Ok, i have noticed that on lots of cars they say NOT to use 10w-40....?? why not...what is so different about it? I use 10w-30 in the summer, 5w-30 in the spring/fall(short hops, cool weather) and 0w-30 in the winter(short hops, cold). 10w and 5w are GTX or Moble 0 and 0w is Moble1.....kind of keeps the engine clean.

 

I once heard that to make 10-40 oil, they take 20-50, and add a bunch of reducers, so you end up with alot less actual oil.

Been years since I heard that tho, and I never did look into if it was actually true. I just use 20-50 for everything anyway.

 

Its another old wives tale that wont die. My dad was using that stuff during the heyday when it was supposed to be so bad for your engine. Even at 150k miles the car he used it in exclusively still didnt use any oil at all, didnt burn any, and was jsut as clean when it came out as when it went in. Ive never understood the deal with 10-40 being bad myself.

 

With conventional oil--the bigger the split in numbers, the more additives are added to the oil. You end up with less oil and more additives with 10w40. However, they still make it because people buy it and use it without any problems.

 

10w40 has a higher vicosity (it's thicker) than 10w30.
If you have an injected engine, you probably don't want to run the 10w40 because the engine generally starts quicker, allowing less time for oil pressure to build.
IMHO, pick an oil (whatever brand that trips your trigger) and stick with it. Same brand same viscisity.
Oil manufacturers use different blends of additives to reach the SAE specification for thier respective products.
One manufacturers additive formula will allow a certain wear pattern, whereas another manufacturers additives may allow a differnt wear pattern.
Just my .02

 

I thought the first # referred to the thickness?
How does an injected engine start quicker?

 

I thought that said WD-40

 

LOL

 

it's ok, i though it did to

 

Okay, guys, let's go through this one more time...

The number preceding the "W" is the low-temperature viscosity, using a unit of measure called "centistokes". A 10W oil will have a viscosity that falls within a certain range of centistokes, a 5W another range (lower centistoke number) which indicates it is thinner than a 10W (although the ranges overlap, so they could be identical), etc. The testing is defined by ASTM, the range by SAE.

The number without the letter is the "normal" operating temperature viscosity. A 30-weight oil (not to be confused with 30W) will fall into a certain centistoke range, a 40-weight within a higher (thicker) range, etc. Also defined by ASTM and SAE.

"Viscosity index" is another ASTM standardized test that quanifies the difference between cold and hot viscosity. The higher the number, the higher the viscosity index. Similarly, the greater the difference between the two numbers, the higher the viscosity index.

Multi-viscosity oils are typically formulated by taking an oil that meets the XW rating and adding a polymer (plastic) called a viscosity index improver, or VI improver. When the oil gets hot, the VI improver molecule chain expands, and takes up more space between the oil molecules, causing the oil to be "thicker" - and therefore meeting the high temp viscosity requirement. The main problem with these VI improvers is that they are susceptible to shear failure and oxidation, meaning they "break down" and form non-lubricating sludge.

As to 10W-40's specifically: in the early '80's, during the "SF" rating days, the majors got pretty sloppy with their formulations and used a lot of and cheap varieties of these VI improvers. GM in particular suffered a lot of warranty claims in their passenger car diesels when the 10W-40 oil would break down and gum up the roller lifters, which then ate up the cam. So, they said "10W-30 only", and carried it over to their gasoline engines as fuel economy and roller lifters became issues in the later '80's.

Want to hear about 5W oils and pour points?

 

Yes

 

I thaught the same with WD-40 LOL

 

I use 10-40 all the time never seem to have any problems with it. OR no problems that i know about at least. What do you guys recommend on a 350?

 

I would like to revise and extend my remarks:
The way the differences were explained to me was the 10w40 is a thicker oil than the 10w30. If that is incorrect I would like to know.
I guess I should have said idles up quicker than starts quicker, all the injected motors that I have encountered will idle up to a fast idle as soon as you start it then come back down to a curb idle. My service manual says this is to get the catalytic converter up to operating temp.
I appologize if I have made any incorrect statements