Tighter tolerance and better MPG with synthetic?

[Boss302fan]

Anyone know about the specs on a 03/04 GM 3.8 from the Monte Carlos/Impala SS's, compared to later engines?

These run from 10W30 to 5W30 and I do know some people that use 5W20...

 

[Zaedock]

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!


There are a few things we need to understand before we even compare clearance numbers. Remember that the use of 20wt oils is nothing new! Look at how cooling technology has improved over the decades: Reverse flow pumps, electric fans with variable speed controls, air ducting.... The ability to run 20wt oils throughout the year (i.e. hot summer) relies greatly on the vehicles ability to maintain a consistant oil temperature. That is so very important! OEM's spend millions of dollars testing these systems. Also as equally important - look how far lubricant technology has improved!

Someone in a previous post mentioned the output of the engine determines the typical weight for that application. I would mostly agree with that determination(with several racing exceptions!). Many of these new higher HP vehicles are specifying increased viscosity oils when compared to their daily driver siblings. While the engine structure remains virtually the same, the OEM's spec an increase in lubricant viscosity for an added measure of safety(my opinion).

Engine tolerances over the years have become smaller due to improved manufacturing and materials. The clearances for your every day driver (except for several purpose built machines) have remained nearly the same, although typically on the lower side (if compared to the older bearings clearances) of the spectrum due to the aforementioned tolerance improvement. I would say that you are both right in this regard. That does not mean that the bearings were specifically "designed" for 20wt oils though.

Here are the main and rod bearing numbers for the F134 in my '59 CJ5:

Main:.0003" - .0029"
Rod: .001" - .0019"

Notice the low end of the main. This engine design had the potential to be tighter than many new designs!
It was also run on oils ranging from 20wt to 50wt, and I'm sure higher, as this engine was also used in industrial applications.

The cooling system however, is as basic as you can get! No fan shroud with a hard mounted blade. Poor cooling!

Overall, a modern engine is made to be efficient (lighter materials, sodium filled valves, VCT, etc) and 20wt oils offer less parasitic loss then 30wt or 40wt oils. I would say the entire package is designed to run a thinner lubricant, not necessarily one aspect as discussed in this post.


Wow, what a rant - Ha ha! BTW - I have rebuilt both stock and performance engines ranging from aluminum OHC four poppers to good ol' Chebby V8's. Jeeps are where it's at though...Phew!


Oh, just to comment on the OP, I have never had a mileage increase simply changing from dino to syn. I would also say that a reduction in tolerance numbers does not correlate to using synthetic oil. It is simply the natural improvement of what we build over time.

Also worth mentioning and to throw you for a loop on bearing design vs oil weight - our old friend Gary Allan (God rest his soul) ran Bruce-Blend 0W10 in his 2.5L Jeep four cylinder with some impressive UOA numbers! Was this engine "designed" for 10 weight?!?! HA! God love him - he was a braver man than I.

 

[Jim Allen]

Originally Posted By: Zaedock


There are a few things we need to understand before we even compare clearance numbers. Remember that the use of 20wt oils is nothing new! Look at how cooling technology has improved over the decades: Reverse flow pumps, electric fans with variable speed controls, air ducting.... The ability to run 20wt oils throughout the year (i.e. hot summer) relies greatly on the vehicles ability to maintain a consistant oil temperature. That is so very important! OEM's spend millions of dollars testing these systems. Also as equally important - look how far lubricant technology has improved!



That's it, In a nutshell!

Boy, I sure do miss Gary Allen.

 

[OceanDoctor]

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!


Exactly, it has nothing to do with tolerances. 'Tolerance' is a word a lot of people throw around to sound all technical and precise. While this is a comforting consumer mindset, there is truly a threshold of 'tightness' before things start to mechanically sieze.

 

[Ken2]

Clearance is the desired gap.
Tolerance is the allowable error.

