Oil - Another "why" question

[CurlyDave]

Yup.

5W-40 would be even better than 5W-30.

This is what I use in almost everything diesel, once the warranty has expired. Until then, I put whatever the manufacturer wants in it. After that 5W-40.

For gasoline engines, Mobil 1 EP. Over the years, the weights available have changed, but I always used the widest range available. Although there the routine is a little different. DW drives a lot for her business. Since 2004 we have gotten her a new Toyota Highlander which she has serviced at the dealer for the first 100K miles. Whatever oil they want. This takes about 4 years and she gets another one at that time. I inherit the old one. when I inherit it, I switch to Mobil 1 EP. I drive a lot less than she does, so one oil change per year that I do myself. When I get the 4 year old Highlander I pass on the older one which will typically have about 150k miles. So far, they are all still going strong. A family friend has the 2004, and while the electric windows have needed maintenance, the powertrain has been flawless. Not too bad for over 200k miles.

The 2000 F 150 still runs, although it is pushing 200k miles and has developed a lifter tick. It has had Mobli 1 all its life. As soon as the EP came out i switched to that.

Good oil is cheap compared to engine repairs. Is cheap oil as good as top price oil? I don't know, and for the price difference, I don't intend to find out.

 

[ch1ch2]

I once had a motorcycle that would not start in the cold weather if I was not using the recommended cold weather oil.
The recommended summer oil was too heavy to allow the starter to spin fast enough in cold weather.

 

[NibbanaFarm]

Not sure about this but I thought it had a lot to do with two things. Shear strength and bearing clearances.

If the load is high enough, the oil molecules will actually break (shear) and become less effective for lubricating. For example a rear end pinion gear will experience higher shear loads than a motor bearing hence 80w-90 gear lube vs 10w-30 motor oil. (There are other differences too of course between gear lube and motor oil. For example motor oil has to deal with combustion byproducts.)

The motor bearings are of the hydrodynamic type and have to be flooded with oil to work properly. They aren't "rubbing" bearings. So the viscosity would depend on the bearing clearances also. And the oil pump has to supply enough oil to the bearings in the first place. So the oil can't be too viscous.

 

[Copperhead]

Well, if a XXw40 is better than a XXw30, my 2000 Detroit Series 60 with 540,000 miles on the factory reman sure doesn't agree. It regularly moves up to 80,000 lb of truck and cargo. Here is the last 4 oil samples from it. The three most recent are 10w30, the last on the list is a 15w40 I used previously.

 

[CurlyDave]

Not sure about this but I thought it had a lot to do with two things. Shear strength and bearing clearances.

If the load is high enough, the oil molecules will actually break (shear) ...

In mechanical engineering (also in rheology and tribology) shear has a different meaning than that.

...So the viscosity would depend on the bearing clearances also...

Viscosity is a property of the fluid composition and of temperature. Bearing clearances do not have any effect on viscosity. Now if you meant to say: "Recommended oil viscosity would depend on the bearing clearances also." I am in agreement.

But, and this is the part where the math gets very complex very quickly, once a viscosity improver is added to a base stock, viscosity can no longer be described with a simple number. A tensor equation is now required, analysis of even modestly complex situations requires a big computer, and our instincts are sometimes wrong.

 

[dragoneggs]

In mechanical engineering (also in rheology and tribology) shear has a different meaning than that.

...So the viscosity would depend on the bearing clearances also...

Viscosity is a property of the fluid composition and of temperature. Bearing clearances do not have any effect on viscosity. Now if you meant to say: "Recommended oil viscosity would depend on the bearing clearances also." I am in agreement.

But, and this is the part where the math gets very complex very quickly, once a viscosity improver is added to a base stock, viscosity can no longer be described with a simple number. A tensor equation is now required, analysis of even modestly complex situations requires a big computer, and our instincts are sometimes wrong.

Your'e killing me! It's Saturday night.

 

[Copperhead]

And most of the time, the VI is what shears, not the oil itself.

 

[NibbanaFarm]

I don't know anything about diesels so I can't comment on them. I thought that they produced higher shear loads. But it's pretty interesting what copperhead says. I was told by a very good mechanic that the engine bearing tolerances were tighter than they used to be due to improved manufacturing and so they needed lower viscosity oil to be able to flood the bearings.

I don't remember any auto manufacturers recommending Xw-40 oil since the 1980s. I didn't do a survey though. But all my modern vehicles, and small engines for that matter, say to use a lower viscosity. My 1993 Ford Windsor 5.8 has a sticker right on the motor that says to use 10w-30 oil. Of the six post 1990 vehicles I've owned, all have required lower viscosity than Xw-40. Spec'd out in the owners manual.

If 5w-40 is better than the other oils, then why don't any auto manufacturers recommend it?

 

[Beltzington]

If 5w-40 is better than the other oils, then why don't any auto manufacturers recommend it?

And down the rabbit hole we go....

This question was why I started this thread, see attached Duramax owners manual guidelines. 15w-40 is the "best" for your vehicle, however for very cold temperatures 5w-40 may be used. Both my tractor and my truck are 2006 and the tractor service guidelines do not even acknowledge 5w-40 oil exists. I have run both 15w-40 Dino and 5w-40 Synth in my truck and there was no significant difference indicated between the oil analysis.

 

[Gary Fowler]

I have read literally hundreds of articles and reviews on oils and still can't seem to get my brain around the logic of using a heavy weight oil for hotter outside air temps. Why would you use 10w-30 for -20F thru 100F and 15w-40 for -10F thru 120F? I understand the lower cold startup winter weight however the operating weight makes no sense to me as the engine operating temp is well over the outside temp once the engine warms up to, let's say, 180F for discussion. If 10w-30 is ok for a warm engine why recommend 15w-40? My guess is it was nothing to do with outside air temperature and more do with them hedging against the quality of chemicals used to modify the viscosity to increase the span between winter and operating weights. SO, based on this assumption my take-away is if you always use a high quality oil "Brand X" than 5w-40 is the best choice for all situations.

Anyone see this differently?

To understand the way outside temps affect an engine is really simple, just take the human body for instance, a marvelous engine in itself, it burns fuel to make heat and energy just like an internal combustion engine. SO take your human engine to the wood pile and start chopping wood when it is 40F and compare your body temp to what it is if chopping wood at 100F. You would see that you could run your human engine much longer at 40F without overheating than you can at 100F. There isn't much difference in our bodies from an engine, both require fuel, air and water for coolant and if you run out of either, your engine stops.