Why The Dislike For 20W-50?

[userfriendly]

If bearing clearance dictates the HTHS requirement of the oil,
an engine with tight bearing clearances could lose more power to
friction with 0W20 than an engine with lose bearing clearances
would with 20W50.
I read somewhere that oil shear rate and friction increases when bearing clearances decrease.
To improve economy, if the above is true, then engine bearing
clearances should be increased.

The drive for lower HTHS engine oils would not be to satisfy the bearing clearances, as they can be adjusted, but to lower the viscous drag on the cylinder walls.

If HTHS is the true grade of an engine oil, and it seems to be the most talked about specification, then the grading system can be simplified.

I like Shannow's post in the "new HDMO category" thread.

Example; 4.0/5W says it all.
"Operational viscosity" is never discussed except during the warm-up cycle, which may be a moot point.

 

[Shannow]

Too true, it seems counter-intuitive that Honda would narrow bearing clearances, increase diameters and width while going to lower viscosity oils as the dimensional changes increase drag.

But they are trying to balance the whole package.

I think that they are at the limit on the bearing end, but have somewhere to move on cylinders, as you state...now they HAVE to increase bearing dimensions and suffer the drag to go the next overall step.

It won't be long before we see thermal barrier coatings (on the wet side) of cylinder liners to modify the viscosity (downwards) on mid stroke, while leaving it a little thicker at the reversal points.

One of my lecturers back at University stated that we need two (or three) separate lubricants in an engine.

One for the bearings (really only an RandO additive package, pick the operating viscosity)
One for the cylinders (more additised, lower viscosity, higher evaporation resistance)
(One for the valvetrain, highly additised).

The BIG marine diesels have different lubricants for each compartmet.

But we've got a common sump, and have to manage all of the issues with a single compromised lubricant (and mechanical design).

 

[userfriendly]

Its funny you mentioned thermal blocking, because that has been on my mind all day.
I had to use a life-line and phoned my cousin the astro-physics professor about how heat
travels.
After an hour of catatonic stare, I came up with a clear glass oil pan and the
colour of oil matters.
More serious, the crankshaft must be heated from heat passing through the oil.
I'll work on the rest.

 

[Shannow]

Crank will be heated by the friction that's generated "shearing" through the oil.

There's a couple hundred watts per bearing in work taking place against the oil...most of the heat exits with the oil (see my Italian Tuneup thread, where I can get to 130C+ just buy running 4,000RPM for 15 minutes at highway speed).

This will drag the crankshaft metal temperature up.

 

[userfriendly]

Good. That is one engine part we agree on. The crank is heated by the oil and not from
the migration of combustion heat.
Next is the connecting rod which is separated from metal to metal contact from the piston pin and crank journal by a hydrodynamic film of oil.
The connecting rod would also be heated by the friction resulting from the shearing of the engine oil particularly at the big-end.
The shear-rate at the small end of the connecting rod is likely too low to significantly raise the oil temperature.
Combustion heat would have to radiate through a film of oil to get to the connecting rod.
This is where my life-line became necessary.

Heat is a wave-length travelling at the speed of light in open space.
Does the heat actually radiate through the engine oil to warm the connecting rod
or does the oil absorb the heat and release it to the connecting rod?

This is where my thoughts on the colour of oil came from. Could pigment change the
heat transfer rate of an engine oil?
Even if the heat is generated by the friction of the lubricant?

 

[tig1]

Your question should be(Why would anyone use 20-50?).

 

[turtlevette]

Originally Posted By: used_0il
Heat is a wave-length travelling at the speed of light in open space.



Infra Red is but that's not the major mechanism of heat flow in an engine. More like molecules just bumping against each other and its very slow.

I'm going to start running 20w-50 in my Trans Am but only because its hurt and needs some sort of band aid oil.

 

[Shannow]

Originally Posted By: used_0il
Heat is a wave-length travelling at the speed of light in open space.
Does the heat actually radiate through the engine oil to warm the connecting rod or does the oil absorb the heat and release it to the connecting rod?


Temperature is indicative of the excited motion of molecules...e.g. absolute zero is theoretically no movement, hotter they get, more movement.

Heat is the thermal energy that's inherent in an item at a temperature...to increase the thermal energy, you need to have something that's hotter near it to transfer some of it's heat across.

Heat can be moved via radiation (which is what you described), conduction, and convection.

