in Europe; hence there's an economic incentive to eke out the last bits of life from motor oil there.