Oil Change
Race Director
Joined: Oct 2000
Posts: 14,064
Likes: 1,166
From: N. Alabama
Originally Posted by ljcain
Changed oil and used 10w30 instead of 5w30,any one see a problem with this,started but haven't driven yet,thank's .
Do what I and most every other autocrosser out there do, use the 10-30 grade and enjoy your vette for many thousands of trouble free miles.
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Joined: Aug 2001
Posts: 5,364
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From: King George VA
Originally Posted by southern_son
Good question! Owner's manual will not tell you a little trade secret of the oil companies. The smallest molecular structure of synthetic oil base stocks ( mobil 1 included) is 10 grade. To get the 5 grade, one adds viscosity improvers that do nothing for lubricity. The 5 grade simply helps the engine achieve the CAFE ratings.
With conventional oils, an SAE 10 weight is within the 10 weight catagory when cold and as it heats up, it stays within the 10 weight catagory. Keep in mind that the viscosity of a hot (212F) 10 weight is much lower than the viscosity of a cold (100F) 10 weight. Our engines need a 30 weight when hot. Good synthetics have a naturally high viscosity index, thus as a 10 weight synthetic heats up it doesn't thin out as much and stays in a 30 weight catagory. 10w30 synthetics probably don't need any VIs meaning they are much less susceptible to viscosity shear and thinning low out of grade. A 5w30 will need VIs. When cold, these VIs coil up. At higher temps, they uncoil to help make the oil retain its viscosity as it heats up. As they break down (shear down), you are left with the properties of the base oil, a 5w, when cold, but as it heats up without all the VIs present, it won't retain enough viscosity to be a 30 weight and could for example become a 5w20.
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Race Director
Joined: Oct 2000
Posts: 14,064
Likes: 1,166
From: N. Alabama
Subdriver, I think there might be a correction or two in order here. There is no 'weight' designation for oil...only 'grade'. As far as 10-30 grade, by definition the companies have to use VI's to span the different grade classification from 10-30. There is no 5 grade base.
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Joined: Aug 2001
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From: King George VA
Originally Posted by southern_son
Subdriver, I think there might be a correction or two in order here. There is no 'weight' designation for oil...only 'grade'. As far as 10-30 grade, by definition the companies have to use VI's to span the different grade classification from 10-30. There is no 5 grade base.
Last edited by C66 Racing; Mar 8, 2006 at 07:36 PM.
Le Mans Master
Joined: Sep 2003
Posts: 8,847
Likes: 795
From: Longview Texas
Originally Posted by jimmie jam
very nice information fellas. so, do i still put oil in my engine? 
Unless it starts getting below zero degrees in Texas and Florida, you should be alright.
Last edited by TEXHAWK0; Mar 9, 2006 at 09:54 AM.
Race Director
Joined: Oct 2000
Posts: 14,064
Likes: 1,166
From: N. Alabama
Originally Posted by Subdriver
On the grade vs weight, you are correct and I should have been more specific. But, the SAE added SAE 5W to their grade classification in 1950. And, from what I've read, Group IV or V synthetics have a high natural viscosity index and require less VI than petroleum oils do.
Oh yeah, possibly the reason fewer VI's are needed in syns is because the molecules are uniform in the syn base whereas the dino oils are an average (or median) of the different dino molecule sizes to ascertain a certain grade.
Last edited by SouthernSon; Mar 9, 2006 at 11:50 PM.
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