How do you know what the MOFT is every second the engine is running in every use condition? You don't really know what "thick as necessary' really is ... except that oil viscosity xW-yy didn't make my engine blow-up. But it could be causing more long term wear. If you could somehow measure the MOFT and correspondinmg wear in every part of the engine (like some controlled engine wear studies do) while putting it through the most stressful use condition you'd use the car in, then you could safely say that a viscosity of xW-yy or higher is giving me adequate wear protection. Obviously some use conditions put more stress on moving parts, and that can make that MOFT go to zero which causes undue wear. Going up a grade, or even two for something like track use is what ensures there is more headroom to keep the MOFT adequate.
If thick oil offers more protection, then isn't cold oil best?
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That's CAFE's tag line based on cars being driven to the grocery store, lol.
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Do I personally know what "thick as necessary" for my engines is? No, the OEM already figured that out, so we don't have to. Why create a boogeyman from nothing?
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See post 42. If people want to run what's speced, then that's all good. But some people understand Tribology and CAFE enough to know that going a bit thicker from xW-20 or lower has some benefit in terms of added wear protection, as pretty much every wear study shows. As mentioned in a few other threads, why did Ford change the viscosity spec for the Coyote in the USA from 5W-20 to 5W-30 and give up some CAFE credits in doing so. If the 5W-20 was going so well in that engine, they wouldn't have bumped it up to 5W-30.
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That's literally a key philosophy within tribology for not just ICE engines but any machinery that requires lubrication, and stems from well before the days of CAFE. Going blindly thick is not an intelligent way to choose a viscosity, as again, thicker viscosity creates more drag on moving parts. More drag is undesirable for obvious reasons.
Hot oil is happy oil. Additives, like most things in chemistry, become more reactive with heat. Different additives, including different variants of the same additive, peak at different temperatures. Oils like HPL Euro and Bad Ass Racing oils don't reach peak friction coefficient until 300-305°F.
Thicker is usually (almost always) better to an extent in terms of wear. There is a point where you can overheat the bearings, resulting in fatigue of the soft metals, due to a combination of decreased oil flow and increased hydrodynamic friction. In some engines, high enough viscosity can break the oil pump shaft. Higher viscosity also tends to increase the pressure drop across the oil filter media which makes it less efficient and more likely to have a failure.
Thicker is usually (almost always) better to an extent in terms of wear. There is a point where you can overheat the bearings, resulting in fatigue of the soft metals, due to a combination of decreased oil flow and increased hydrodynamic friction. In some engines, high enough viscosity can break the oil pump shaft. Higher viscosity also tends to increase the pressure drop across the oil filter media which makes it less efficient and more likely to have a failure.
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For what it's worth, that is nearly zero people on this forum if we're being honest with ourselves.
I'd rather have more drag from more MOFT and then also have better wear protection as a result.
Yes, and why there's a thick vs thin thread born every 3 hours, lol. As much as the basics of Tribology is talked and linked supporting information about it given on this chat board, you'd think more people would understand the basics.
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Can't argue with that.
Agree, hence I use a 30 grade in every vehicle I have that specs 20.
But good luck trying to prove with a t-test that thicker produces statistically better wear results.
Me too. I'd go up a grade on any engine specifying a xW-20 or less. If it specs a xW-30 then I'd probably still go up to a xW-40 for hard track use.
The amount of pressure is key. Again, it’s Boyles law. If you want to argue with physics, I’m the wrong person. There is a variety of valid reason to have oil up to temperature. And utilizing the right viscosity range. But the end argument comes down to volume vs pressure. That’s what was asked in OP’s question.
If you want me to do an exact dissection of your statement. I can another day. But, again. Replying to OP - it comes down to Volume vs Pressure.
Like already said, in a fixed resistance system like an engine oiling system, you get more volume with more pressure. Can't get around that fact of fluid dynamics. Nothing inside an ICE actually depends on the oil pressure between the parts to make the oil lubricate the parts. The oil pressure is only the result of the PD oil pump from forcefully sending oil volume through the oiling system. You could have 150 PSI of pressure in a very flow restrictive system (ie, a badly designed oiling system), but the resulting oil volume going through that system may not be enough to adequately lubricate the parts being force fed the oil. The bottom line is that the engine requires the correct oil volume. The pressure is only the result of getting that volume to the parts. And jornal bearings don't need oil pressure to operate correctly, they just need a minimum supply of oil volume. If that takes 100 PSI or 40 PSI, it doesn't matter if it's still providing an adequate volume to all parts for the operating conditions.
