Sorry I wasn't clear. I'm using Mobil 1, but in the 10W30 instead of the 5W30. Regarding killing the cats, I've got the hi-flow cats and they were dead before I put them on. Haha, they're the size of a beer can.
Again I apologize for posting too quickly.

 

I have always used Amsoil 0W30 in my C6 with absolutely no problems at all in the Texas heat. In fact, the oil level always stays on the full mark.

 

I run 10W30 Mobile 1 at the suggestion of my tuner. It is largely a function of where I live. My car will likely never see less than 50 deg. F cold start temps.

From what I understand, it takes more additives to achieve the greater differences between the winter and operating temp numbers. Those additives apparently tend to break down more severely than the oil itself under mechanical shear stresses, and can form some nasty residues. So, a narrower range is generally better. Just make sure you select the proper Winter value for where you live. And if you experience extreme temperature swings from summer to winter, a different seasonal blend doesn't seem unreasonable to me at all. Say, 5W30 winter, 10W30 summer. And, of course, this is just for highway use. Track days are a whole notha' story.

FM

 

You could keep everyone happy and run 2 qts each of 0w30, 5w30, and 10w30.

I've seen tons of engine failures over the years and none ever had anything to do with whether it had 5w30 or 10w30 in it. I have a friend that is a fuels and lubes engineer and has done extensive testing of oils. He said the only problem they see related to these two weights is at -20 F, 10w30 will not pass the cold crank RPM test or cold crank pumpability test. Get above 0 F and they both pass all tests just fine.

5w30 will get a hair better fuel econ in the lower temps than 10w30. Ford even went with 5w20 trying to eek out another slight mpg improvement when they got into CAFE problems.

Since 5w30 works perfect in all temps, that's what GM recommends. If you know that the car will never see winter temps below zero, 10w30 will be just fine. That's why a lot of dealers down south use that, a lot of customers want it down there through force of habit and thinking that they need thicker oil in hot weather.

If your down south with no winters, it's really personal opinion on which your brain thinks is the best 0,5, or 10w30. They will all work just fine. Get up north though in the winter and best to use the
0 or 5.

 

There is no special tight tolerances in an LS engine. Looking at the crank and rod bearing clearance specs, they are about the same as any V-8 for decades. LS main bearing clearance specs are .0008 to
.0025". I've been building engines with main bearing clearance in about the middle of that range for decades. About 1 1/2 thou
(.0015") always seems to work good. 2 thou or a hair more on race motors that will get real hot and use thicker oil.

Smaller engines, 4 and 6 bangers use a hair tighter bearing spec due to they don't generate much heat. I rebuilt a V-6 recently, the main bearing spec was .0004 to .0024, and they all landed around .001" when the machine work was done, which seemed to be nicely in the middle.

Anybody that tells you LS engines have some special tight clearances is just passing on rumors. The only real fact is the requirement of synthetic oil, and that is needed because of the high oil temps a vette can see. Little frontal area, tight engine bay, and a performance engine that they know will get driven hard = high oil temps and synthetic oil.

 

5w30 GM knows best!! I don't remember GM saying that 30 year old guys could change their standard or that he takes care of the warranty

 

Keep in mind that GM RECOMMENDS M1 but REQUIRES the 4718 spec. Any oil that meets 4718 will be okay. My personal choice is Amsoil.

 

You guys change your oil? Hmmm...

 

I'ed like to run 10-30 in my motor. But when I do the motor uses a 1qt every 1800-2000 miles. Mine is a forged 427 with .0055 piston to cylinder was clearance using diamond forged pistons. What works best for me is 15-50 mobil 1. It's a little more money about $51.00, but who cares. It's just a little harder to fined sometimes. I called LPE and katech, and they also recommended 15-50 for forged motors. To compensate I let it warm up a little longer before I drive the car. Prior to this motor,
I've had LS type motors since 1999 and always used 10-30 mobil 1 and never had any problems.

 

The new Mobil1 15-50 also has good levels of ZDDP !!!!


DH

 

umm. thats sorta contradicting yourlsef. youre saying that you trust GM's recommendatiopn, but then you use something different??

"Originally Posted by RULEMKR
I believe that GM got it right when the designed the engine and chose the 5w oil to go in it."

 

Took my C6 to WCC to install some side screens.While I was there
decided to have my oil changed.The car has 3400 miles on it.
Upon looking at the receipt I noticed he used mobile 1 synthetic 10w30.
I live near Long Beach,CA.Should I change it out right away or can I
wait for the next 3000 miles.The Tech said it would be ok.

