I don't have enough info. 
Mobil 1 0w-40
Drifting
Joined: Dec 2005
Posts: 1,720
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From: East Hampton CT
I happened to speak to a Mobil 1 engineer last weekend and he was touting the 0w-40 as the optimal solution for almost all motors.
While this is all well and good, why do they still make 10w-30, 5w-30, 15w-50, 0w-20, etc if the 0w-40 will do everything? Years ago you needed the added viscosity for the "liquid bearing" effect that oil provides....now that the synthetics can handle heat and pressure better, I guess its less of an issue. I do know my oil pressure was in the low to mid 20's at hot idle (130k mi on motor) with 10w-30 Mobil 1 and its now high 20's and low 30's with a blend of 15w-50 and 10w-30. I still like ~30psi at hot idle.....so I pick the proper oil mix to get that.
According to oil "experts", the pressure means very little and you should just run the 0w-40 for optimal fuel economy and hp.
While this is all well and good, why do they still make 10w-30, 5w-30, 15w-50, 0w-20, etc if the 0w-40 will do everything? Years ago you needed the added viscosity for the "liquid bearing" effect that oil provides....now that the synthetics can handle heat and pressure better, I guess its less of an issue. I do know my oil pressure was in the low to mid 20's at hot idle (130k mi on motor) with 10w-30 Mobil 1 and its now high 20's and low 30's with a blend of 15w-50 and 10w-30. I still like ~30psi at hot idle.....so I pick the proper oil mix to get that.
According to oil "experts", the pressure means very little and you should just run the 0w-40 for optimal fuel economy and hp.
Thread Starter
Safety Car
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From: No Star Whackers here. Md.
St. Jude Donor '11
Thank you. I guess I'll put it in. I wasn't sure if it would be all right. Mine has 19,000 on it. I figured it might be better because of some 1/4 mile use.
Thread Starter
Safety Car
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From: No Star Whackers here. Md.
St. Jude Donor '11
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Drifting
Joined: Dec 2005
Posts: 1,720
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From: East Hampton CT
Who's to say what GM would have recommended if they did? Of course we can compare to the 2007-8 manuals and see what they recommend a lighter weight.
My concern with the 0W type oils is less of proper lubrication/pressure and more regarding oil consumption. I have the old "non positive twist" style piston rings that have the "flutter" issue at high rpm. I've noticed increased blow by and oil consumption when revved under load to high rpm. Changing my oil from 10w-30 to 15w-50 has significantly reduced the issue. I suspect people with the revised design rings (started in 2001 or 2002 if I recall) would have much fewer issues.
Race Director
Joined: Jul 2007
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From: Texas Hill Country
The only real drawback to really lightweight oil we have experienced is that it has less "cling" to it and if you do not start your car on a regular basis (race cars, garage queens) then you risk more startup wear.
Racer
Joined: Apr 2007
Posts: 402
Likes: 47
From: Los Angeles California
I purchased the 0w30 Advanced Fuel Economy formula Mobil 1 (green cap) from Wal-Mart and I noticed that Wal-Mart also carries the Mobil 1 oil filters which do a much better job than the blue AC Delco oil filters.
The Mobil 1 0w30 is approved for use in the Corvette. It has the GM4718M spec approval on the back of the bottle.
The 0w30 protects just as good as the 5w30, but has better cold starting characteristics and when the engine is cold, it saves you a bit more fuel. It can only help.
0w40 may be a bit too thick for GM engines. Check your owners's manual and it states NEVER to use any oil thicker than a 10w30.
Hope this helps!
The Mobil 1 0w30 is approved for use in the Corvette. It has the GM4718M spec approval on the back of the bottle.
The 0w30 protects just as good as the 5w30, but has better cold starting characteristics and when the engine is cold, it saves you a bit more fuel. It can only help.
0w40 may be a bit too thick for GM engines. Check your owners's manual and it states NEVER to use any oil thicker than a 10w30.
Hope this helps!
We will see what happens.
Thread Starter
Safety Car
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From: No Star Whackers here. Md.
St. Jude Donor '11
OK, I have a few #s. Cold start up, oil pressure jumped to 42psi then settled in at 38. At 70 mph, 44 to 45 psi. Warm idle,31 to 32. Hammered throttle, 62psi. 190* oil temp. 
btw. this is with a mobil 1 filter.
btw. this is with a mobil 1 filter.
Last edited by lightnin; May 9, 2008 at 09:50 PM. Reason: Add content.
Race Director
Joined: Dec 2000
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From: San Diego CA
The Mobil 1 technical guy to whom I spoke uses 0W-40 in his vehicle in Texas. He told me that it is one of the best all-around oils that Mobil makes. I know that back in 01, Porsche was using it as factory fill in ther Boxsters. I think if I lived in Arizona or area with similar climate, this is what I'd use.
Race Director
Joined: Mar 2001
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From: Whippany NJ
CI 6-7-8-9 Veteran
St. Jude Donor '08-'09
NCM Sinkhole Donor
Corvette manual calls for 5w-30 or 10w30. for me, I follow the requirements to avoid trouble, not ask it to come by for dinner and a movie. 
why do owners go completely the other way when the answer is right in front of you?
why do owners go completely the other way when the answer is right in front of you?
Melting Slicks
Joined: Mar 2004
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From: Farmers Branch TX
Cruise-In VI Veteran
St. Jude Donor '09
I guess I dont see the real advantage. Maybe my logic may be flawed, but with a 0w40 oil, you may use slightly less fuel/gain power during warm up, but then your oil is a thicker viscosity when hot, 40 weight instead of 30 weight, which I believe would create more drag, use more fuel/lose power while hot, but I am sure this is so slight it wouldnt be noticed by the driver. I dont know about anyone else, but my engine spends only a few minutes until the oil is up to temp. I thought the original intent on going to the thinner oils such as 5w30, 5w20 was to get the engines up to temp quicker to reduce emissions output and use slightly less fuel than their thicker counterparts. Feel free to correct me if wrong.
Race Director
Joined: Dec 2000
Posts: 19,304
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From: San Diego CA
From what I recall reading here in this section of the forum, Mobil 1 5W-30 oil is closer to a 20W oil at higher temps than say, Castrol European formula 0W-30. 0W-40 offers more protection at high temps, but if you typically do not see oil temps above 230F, 5W-30 is perfectly fine. I have seen 260F during aggressive mountain runs, so it is then that I wish I had the 0W-40 lubricating my engine. Smaller high-performance engines tend to run hotter than larger equivelents, all other things being equal, hence Porsche's decision to run the 0W-40 in its Boxster. Patman has an above-average knowledge of oils and has posted many times about viscosities and how some brands' oils behave differently compared to other brands' of the same viscosity.