Clearing up common misconceptions with Oil weights

[Decreppo]

There are two misconceptions out there I can't quite get a straight answer on from searching this and other forums. They are connected so I will keep them to one post.

1)
All over this forum and others I have seen people saying they run a heavier grade oil for the summer months, and a lighter weight oil for winter months. NOT the winter grade number, but the second, oil weight number.

for example, I see people saying that they run Xw-40 in the summer and Xw-20 in the winter. The same can be said for geography. People say they run Xw-40 because they live in Arizona, or that they run Xw-20 because they live in Canada.

Notice how we are ignoring the cold-start/winter weight (0w/5w/10w) for now.

Correct me if I'm wrong but don't all oils run at the same temperature when a car's engine is fully warmed up therefore, no matter where you live, no matter what time of year it is, the second number should stay the same for your oil year round and indiscriminate of location?

2)
the second question I have is in regards to using 10w30 vs 5w30 oils. Lets put aside the debate on whether or not one is better than the other for shear strength or NOACK or whatever etc. etc.

MY question is if you live in a temperate climate, I live in Virginia, is it better for your car to use the 5w in the winter for better cold starts? It got down to 12F here; this is within the range of what a 10w is supposed to be good for. So is the 5w or even a 0w going to reduce engine wear before the engine gets up to temp? What benefit do I gain if the cold start engine temperature is above what 10W is rated for? Is a 0w-40 oil better at 32F than a 10w40 oil?

Would love to hear these cleared up.

 

[Jetronic]

1) No, while coolant temps are fairly tightly regulated, the same isn't true for oil temps. Loads of engines just depend on air passing by the sump for cooling. Though that is changing with modern turbo cars, they are much more likely to have another form of oil cooler aswell. With an easy 100°F swing in ambient air temps in a lot of places between summer and winter, I can definitely see oil temps changing 40°F or more between summer and winter. And an xW-20 running 40°F cooler than an xW-40 is pretty much the same operational viscosity. It all depends how long your typical run is, if there's a benefit or not.

I don't drop viscosity for winter, as i'm wanting the thicker oil to get the engine up to temp sooner, to evaporate water ASAP.

2) It's more complicated than you want to frame it. But if all else is the same, there's no benefit for a 0W-xx at those temps. But not all else is the same, usually.

 

[mark pruett]

Well, @Decreppo, you're opening one of the largest cans of worms on this board.

For point 1:

Some of us feel much the way you do- your engine's cooling system should keep it within the appropriate band for whatever the manufacturer's recommended weight is at operating temperature (the Y in "Xw-Y oil). So if your manufacturer specs 0w-20, there's an understanding that your cooling system and the car's design keep your oil temps in a safe and effective temperature band. It may not be exactly the same as the radiator coolant temp, but close enough.

The other camp, and I may not be very charitable here, goes in for old wives tales, conspiratorial nonsense, and general old fart bullheadedness. They feel like every oil weight change since cars moved away from straight 40 has been environmentally driven (GASP!) government interference, and that they know best about what's going on in their cars because their hobbyist research is just as valid as that of professional engineers at Honda, GM, Ford, Hyundai, etc... They'll try to baffle you with BS about HTHS, film strength, and other technical terms, but when you boil it all down, they're essentially saying that they don't trust the people who made the car, because of conspiracy theories about government emissions controls.

You're not going to get a straight answer.

For point 2: You can't go wrong using what your manufacturer recommendation is. But... you also can't really go too low on the winter side of things either (the first part (Xw) of "Xw-Y"). The reasoning here is that when your engine is cold, even at a mild temp like 70F, your oil is still dramatically thicker than your engine would like. Running a lower winter weight means that it's thinner at colder temps, which means it flows faster, etc... Read AEHaas' description if you want more detail about it.

In the end, run what the manufacturer suggests. Most of the situations where you might need something else are edge cases so rare that the vast majority of vehicles never even come close. Most of us aren't starting our vehicles in N. Dakota without a block heater after a cold front in January. Most of us aren't running them on the track with malfunctioning cooling systems. Most of us aren't hauling huge loads over Towne Pass in Death Valley in July. Most of us are driving them to and from work in normal conditions on normal roads and highways with the occasional minor variation.

 

[kschachn]

MY question is if you live in a temperate climate, Ilive in Virginia, is it better for your car to use the 5w in the winter for better cold starts? It got down to 12F here; this is within the range of what a 10w is supposed to be good for. So is the 5w or even a 0w going to reduce engine wear before the engine gets up to temp? What benefit do I gain if the cold start engine temperature is above what 10W is rated for? Is a 0w-40 oil better at 32F than a 10w40 oil?

The winter rating is one of the most misunderstood topics here and elsewhere. For one thing it isn’t for reducing wear. It’s for pumpability and cranking. This is specific to a temperature. An oil with a 5W rating is guaranteed to pump down to about -30 or so. An oil with a 0W rating is guaranteed to pump below that temperature. How far below is not guaranteed. Above those temperatures there is zero guarantee either one is thinner or thicker.

Pumpability is a binary. Either it will pump or it won’t. If it won’t then all sorts of evil things will happen. If it can be pumped then it will be pumped.

There is no guaranteed benefit to using a 0W oil above -35 or so in terms of either pumping or cranking. However, many oil grades that have a 0W rating achieve that performance through the use of better base stocks. Therefore those oils are generally better overall. So although there is no guaranteed benefit to pumping and cranking, there’s no downside either. It’s not “too thin” at warmer temperatures.

But again it’s not about wear at those temperatures. The greatest amount of wear occurs during warmup and that’s true at much more moderate temperatures.