All bodies with a temperature that is above absolute zero radiate heat (proportional to the temperature in Kelvins (same as celsius, but zero is absolute zero)), raised to the power of 4...everything in it's turn absorbs radiant heat....the transfer between them is proportional to Th^4-Tc^4 (h being hot, c being cold)

If you put something hot next to something cold, in intimate contact, the heat will be transferred via conduction.

If you have a moving fluid against something hot (or hot fluid against something cold), it will be convection.

Convection is what really is capable of transferring large amounts of heat around, and is probably what's doing most of the heat transfer in an engine.

Take my L67, as an example...
* the oil draining down the valley is heated to coolant temperature by convection.
* the oil flung to the piston underside will be heated by convection with the hot piston.
* it's cooled in the winged sump by convection, itself with the sump walls, and the sump with air.
* piston ring area...nasty mix of radiation, conduction, convection, comparatively small volumes 10ml(??) compared to the sump, but 250-300C.

Spinning an engine without fuel brings the oil up to nearly full temperature.

 

[killswitch83]

Originally Posted By: Shannow
Too true, it seems counter-intuitive that Honda would narrow bearing clearances, increase diameters and width while going to lower viscosity oils as the dimensional changes increase drag.

But they are trying to balance the whole package.

I think that they are at the limit on the bearing end, but have somewhere to move on cylinders, as you state...now they HAVE to increase bearing dimensions and suffer the drag to go the next overall step.

It won't be long before we see thermal barrier coatings (on the wet side) of cylinder liners to modify the viscosity (downwards) on mid stroke, while leaving it a little thicker at the reversal points.

One of my lecturers back at University stated that we need two (or three) separate lubricants in an engine.

One for the bearings (really only an RandO additive package, pick the operating viscosity)
One for the cylinders (more additised, lower viscosity, higher evaporation resistance)
(One for the valvetrain, highly additised).

The BIG marine diesels have different lubricants for each compartmet.

But we've got a common sump, and have to manage all of the issues with a single compromised lubricant (and mechanical design).




Thermal Barrier Coatings? Speaking my language now, maybe something of a moly/chromium/nickel combo? The TBC the company I work for typically deals with is Zirconia-based, might not be the best option for a combustion chamber though in certain forms lol...You've piqued my curiosity

 

[Shannow]

Happy that I've made you curious

http://dspace.mit.edu/bitstream/handle/1721.1/92191/897209752.pdf?sequence=1

It's still on topic, as 15W40s are "obsolete" to some.

 

[killswitch83]

Thanks for the post Shannow, a great read thus far!

 

[userfriendly]

We have sacrificial anti-wear additives in lubricants.
Is a sacrificial additive in the form of a heat barrier possible?

Back on topic.
I bought 5 liters of 5W20 to blend with 20W50 that I bought on sale
a year ago.
According to my handy ASTM blending chart at the back of the book,
it only takes 25% of 5W20 to water 20W50 down to something useful.

I've graduated to the HTHS thinking and 5.4/20W is not an engine oil
that fits any of my currant modern applications.

Even 15W/4.4 in my diesel pick-up with an automatic transmission is suspect. (15W40)

I'm blending down to HTHS 3.6-3.9 range from now on with a W number that fits the ambient.

 

[Silk]

Originally Posted By: Shannow
Spinning an engine without fuel brings the oil up to nearly full temperature.


So a full roller/ball bearing engine (motorcycle, say Yamaha XS650 which has ball cam bearings) which takes 20-50 and runs about 3psi - is the oil going to get hot from just turning over?

 

[Shannow]

Originally Posted By: used_0il
Even 15W/4.4 in my diesel pick-up with an automatic transmission is suspect. (15W40)

I'm blending down to HTHS 3.6-3.9 range from now on with a W number that fits the ambient.


I was after a 5W 3.7 in the blend in my Nissan, but the 5W30 turned out a bit thicker than I thought (thus the 5W20 at the end)...next OCI is edge 5W30 A3/B4, which should be around 3.6 out of the bottle.

25W 6.4 I picked up recently might go in the Caprice to see the effect on economy.

 

[Shannow]

Originally Posted By: Silk

So a full roller/ball bearing engine (motorcycle, say Yamaha XS650 which has ball cam bearings) which takes 20-50 and runs about 3psi - is the oil going to get hot from just turning over?


Pistons and rings do the same thing, heating the oil, but yes, replacing the hydrodynamic bearings with (what used to be called) "anti friction" bearings will save a few hundred watts of heating in the crankcase.