Much (maybe all) relates to the load per unit area--the force against the bearing vs. the square inches of the bearing. 8000 hp per cylinder diesels use 30 wt crankcase oil, 'cuz they're built to handle that force per area of the bearing.

Many good points made above about the oil, but I think the point about the "slickness" of syn is B.S.

 

[mechtech2]

Today's engines are generally smaller than the large V8s or old.
So many clearances ARE smaller.
As an extreme , consider the ring gap on a ship's huge diesel engine vs. a small motorcycle. And all sorts of other parts/clearances.
It has to be so.
I still have never heard how synthetic oil helps with wear or friction vs. dino.

 

[INTJ]

Originally Posted By: 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...


Yeah, these all are essentially the same modulars. I have an '02 4.6, and oil fill cap is stamped in yellow-5w20.

It ( MC semi-synthetic/5w20) was born out from the Motor company having to engineer an oil to meet new fuel economy standards, at that given time. In my Haynes manual there is a pic of a generic oil cap for a Triton stamped in yellow " Oil."

It is fairly common to have a quarter million miles on the clock with these Tritons, along with very little oil consumption-- and in some cases, none.

For the theme of the thread, I'd would agree on the variances on clearances are tighter, thus tighter tolerances, but generally not the clearances, per say.

Now, I've seen some import advertising specs, saying the clearances are engineered smaller, and the rationale for the required 0w20 oil....Honda comes to mind.

 

[Clevy]

Originally Posted By: INTJ
Originally Posted By: 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...


Yeah, these all are essentially the same modulars. I have an '02 4.6, and oil fill cap is stamped in yellow-5w20.

It ( MC semi-synthetic/5w20) was born out from the Motor company having to
engineer an oil to meet new fuel economy standards, at that given time. In my Haynes manual there is a pic of a generic oil cap for a Triton stamped in yellow " Oil."
It is fairly common to have a quarter million miles on the clock with these Tritons, along with very little oil consumption-- and in some cases, none.

For the theme of the thread, I'd would agree on the variances on clearances are tighter, thus tighter tolerances, but generally not the clearances, per say.

Now, I've seen some import advertising specs, saying the clearances are engineered smaller, and the rationale for the required 0w20 oil....Honda comes to mind.
Ford back-spec'd 5w-20 due to CAFE. That is the only reason. I have a 2000 mustang gt and the 99 cap says 5w-30. Mine says 5w-20. The motors are identcal. Ford used windsors(8 bolt crank) up until 2000. 2001 they were made in Romeo(6 bolt cranks).
I will never put that 5w-20(water) in my motor. Especially since these motors love to rev and there are so many good oils out there with a stronger film strength.

 

[INTJ]

Originally Posted By: mechtech2
Today's engines are generally smaller than the large V8s or old.
So many clearances ARE smaller.
As an extreme , consider the ring gap on a ship's huge diesel engine vs. a small motorcycle. And all sorts of other parts/clearances.
It has to be so.
I still have never heard how synthetic oil helps with wear or friction vs. dino.


The theory of less friction is from the greater uniformity of the synthetic molecules that would buffer the metal to metal contact. The less uniform an oil( dino) has in "size," would translate into a smaller clearance , overall. That is the idea. Now I'd guess to prove this would be a Dyno comparison in HP gains.

One "gain" anecdote here I've experienced is going with a PAO synthetic over Nissan oil. This is from my wife's next generation 4.0 Xterra that
had an increase in fuel economy along with a noticeable release in friction on the motor side. It was like losing 500 #'s.

All subjective, though, and your mileage may vary. For example, my F150 has the same economy as dino, semi-dino, group III, and group IV.

 

[hemitruck]

Originally Posted By: 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.


that and the new metals keep the the spec'd tolerance far longer than engines of the past.

 

[Garak]

Originally Posted By: 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...


It might be interesting to compare some trends with engines that were speced from the start with a 5w-20 or 0w-20, as opposed to something that was backspeced or switched along the way.

