Rod and Main bearing clearance

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Originally Posted by tig1
Originally Posted by demarpaint
Originally Posted by JLTD
Originally Posted by OVERKILL


Engineers don't write owners manuals, can you imagine the disaster they would be if they did?
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However, if Engineering input was freely allowed into what you received you would still see a range of viscosities recommending what's ideal for the anticipated operating conditions, which we used to see, and is still seen in some instances abroad. Due to CAFE, this is not possible, the oil that the CAFE qualification was run on must be the spec lubricant IIRC.

Subsequently, we've witnessed the introduction of thermal castration mechanisms that limit specific output if oil temperature gets too high. We've seen more widely the use of heat exchangers to control oil temperature and we've seen the mechanical design changes I've noted to the engines themselves to ensure that they'll survive properly on thinner lubricants.

None of that means that an engine is going to die prematurely on 0w-20 or 5w-20. It may mean slightly better wear performance if one were to do a tear down while running an xW-30 or xW-40, but that may be of zero consequence over the useful life of the equipment. We've had this discussion before. The other side of "better than" is not a pile of failed engines. We are talking what is likely a marginal improvement over what is already acceptable. It has to be acceptable, because it's what is spec'd for the expected lifetime of the equipment. And these improvements are likely only in certain areas.

Also, there is the drive for and expectation of universal lubricants which is why 0w-40 has become so popular for performance applications. The aforementioned lubricant chart can be greatly decreased in complexity due to the availability of these broad spread oils. Ergo, the Corvette has spec'd 5w-30 and 15w-50 and now 0w-40, Ford got away with just spec'ing 5w-50 but could have done a 5w-20/5w-50 recommendation. FCA went with 0w-40. The 5.7L HEMI has also simultaneously spec'd 5w-20 and 5w-30 depending on application. Without CAFE the former would have perhaps spec'd both.

We still see some of this verbiage hinted at in some manuals where there is a remark that a heavier lubricant may be preferable when towing for example or something similar. But it's not a requirement; it can't be for an application for which CAFE credits are claimed. Without that requirement you'd likely see less ambiguous language.


Overkill, thanks for summing up all the arguments about CAFE and thick vs thin in once concise and intelligent post! You've said here what I've been trying to say for some time....

This is just one of many reasons why I dropped the 20 grade oil for 30 in both my Jeeps. There are many people that are experts I was fortunate enough to speak with which made the decision quite easy for me.

And I went from a 5-30 to 0-20 on the advise of several posters here that have done the same with engines clocking 300K and beyond. With aprox 475K using 20- wt. in my last 3 engines, all is well.

Fantastic!
 
4WD, duly noted...
The OEMs, per their papers are trying to maintain crankshaft alignment at all costs, which makes sense in a regime of lower MOFTs.

Racers, on those machined bottom small blocks, and the various families of sixes would open up the clearances some, to paraphrase Smokey, to let the bottom end do it's hoochiecooch thing.
 
Originally Posted by StevieC
My point is we shouldn't be playing engineer here. If the engineer calls for a 20wt, use a 20wt. If they call for a 30wt use a 30wt. But blanket statements here of using 30 or 40 weights in applications that call for 20wts because it will somehow offer better protection because of international manuals allowing for 30wts to be used is just ridiculous.

Tig's experiences along with others here using what the manufacturer calls for proves that.

That said I will report back when I get to 1/2 a million kilometers again in the PentaStar which shouldn't take too long considering I have gotten to 14K already. But I'm sure that will be explained away with "Yeah but those are highway miles"
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or some other excuse followed by and if you think it was Amsoil that gave your those miles any shelf oil would have done the same as I'm sure will be the case if I'm lucky enough to get to 1,000,000km or 1.6M KM.
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It's hilarious because over a decade ago it was the 20w50 crowd against the 30wt crowd, now it's the 30wt / 0w40 crowd over the 20wt folks.




Well ... woke up this morning finding a mistake made by one of my engineers - And Ford has changed up a grade post sales and some miles on units (ever accuse GM of using customers to test vehicles) and we all know several engines run in the US on thinner oil will use a grade up in Oz or the EU ...
So another endless debate between 20's and 30's will get nowhere ... I'm running 20's in three in signature - and the one that was spec'd a 30 gets 30 or 40 ... and anyone of them can run fine with 5w30 ... Anyone doubt that ?
 
Originally Posted by Shannow
4WD, duly noted...
The OEMs, per their papers are trying to maintain crankshaft alignment at all costs, which makes sense in a regime of lower MOFTs.

Racers, on those machined bottom small blocks, and the various families of sixes would open up the clearances some, to paraphrase Smokey, to let the bottom end do it's hoochiecooch thing.


Copy that ... my auto mechanics teacher in HS worked over his B/BP/ported SBC (with some helpers - I was a port flapper, LoL) like that and put that motor in an early 60's Ford Falcon (same car my dad had the I6 in) ...
The picture you posted reminded me of his car ... it would barely lift one tire and the car flexed so much that other tire was never coming off the ground ...
That car had the rumpity, rumpity, sound to where nobody got suckered into a sleeper race ...
 
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