Tighter tolerance and better MPG with synthetic?

[sir1900]

This thread is in reference to this discussion over at Club Lexus.

It is a question in reference to switching from dino to synthetic. As you may know, 2011 RX 350s require 0W20, but 5W20 is permitted however the next OCI must be 0W20. 2010 RX350s, with the exact same engine, requires 5W20. One of the quotes in that thread over at CL caught my eye and it states:

Quote:
Yes you can and should go back to full synthetic oil. Toyata and many others have found that the full synthetic oil has a better slickness (for lack of a better word) than dead dino's. This is a big factor in making tolerances tighter and getting better milage.

If you have a Hybrid it states you MUST use full synthetic as they want some lubrication to remain in the motor for the frequent start and stop of the ICE.


In regards to the issue of tolerance (as highlighted in red), my question is: really? The Lexus 3.5 V6 is nothing "special" that requires a fully synthetic oil is it? If anything, the 0W is more for squeezing out an extra MPG or two than engine tolerance is it not?

 

[ahoier]

Perhaps off-topic...but kind of ironic these "Hybrids" - which typically are designed as either flex-fuel, or with "battery packs" to conserve gas; i.e. turn off the engine at low RPMs.....are "requiring" expensive expensive synthetics.....when theoretically, the engine(s) are being ran "less" than a typical engine.....since they go into their battery-run mode, where you can barely even hear the engine running, etc....

I'm a fan of synthetics, but it's just kind of funny, when you think about the rationale.....


I guess that could be perhaps why a lot of them are now supporting 8-12k OCIs, oil life monitors, etc...

 

[demarpaint]

I could see where a hybrid engine would benefit from a 0W20 oil simply because the engine has a lot of on off cycles, and reaching operating temps and staying at operation temps is something that might not happen often. So better cold flow with the 0W20 would help that engine.

 

[Maritime Storm]

So as tolerances the oil should have absolutely no effect on mechanical tolerances between parts. Most 2011 and newer Toyotas call for 0W20 only.

 

[Cujet]

A fairly recent review of internal engine bearing clearance specifications reveals little difference between modern engines that "require" 5W-or-0W-20, when compared to engines made 50 years ago. Crankshaft main and connecting rod bearing clearances hover around 0.001 inches, with less resulting in possible contact and seizure problems and more resulting in oil film issues. With 0.0015 being an common maximum for typical automotive engines.

 

[TFB1]

I regularly see this tighter tolerance B-S spewed over the net...

Tolerance is the variation in size between moving parts, clearance is the actual measurement... A bearing may have a optimal clearance of .0015 but is acceptable anywhere between .001 & .002, that one thousandths difference is the tolerance... A tighter tolerance would mean the clearance is held closer to optimal specs, say .0012 to .0017 or in other words not allowed as much variance... So tighter tolerance means the engine is more closely built to optimum, not that CLEARANCES are less...

 

[SteveSRT8]

As a family with a 3rd generation machinist in it we also agree.

It would seem that clearances are not really changing, perhaps they are simply being held to a closer tolerance with advanced machining processes and quality control.

 

[tig1]

Originally Posted By: Cujet
A fairly recent review of internal engine bearing clearance specifications reveals little difference between modern engines that "require" 5W-or-0W-20, when compared to engines made 50 years ago. Crankshaft main and connecting rod bearing clearances hover around 0.001 inches, with less resulting in possible contact and seizure problems and more resulting in oil film issues. With 0.0015 being an common maximum for typical automotive engines.


Not so. For example for my 2.3 and 2.0 Ford Duratech engine.

Main bearing clearance is .0007-.0013

Intake valve stem to guide clearance .0001

Exhaust valve to stem guide clearance .00011

This is just an example of the tighter clearances in modern Ford engine, and no doubt the same in other engines as well.

 

[SteveSRT8]

I'm sorry, but tighter than what?

Older Fords?

 

[tig1]

Originally Posted By: SteveSRT8
I'm sorry, but tighter than what?

Older Fords?


Tighter than most all older engines. Todays engines are much closer in clearances than yesterdays engines. This is one major reason for oils in the 20 wt range.

 

[SteveSRT8]

You may choose to believe that, but I have seen nothing to indicate that any manufacturer has modified ANY internal engine clearances specifically to use 20 weight oils. The only thing I see them doing is cleaning up their quality control to assure tighter tolerances.

When you look across platforms that use the same engines you see different oils spec'd based on intended use and even which country they ship to.

 

[tig1]

Originally Posted By: SteveSRT8
You may choose to believe that, but I have seen nothing to indicate that any manufacturer has modified ANY internal engine clearances specifically to use 20 weight oils. The only thing I see them doing is cleaning up their quality control to assure tighter tolerances.

When you look across platforms that use the same engines you see different oils spec'd based on intended use and even which country they ship to.


You have it just backwards. Actually the engine tolerances are closer for better performing engines(longer life, more effeciant, higher horsepower). So the engine builders are going to 20wt oils to meet those needs.

 

[partspro]

Clearance, the distance between parts (a gap). Tolerance the variation in said clearance which is allowable (usually +/- something).

