Oil Viscosity--Food for Thought or Fuel for a Flame War?

[Captain Dirty]

Observation has shown me that oil clings to vertical surfaces and that time and the inexorable force of gravity causes that coating to thin. Thus I believe that the hardest part of an engine’s life is at start-up before the lubrication system renews the oil coatings.

It seems reasonable that, since modern engines are built to closer tolerances with narrower spaces between parts, thinner, I.e. lower viscosity, oils are desirable to provide lubrication in narrow spaces at low temperatures.

My tractor engine was designed some years ago, and 15W-40 is said to be good for all temperatures. The owner’s manual specifies:

Temperature​	SAE Viscosity​
Above 25°C (77°F)	30​	10W-30​	15W-40​
0 – 25°C	20​	10W 30​	15W-40​
Below 0°C (32°F)	10W​	10W-30​	15W-40​

Lower viscosity winter oils, e.g. 5W had been around for decades.

Now that 0W-40 and 5W-40 oils are available, many on this forum argue that the lower viscosities will lube better at low temperatures, especially at start-up when the engine is cold, and recommend their use.

Could it be that the higher viscosity oils cling more thickly and persistently and thus provide adequate lubrication to the older engines for which they were recommended? Also, might the lower viscosity oils thin too much in the wider spaces?

 

[oosik]

I try not to over think it. My Owners Manual recommends 15W-40 dino oil - that's what I use.

 

[Kioti Dave]

I need to use tractor at temps down to minus 30. I use 0W40 full synthetic. I don't change viscosity in summer. Like oosik, I don't spend much more time thinking about it.

 

[MossRoad]

I, too, follow the manufacturer's recommendations. I can't say that I've ever had a failure that can be traced to the oil. I've had a failure due to lack of oil! But not due to the oil itself.

 

[hube2]

I'm in the "Use what the manual says to use" as well.

 

[Username Taken]

Observation has shown me that oil clings to vertical surfaces and that time and the inexorable force of gravity causes that coating to thin. Thus I believe that the hardest part of an engine’s life is at start-up before the lubrication system renews the oil coatings.

It seems reasonable that, since modern engines are built to closer tolerances with narrower spaces between parts, thinner, I.e. lower viscosity, oils are desirable to provide lubrication in narrow spaces at low temperatures.

My tractor engine was designed some years ago, and 15W-40 is said to be good for all temperatures. The owner’s manual specifies:

Temperature​	SAE Viscosity​
Above 25°C (77°F)	30​	10W-30​	15W-40​
0 – 25°C	20​	10W 30​	15W-40​
Below 0°C (32°F)	10W​	10W-30​	15W-40​

Lower viscosity winter oils, e.g. 5W had been around for decades.

Now that 0W-40 and 5W-40 oils are available, many on this forum argue that the lower viscosities will lube better at low temperatures, especially at start-up when the engine is cold, and recommend their use.

Could it be that the higher viscosity oils cling more thickly and persistently and thus provide adequate lubrication to the older engines for which they were recommended? Also, might the lower viscosity oils thin too much in the wider spaces?

My Cummins came factory-filled with 5w-40 Synthetic. They did that for several years. Don't know what happened, don't care but they're now calling for 10w-30 dino.

I think it's because, when you buy oil by the rail car, the cost can add up. So they're not going to recommend a superior, more expensive oil than what they put in at the Factory. Lawyers would be circling overhead.

So, if a 10w-30 gets them past their initial warranty period, that's really what they're most concerned about.

The perfect oil in a perfectly machined engine would have the viscosity of air but lubricate to 10,000 degrees. No loss of power, no drag on the engine. But that oil doesn't exist and, even if it did, the engine machining technology does not.

If you have a modern engine machined in a modern factory, I'd use a 5w-40 full syn. They'd have to explain to me why they're recommending 10w-30. Like; are the pistons barrel-shaped (for heat expansion)? Is there a lot of 'piston slap' with a lighter weight oil (If so, I'd find another manufacturer)? Are the injectors run by oil pressure? Even then, heavy oil is a waste.

Or is just Luddites that refuse to recognize change?

Giving away my age, here, but I remember the argument about detergent vs non detergent oil. I was also a very smart little kid, too bad it didn't stick. I can also remember the argument over seat belts and why we should use them.

I can also remember when people called radial tires 'radio' tires.

OTOH, I'm not one to latch onto every new fad that rolls around; but I think synthetic oil has been around long enough (80 years?) to know what's what.

Synthetic is superior to dino oil in every way. That doesn't mean that the new dino oils are junk. People take that the wrong way and they shouldn't. Some of it is very good. Some is excellent.

But synthetic is better

 

[mo1]

What grade of oil you use if a range of grades is given in your manual depends on the temperature you intend to use your tractor in as well as how hard you intend to run it.

- If you use your tractor in particularly cold weather, an oil with a lower cold viscosity (e.g. 10W-40 instead of 15W-40) will flow better when cold, leading to better lubrication and easier cranking when it's cold.
- If you run your tractor at sustained high loads in hot weather and not much in the cold, the oil with the highest cold and hot viscosities (e.g. 15W-40 instead of 10W-40) will thin out the least and thus protect the best during this usage. (Look at the 150 C High Temp High Stress results, the lower the viscosity index, the higher the HTHS in general.)
- If you run your tractor in some fairly cold and hot weather and don't change it more than once per year, use an old with a low cold viscosity and a high hot viscosity (e.g. 0W-40, 5W-40).
- If you don't run your tractor at high loads when it's hot, or don't run it in all that hot of weather, choosing an oil with a more moderate hot viscosity (e.g. 10W-30 instead of 10W-40 or 15W-40) will lead to slightly better fuel economy. This is why 10W-30 is being specified in a lot of OTR applications, it's a slight improvement in fuel mileage over 15W-40 and OTR engines run at lower sustained loads than ag tractors.

 

[Cougsfan]

Perhaps if I lived in Antarctica I might consider putting 0-40 to replace the 10-40 recommended by my manufacture. But I don't plan on moving there soon so I will stick with what is recommended. Sometimes you are better off not to try to outsmart the factory engineers.

 

[CalG]

IF

Anyone can cite ONE example of a premature engine failure due solely to use of incorrect oil viscosity, I WILL EAT MY HAT!

It's a non issue. Engines and lubricants are "TOO GOOD"!

Test

Without looking it up "on the interweb"

Explain

10-W40
and 10w-40

An argument for idiots!

 

[4570Man]

IF

Anyone can cite ONE example of a premature engine failure due solely to use of incorrect oil viscosity, I WILL EAT MY HAT!

It's a non issue. Engines and lubricants are "TOO GOOD"!

Test

Without looking it up "on the interweb"

Explain

10-W40
and 10w-40

An argument for idiots!

It’s not uncommon for people working with diesel equipment to dump 15w-40 in their gas pickups and it’s been fairly well documented that Ford 5.4s or v-10s don’t like that.