 

[FastGame]

Wasn't all this xW-20 stuff the result of CAFE ? CAFE has nothing to do with vehicles being backed specked to xW-20. The auto companies found that xW-20 oils were better and provide all the protection needed in their engines.

Or

The auto companies figured that back specked vehicles wouldn't last as long and they would sell new cars sooner.

 

[mechtech2]

INTJ -
The different sized molecules in the dino may be better for friction, then.

 

[Cujet]

As mentioned above, 20W oils are nothing new. My grandfather had a stash of 20W, his favorite WW-II oil. "Worked in any condition". Since his cars lasted forever, he must have done something right!

My point above about typical automotive crankshaft clearance remains accurate. They typically hover around 0.001 inches in real world builds.

A post above notes 0.0003 as a "tight" clearance tolerance. Wow, that's tight. We tried building turbo Ford race engines with the very best parts and accurate machining to that spec, back in 1979. It was perfectly free prior to startup. Needless to say, it seized right up, instantly. No damage was done to any part, but when it heated up, the clearance went away and the result was lockup.

I still remember that job very well. We carefully polished the crank for 0.001 inches of clearance, re-used the bearings and the result was a very successful engine.

 

[lt2000]

The 3.0 v6 in toyota's have five different sizes of main bearings to select from when building that engine.
gary

 

[Michael_P]

More mass of metal, more expansion and contraction. Just thought I would try to add a new dimension. BTW: I'm saving this thread under favorites. It's a good one.

 

[fpracha]

Originally Posted By: INTJ
Originally Posted By: mechtech2
I still have never heard how synthetic oil helps with wear or friction vs. dino.

One "gain" anecdote here I've experienced is going with a PAO synthetic over Nissan oil. This is from my wife's next generation 4.0 Xterra that
had an increase in fuel economy along with a noticeable release in friction on the motor side. It was like losing 500 #'s.

All subjective, though, and your mileage may vary. For example, my F150 has the same economy as dino, semi-dino, group III, and group IV.
Yes, possible, but were all these oils of same multi-viscosity grade or different?

 

[fpracha]

Originally Posted By: Cujet
My grandfather had a stash of 20W, his favorite WW-II oil. "Worked in any condition". Since his cars lasted forever, he must have done something right!

A post above notes 0.0003 as a "tight" clearance tolerance. Wow, that's tight. We tried building turbo Ford race engines with the very best parts and accurate machining to that spec, back in 1979. It was perfectly free prior to startup. Needless to say, it seized right up, instantly. No damage was done to any part, but when it heated up, the clearance went away and the result was lockup.

I still remember that job very well. We carefully polished the crank for 0.001 inches of clearance, re-used the bearings and the result was a very successful engine.
This just goes to prove that a well-engineered engine would last a lifetime regardless of dino or synthetic oil being used. Clearances and tolerances are a vital part in designing a well-engineered long lasting engine! Proper driving technique so as not to ruin or prematurely wear out the engine is equally important, though!

 

[SteveSRT8]

Actually the duty cycle is being revealed as the arbiter of oil choice.

You can run 20w if you have a light duty cycle, but it's not going to work on that long steep uphill grade when the boost kicks in.

 

[TFB1]

Originally Posted By: Cujet
As mentioned above, 20W oils are nothing new. My grandfather had a stash of 20W, his favorite WW-II oil. "Worked in any condition". Since his cars lasted forever, he must have done something right!
Yeah 20W was fine in in those older vehicles, but most miss the fact that a 160* degree thermostat was used in the summer and 180* in the winter, so few engines were anywhere nearly as hot as today... When engines started using 195F+ thermostats the 30 & 40w oils went into widespread use... No doubt oils today are far better than years back, so a engine that that isn't highly stressed will have a happy life using a 0w/5w-20... The hard working and Hi-Po engines are specked with higher viscosity oils for a good reason...