Many high performance engines have in fact greater not lesser clearances. The tolerance is usually tighter (blue printed engine).

That being said, I have customers who measure mileage down to the yard and make specific claims of one brand over another using the same weight oils.

 

[tig1]

Originally Posted By: tig1
Originally Posted By: Cujet
A fairly recent review of internal engine bearing clearance specifications reveals little difference between modern engines that "require" 5W-or-0W-20, when compared to engines made 50 years ago. Crankshaft main and connecting rod bearing clearances hover around 0.001 inches, with less resulting in possible contact and seizure problems and more resulting in oil film issues. With 0.0015 being an common maximum for typical automotive engines.


Not so. For example for my 2.3 and 2.0 Ford Duratech engine.

Main bearing clearance is .0007-.0013

Intake valve stem to guide clearance .0001

Exhaust valve to stem guide clearance .00011

This is just an example of the tighter clearances in modern Ford engine, and no doubt the same in other engines as well.


Kinda like these?

 

[SteveSRT8]

sorry, but the numbers posted do not change anything. You'll need some more info to convince me.

Plus, it's actually YOU that has it backwards. Tolerances are the allowable variation, NOT clearances.

Try again!

 

[Jim Allen]

In order to make a useful comparison, we need to find and engine that was pre 20 grade and then made the transition to 20 grade and compare the clearance specs earlier and later.

Also, find a typical older engine and a typical newer one to compare clearances. I think the farther you go back in time, the larger the clearances were in general. Machining tolerances and standards have improved greatly so engines are tighter now because they CAN be tighter and an engine lasts longer with tighter clearances and lower tolerances. In spot checking, I think clearances have tightened up some in some areas but it doesn't appear to me it was done JUST so the engine can run 20 grade oil. If you look at the engines that made the transition, you don't see much difference in the pre 20 grade and post 20 grade engines. It's possible and likely that when they can, they have tighten clearances up... and 20 grade oil has perhaps helped make that possible... but in order to get the oil in there for lubrication, you have to have some clearance.

Many race engines are built with very loose clearances to relieve them of frictional power losses, but they don't automatically run a heavier oil, they just push more oil into the gap. They MIGHT run a heavier oil in some circumstances (high heat and viscosity loss due to it and fuel dilution) but generally they go as light as they can (the engine just has to last for the race... it will get an overhaul after ).

I think it's a mistake to argue this in terms of absolutes. I think a study will show a lot of variation.

 

[demarpaint]

Originally Posted By: Jim Allen
In order to make a useful comparison, we need to find and engine that was pre 20 grade and then made the transition to 20 grade and compare the clearance specs earlier and later.

Also, find a typical older engine and a typical newer one to compare clearances. I think the farther you go back in time, the larger the clearances were in general. Machining tolerances and standards have improved greatly so engines are tighter now because they CAN be tighter and an engine lasts longer with tighter clearances and lower tolerances. In spot checking, I think clearances have tightened up some in some areas but it doesn't appear to me it was done JUST so the engine can run 20 grade oil. If you look at the engines that made the transition, you don't see much difference in the pre 20 grade and post 20 grade engines. It's possible and likely that when they can, they have tighten clearances up... and 20 grade oil has perhaps helped make that possible... but in order to get the oil in there for lubrication, you have to have some clearance.

Many race engines are built with very loose clearances to relieve them of frictional power losses, but they don't automatically run a heavier oil, they just push more oil into the gap. They MIGHT run a heavier oil in some circumstances (high heat and viscosity loss due to it and fuel dilution) but generally they go as light as they can (the engine just has to last for the race... it will get an overhaul after ).

I think it's a mistake to argue this in terms of absolutes. I think a study will show a lot of variation.


Well said, no one can argue the fact that the machines used today in the engine mfg. process is better than the machines used in the past. Better QC, engine design is better too. Show me a stock 3.6L engine from the 1960's-1980's that can push 300HP.

 

[SteveSRT8]

Absolutely!

As an example of oil related madness, look at Chryslers new gen Hemi.

The 5.7 calls for 20w. The trucks call for 30w. The SRT versions call for 40w and 50w!

The basic CLEARANCES in all these engines are the same!

 

[Boss302fan]

Originally Posted By: SteveSRT8
Absolutely!

As an example of oil related madness, look at Chryslers new gen Hemi.

The 5.7 calls for 20w. The trucks call for 30w. The SRT versions call for 40w and 50w!

The basic CLEARANCES in all these engines are the same!


I do know two of the top rebuilders of classic/muscle car engines and they say that clearances are different depending on how you set up the engine. Its what they think is the best clearances for a particular engine and use.

I guess you could use any weight that you want. Depends on what use you have for the vehicle. Racing, towing, highway use, city driving, etc...

 

[TFB1]

Some time back, I did compare the clearances for the '98(5W-30) & '02(5W-20) Ford 2v 4.6L and found no differences in those engines... Would make sense as the earlier engines were backed specked for the lighter oil, still doesn't mean I'm putting the stuff in my crankcase...