You can't have one without the other in a force fed ICE oiling system. I gotta see this "dissection" of my statement, lol.
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You might want to bone up on physics and fluid dynamics. Boyle's Law pertains to gas, not fluid.
Running a gas in your oiling system really is going "thin". Wonder what the MOFT would be ... parts would be glowing orange and smoking before they locked up.
https://en.wikipedia.org/wiki/Boyle's_law
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I'm extremely sceptical of that story, as the 40 wt, like any other oil thickens significantly when temperature drops and would cause the same issues eventually. In fact there's not likely more than 20°F difference before both oils are the same viscosity. I don't know where he lives, but for me that's the difference between starting during day time or night time....
Now if he put 20W50 in and ran the engine below 0°F, i can see that happening..... but then it would also happen using a 20W-40.
As does higher oil flow. And thinner oil leaks faster from any clearance, needing more volume to compensate.
You might want to bone up on physics and fluid dynamics. Boyle's Law pertains to gas, not fluid.
Running a gas in your oiling system really is going "thin". Wonder what the MOFT would be ... parts would be glowing orange and smoking before they locked up.
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https://en.wikipedia.org/wiki/Boyle's_law
Ok, in your own previous posted, you cited an oil wedge. Is a multi-viscosity oil compressible or not?
At the end of the day, yes. We know oil is compressible. It turns into a solid with enough pressure. Does boyles law exactly translate? No.
Boyles law only translates to ideal gases at moderate temperatures. Then it works pretty well.
However, it still comes down to pressure vs volume. You take a 3in gear pump and a heavy gear oil. Let’s say an EP 220 at 50f. You’re going to have a lot of pressure, and little volume.
Now line up a 36kw pre heater. You’re going to have significantly lower pressure and higher volume. Because the oil is flowing.
The idea, is the same in terms of engineering concepts. Just most people moving remember chemistry 101 over physics 101.
Otherwise, you would have cited me the Hagen–Poiseuille equation. Instead of linking a wiki page of all things. As, that’s what you’re actually looking for.
Before you go google that. I’ll save you the time. It’s not exactly right in situations say, with an engine.
Basically, depending on the constriction, pressure will go up or down. Depending on viscosity. Then you need Bernoulli's principle to figure that out. Which there’s a whole entire formula for that.
With hot oil, the viscosity difference is pretty small, so the difference in dP across the filter (which is pretty free flowing anyway, only around 1/15th the flow resistance of the engine) between a 20, 30 or 40 will be negligible. Better to use an over-sized filter if there is one.
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No, Boyle's Law doesn't apply to liquids. Go read up about it ... you said "If you want to argue with physics, I’m the wrong person." Doesn't see to be the case if your stating the wrong physic law.
Oil is only compressible to a very small degree under very high pressures - see below. The high pressure wedge is created in a journal bearing due to its rotation and can therefore support many thousands of pounds on a small area, like a piston rod after combustion. But that doesn't relate in any way to your claim of "it comes down to Volume vs Pressure". I explained how an oiling system works and the simple relationship between oil pressure and oil volume when fed by a PD oil pump. In and ICE force fed oiling system, pressure and volume are directly related ... can't have one without the other.
Boyle's Law has nothing to do with an engine oiling system, unless you want to try and run air for a "lubricant".
It's really not "pressure vs volume" ... they work hand-in-hand with each other in a predicable manner with respect to an oiling system. What you've said above is basically what I've already said. But the part you don't really seem to understand is that proper lubrication is dependent on supplying an adequate oil volume to the parts. It takes pressure on the oil at the pump to be able to supply that volume throughout the oiling system. The pressure between moving parts due to the oil pressure really doesn't add much if anything to the function of lubrication, including journal bearings. The pressure is just the result of getting a volume of oil through a path of resistance. There were actually old ICEs that simply fed the journal bearings oil simply under the force of gravity - no oil pump at all. @OVERKILL posted up some info on that in another thread discussing lubrication and journal bearings. Maybe he can pop in and share that again here.
I cited the Wikipedia page on Boyle's Law because you didn't really know what "law" it was.
Doesn't matter what "law" you think it behaves as, the fact of fluid dynamics is that on a fixed flow resistance system, you need more pressure to push more volume through the resistance (ie, an engine oiling system) if the viscosity is held constant. And if you held the engine RPM constant to keep the pump output volume constant, the pressure would also go up as the viscosity increased. Every engine oiling system behaves in this basic manner.
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