Engine Oil Viscosity Faq


Use Straight-Weight Oil for the Best Lubrication


> Maybe its time to revisit the paper on motor oil- heres the link
> http://members.nbci.com/minimopar/oil.html
> Have used Valvoline 10w30 for years winter and summer without incident
> for years.....Am begining to use 5w30 .......Straight 30w oil went out of
> favor back in the 60s anyone advocating its use is way behind the
> times......check out that link on motor oil I posted the other day.....
> jim

per the above link: "...This is why single-grade oils are very bad. Straight 30 weight oil is way too thick when cold to properly lubricate the engine."

it appears that blanket statement was made without qualifying the ambient air temps involved, so perhaps the author can be excused for merely his inability to communicate... as opposed to a fundamental ignorance about the properties of engine oil:

"...Multi viscosity oils are one of the great improvements in oils, but they should be chosen wisely... The polymers can shear and burn forming deposits that can cause ring sticking and other problems. 10W-40 and 5W-30 require a lot of polymers (synthetics excluded) to achieve that (viscosity)range. This has caused problems in diesel engines, but fewer polymers are better for all engines. The wide viscosity range oils, in general, are more prone to viscosity and thermal breakdown due to the high polymer content. It is the oil that lubricates, not the additives. Oils that can do their job with the fewest additives are the best." http://www.vtr.org/maintain/oil-overview.html

"...In operation, the viscosity modifiers used in multigrade lubricants for engines, transmissions and gearboxes experience both temporary and permanent viscosity loss." http://www.lubrizol.com/referencelibrary/newsline/1998/decnews.htm

"...Any 5W-30 engine oil, including the synthetic in C5s, uses chemical additives, called "viscosity-index (VI) improvers", to widen its viscosity range enough to make it a 5W-30. VI improvers contribute little to lubrication and can make a "multi-vis" oil less effective at high temperatures than an oil without them. This can become a problem when the oil is under high shear loads at temperatures above 225F. It becomes a potentially damaging problem when oil temp. approaches 300F. If your oil temperature in the pan is 250F or above, bet that oil temp in bearings is approaching 300. Near the piston ring lands and the upper sections of the cylinder walls, it is that or above.

Another characteristic of a 5W-30 that can be a problem in severe service is a relatively high evaporation rate at high temperatures compared to lubricants of more narrow viscosity range. A higher evaporation rate contributes to increased oil consumption and substandard lubrication in areas of high temperature." http://www.saabnet.com/aas/1999.W51/1266386494.260766.html

"The primary source of internal contamination of lubricating oils is from breakdown of the oil additive package and chemical interaction of the components (Franklin Associates, 1985, p. 1-10)." http://www.msue.msu.edu/imp/modwq/53279301.html

"...5W-30 is approved for most late-model four-cylinder, V-6 and V-8 engines on a year-round basis. It is not approved for many turbocharged or diesel applications, some high output V-8s, or applications involving driving at sustained highway speeds or towing in hot weather. It may not be the best choice for older, high mileage engines." http://www.dnd-automotive.com/maintenance/oil-type.htm

not to beat a dead horse, but i have received email from people who don't want to pay extra for multi-grade oil, but are questioning the temp ranges that straight 30 weight oil works at... this info should also alleviate any confusion that jim and his mis-informed website recommendation may have caused regarding factory approval of straight-weight oil:

"...if neither sae 5w-30 nor sae 10w-30 grade oils are available, sae 30 grade may be used at temperatures above 40 degrees f(4 degrees c). do not use sae 10w-40 grade oil or any other grade not recommended."
-1992 buick century owners manual, pages 254-255, in reference to both 2.5 & 3.3 litre engines

also note that the recommended temp range for straight 30 weight oil is listed as approximately 33-78 degrees fahrenheit.
-page 5, section 10, of the 1979 volkswagen type 1 bentley manual.

here are some additional links regarding other aspects of engine oil:

"...The current trend is the "90% of your engine wear happens at startup" advertising ploy. This fact is absolutely true, but as it happens, it's less to to with "grinding engine parts" and more to do with combustion. When the combustion gases burn, they form acids which are highly corrosive when their vapours condense. These acids collect in the upper cylinder areas where their temperature is raised above their dew point. The acids condense and etch the cylinder walls and piston rings. In reality, this accounts for over 85% of engine wear, the other 15% being down to abrasion." http://www.geocities.com/chrislonghurst/engineoil_bible.html

"...Ed Kollin thinks like this for fun and for a living, too. After years as a research chemist mothering over the engine test lab at Exxon, he knows exactly what happens when you circulate lubricating blood of a new formula through the crankcase. Now, as director of R&D for Lubrication Science in Scotch Plains, New Jersey, he creates designer lubes to solve special problems. "...I could design an oil for this application," he says brightly, mentioning that he sometimes does special recipes for people he meets in his neighborhood while walking his dog. But for an off-the-shelf blend, he would choose a "heavy duty" oil intended for diesel trucks. Instead of SJ on the can, look for combinations that begin with C (for compression ignition). CG-4 is the latest, preceded by CF-4, CF-2, CF, etc.

A few blends meet both C and S requirements. While the oil part of these diesel oils has the same lubricating qualities as passenger-car oil, the most common heavy-duty viscosity is 15W-40: more syrupy. But the diesels get bigger doses of the additives; up to 80 percent more ZDDP, and 30 to 50 percent more detergent, dispersant, and corrosion inhibitors." http://www.caranddriver.com/xp/Caranddriver/columns/1999/November/199911_column_patri.xml?&page=1


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