 

[Texchappy]

the YouTube channel engineering explained had a video* that touched on this.



* not an engineer nor play one on tv so I can’t guarantee the science/accuracy

 

[mojoe]

the YouTube channel engineering explained had a video* that touched on this.



* not an engineer nor play one on tv so I can’t guarantee the science/accuracy

"For most modern engines, wear is not a limiting issue". Meaning you can use lower viscosity oils to take advantage of better efficiency benefits like better fuel economy and more power.

"Can running a thicker engine oil reduce wear?". Yes, but modern engines can use today's thinner oils and maintain reliability.

So, use the lower viscosity oil if that's what is recommended for your car, and quit worrying about it. That seems to be the takeaway.

 

[tcp71]

Well, @Decreppo, you're opening one of the largest cans of worms on this board.

For point 1:

Some of us feel much the way you do- your engine's cooling system should keep it within the appropriate band for whatever the manufacturer's recommended weight is at operating temperature (the Y in "Xw-Y oil). So if your manufacturer specs 0w-20, there's an understanding that your cooling system and the car's design keep your oil temps in a safe and effective temperature band. It may not be exactly the same as the radiator coolant temp, but close enough.

The other camp, and I may not be very charitable here, goes in for old wives tales, conspiratorial nonsense, and general old fart bullheadedness. They feel like every oil weight change since cars moved away from straight 40 has been environmentally driven (GASP!) government interference, and that they know best about what's going on in their cars because their hobbyist research is just as valid as that of professional engineers at Honda, GM, Ford, Hyundai, etc... They'll try to baffle you with BS about HTHS, film strength, and other technical terms, but when you boil it all down, they're essentially saying that they don't trust the people who made the car, because of conspiracy theories about government emissions controls.

You're not going to get a straight answer.

For point 2: You can't go wrong using what your manufacturer recommendation is. But... you also can't really go too low on the winter side of things either (the first part (Xw) of "Xw-Y"). The reasoning here is that when your engine is cold, even at a mild temp like 70F, your oil is still dramatically thicker than your engine would like. Running a lower winter weight means that it's thinner at colder temps, which means it flows faster, etc... Read AEHaas' description if you want more detail about it.

In the end, run what the manufacturer suggests. Most of the situations where you might need something else are edge cases so rare that the vast majority of vehicles never even come close. Most of us aren't starting our vehicles in N. Dakota without a block heater after a cold front in January. Most of us aren't running them on the track with malfunctioning cooling systems. Most of us aren't hauling huge loads over Towne Pass in Death Valley in July. Most of us are driving them to and from work in normal conditions on normal roads and highways with the occasional minor variation.

The engineers who design engines are not the ones making the final decisions. Cost of ownership (sales - less maintenance sells cars), financial implications (accounting - to minimize costs), management decisions and government regulations all play a part in what oil is spec'd.
This sums up an engineer's world:

 

[kschachn]

"For most modern engines, wear is not a limiting issue". Meaning you can use lower viscosity oils to take advantage of better efficiency benefits like better fuel economy and more power.

So, use the lower viscosity oil if that's what is recommended for your car, and quit worrying about it. That seems to be the takeaway.

Yes if you wish. If you don’t then you can use a higher grade without any harm, and is a help with problems such as fuel dilution.

 

[Titan]

What oils use Pour Point Depressants to achieve a lower winter rating...or, is the winter rating now always due to the base oil and other additives in the overall package?

 

[mojoe]

Yes if you wish. If you don’t then you can use a higher grade without any harm, and is a help with problems such as fuel dilution.

How does a higher viscosity help with fuel dilution? Thanks in advance.

 

[Plumb Bob]

How does a higher viscosity help with fuel dilution? Thanks in advance.

Given two different viscosities (The viscosity of a fluid can be defined as the measure of how resistive the fluid is to flow), the higher one will stay so after absorbing the same amount of fuel. Or the ending shake will be thicker, which will help mitigate wear better than the thinner one.

 

[kschachn]

How does a higher viscosity help with fuel dilution? Thanks in advance.

It doesn't help the engine to dilute less, but it helps the oil viscosity from dropping below a grade. Fuel in oil is mostly the dilution of a higher viscosity fluid with one of a lower viscosity which dilutes the oil, reducing the HT/HS. Long-term it can permanently harm the VM in a multigrade oil. So all of which is helped by starting out with a higher grade to help mitigate the loss.

 

[mojoe]

It doesn't help the engine to dilute less, but it helps the oil viscosity from dropping below a grade. Fuel in oil is mostly the dilution of a higher viscosity fluid with one of a lower viscosity which dilutes the oil, reducing the HT/HS. Long-term it can permanently harm the VM in a multigrade oil. So all of which is helped by starting out with a higher grade to help mitigate the loss.

What are HT/HS and VM please?

 

[kschachn]

High temperature high shear and viscosity modifier.

 

[mojoe]

High temperature high shear and viscosity modifier.

Ahhhhh thanks for your patience with a newb. It sounds like using a higher viscosity would definitely be beneficial where fuel dilution was an issue, and as you point out, doing so would not be harmful to your engine. However, it sounds like there is some trade-off with regards to fuel economy and power. I guess the questions are, at what point does potential wear caused by fuel dilution outweigh potential reduction in fuel economy or power, and are any of those factors significant enough to warrant or avoid a change?

 

[kschachn]

Fuel consumption increases about 1% to perhaps 2% for each grade you go up. As for power you'd only really notice that at WOT.

Those factors are significant enough for me, they might not be for you. But there's nothing good about fuel dilution.