 

With regards to the original question about 10w30 vs 5w30...

10w30 isn't any different than 5w30 at normal operating temp by definition.

A fluid’s viscosity goes down as it heats up. The first number in a multi-grade oil’s rating is its viscosity grade when “cold” (100F), the second its viscosity grade when “hot” (212F). Despite the 2nd number being higher, the oils viscosity is about 5-6 times lower at 212F than it is at 100F.

Both a 10w30 and a 5w30 will have a viscosity in the range of 9.30 - 12.49 cSt at a normal operating temp of 212F.

To determine which oil is "thicker", you really need to take a look at the product data sheets... and then believe them. For example, the product data sheet for Mobil 1 5w30 lists the viscosity as 11.3 at 212F and the product data sheet for their 10w30 lists viscosity as 10.0. Both are in the 30 weight band, but the 5w30 is actually "thicker"... if you believe their data. When cold (100F), Mobil 1 lists the viscosity for the 10w30 as 62 cSt and the viscosity of the 5w30 as 64.8 cSt. This again indicates that their 10w30 actually has a lower viscosity when cold than does their 5w30. Short story, really doesn't look to be much difference at all between the Mobil 1 5w30 and 10w30 and for the original poster and the poster above living in Socal, I'd feel perfectly comfortable leaving the 10w30 in the car unless you are seeing temps below 0F.

As for the comments above on anti-wear additives, the actual additive in question is ZDDP, or Zinc dialkyl dithio phosphate. The new API SM specification limits phosphorus to 0.08% or 800ppm in 30 grade oils, which effectively limits the amount of ZDDP the oil can have.

There were comments above that diesel oils such as Shell Rotella T have higher levels of ZDDP. Unfortunately, the API has made similar restrictions on the newest diesel specification, CJ-4, has they have on API SM automotive oils. According to the new specs for CJ-4, the oil must contain lower levels of ZDDP, Calcium and Phosphorous, it must also not have a TBN any higher than 9. TBN is a measure of the oil’s alkaline reserve, which is used for fighting off the damaging effects of acid. Most diesel oils on the market today are formulated to meet CJ-4 specifications. To look for an oil with higher levels of ZDDP, look for a diesel oil labeled to meet CI-4 or CI-4 Plus and not CJ-4.

For those looking for high ZDDP oils (noting that none of these meet GM Standard 4178M), AMSOIL makes these oils which all have zinc on the order of 1375 ppm, and phosphorus on the order of 1265 ppm.
AMSOIL Series 2000 20w50
AMSOIL SAE Synthetic High Performance 20w50
AMSOIL SAE Synthetic High Performance 10w40
AMSOIL Series 3000 Synthetic 5w30 Heavy Duty Diesel Oil

AMSOIL's best oil which meets GM Standard 4718M is the AMSOIL Signature Series Synthetic 0w30. I run the predecessor of this (the Series 2000 0w30 which I stocked up on) in my 06 CTS-V. Though AMSOIL doesn't come out and say it, it looks like AMSOIL has gone to other anti-wear additives such as Boron and higher levels of Group V basestock (esters) to combat the API SM restrictions on ZDDP in this oil.

 

Thanks for the info Subdriver.

 

BTW, I wish people would learn the difference between "tolerance" and "clearance".

 

I also use Amsoil 0W30. Always stays at the full mark. Best oil on the market today.

 

 

I've been using euro-spec Syntec 0W-30 for awhile (it's SL spec, not SM so supposedly has higher anti-wear additives) - although that's just my choice - I think oil related failures (with any quality oil) are rare - although I know some cam mfrs have commented about SM oils lower anti-wear additives (like Zinc)....

 

tight tolerances? Where do you get the idea that the tolerances are any tighter than the last 40 years of small block or big block motors. Think again. The rods are .0025 and the mains are .0003. As I remember that's the same as the big blocks I built in the 1960's. Any tighter and good by bearings crank rods etc.. Thinner oil means better milage. BTW who's they?
Not an engine builder of any substance. I have a forged LS3/L92 427 and except for the piston to cylinder wall clearence, .0005 vs .0015 the tolerances are the same as a stock LS type motor and I use 15-50
mobil 1. So does LPE and so does katech. And my milage is 25.5mpg. BTW I tried 10-30 worked fine in my LS2 but goes through my present motor at 2000 miles a qt. Went to the 15-50 by recomendation from LPE and don't use any oil at all. My opinion.