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I've been referencing this chart from Driven Racing Oils for mine.
I'm running Redline 20w-50 in my car because I got it for half off, but I'm going to switch to Mobil 1 15w-50 or possibly a 40 grade oil since the mains in my LS7 have about 0.0027" clearance. I also have a Katech red LS9 (high volume) pump in my car, I kind of wish I had gone with the blue LS7 pump because I'm betting it's eating up more horsepower than it really needs to.
And I agree with you about Lucas. Pretty much any oil in the appropriate viscosity from Mobil 1, Pennzoil, Valvoline etc would be better I think.
20w-50 is WAY too thick, and cold flow sucks compared to 5w-30 or 0w40. I'm not being a smart ***, but using something not recommended for what you're using it for is like saying you got a Helluva deal on axle grease for your engine. If it were my engine, and I wanted 40wt, I'd go with 0w-40 in your preferred brand. Thats what GM recommends for several V8 engines now......
Last edited by grinder11; Dec 23, 2025 at 11:14 AM.
I'm going to have to disagree with you there. 20w-50 is not too thick for my application, I wasn't using 20w-50 just because I got a deal on it, I was using Redline because I got a deal on it, I was going to run a 50 grade oil regardless of the brand. I might be sacrificing a bit of power using the thicker oil, but I'm certainly not hurting the engine in any way using this grade of oil. I'm not too concerned with GM's recommendations anymore because the only thing that's still from GM on the longblock is the block itself, everything else is aftermarket.
My car no longer has an oil cooler on it, so the oil temperature is usually in the low 200s, I've seen it get as high as 245 when I'm beating on it. According to Driven Racing Oil, with a 0.0027" clearance on the mains for an aluminum block, a 40 or 50 grade oil is best.
I'm not terribly worried about cold oil flow as the car is rarely driven in sub 60 degree weather. And in the video below, 20w-50 showed less wear than 5w-20 on both startup, and after dyno pulls. After digging around in my engine after running 20w-50, I can tell you for certain that it sticks to engine components much better than the thinner oils, which is probably why it showed less wear in this test. It's also worth noting that as the oil temperature went up, the power loss from the thicker oil was dropped to about 5 hp.
You do you, but I’d highly recommend you putting an oil cooler back on it, and going with a 30w oil. .0027 mains and 30w oil are about perfect. You’ll pick up some power and fuel economy by getting rid of the 50w super thick stuff. Oil flow trumps oil thickness all day. Thicker oil does not protect better than thinner oil…that’s a myth. The thinner oil flows quicker and will cool the bearings better than the 50w. Your bearings will thank you later, but seriously, put a cooler back on it and enjoy the benefits.
By cold start, I didn't necessarily mean below any particular temp. Even at 80°, a cold 20w-50 will flow slower than cold 0w-40. Thicker oil also runs hotter than thinner oil. I may be wrong, but I'll bet your leaving at least 5hp on the table running oil that thick. Obviously, it is your choice....
If you guys want oil FACTS, read up on what Lake Speed has to say. Google his stuff and absorb it. He’s a certified Tribology and oil expert. He runs SPEEdiagnostix which is the industry leading oil analysis outlet. He’s responsible for a lot of Gibbs (Driven) oil products and performance as well, on the track. Lots of guys and outlets do simple testing to try and determine outcomes. The simple method never determines factual data that’s lasting…it takes years of research and science backed methods to determine what’s what…and that applies to many areas of life, not simply oil data.
Being a dinosaur from the 1950s, I can remember well when there was no such thing as synthetic oil. When Mobil 1 came out (no, it wasn't the first synthetic, I believe that was Amsoil) it was revolutionary, widely available at any Mobil gas station (and pretty much nowhere else, at first) and, up until around 15 years ago, it cost pretty much the same as it does now. Which was MIGHTY expensive in 1974 $$! Unless you're running NASCAR, or other endurance type road racing, Mobil 1 is probably satisfactory for 95% of we LS owners. Even a so-so synthetic today is probably way ahead of 1970s/1980s conventional oil......
If you guys want oil FACTS, read up on what Lake Speed has to say. Google his stuff and absorb it. He’s a certified Tribology and oil expert. He runs SPEEdiagnostix which is the industry leading oil analysis outlet. He’s responsible for a lot of Gibbs (Driven) oil products and performance as well, on the track. Lots of guys and outlets do simple testing to try and determine outcomes. The simple method never determines factual data that’s lasting…it takes years of research and science backed methods to determine what’s what…and that applies to many areas of life, not simply oil data.
I wholeheartedly agree. Lake Speed Jr's online content is actually what led me to choosing 50 grade oil for my car. The video I posted was from his YouTube channel, and the chart I posted was from Driven Racing, which they published while he was working for them.
If I put an oil cooler back on my car, I would certainly run a 40 grade or maybe a 30 grade. But when my car had the stock oil cooler on it, I would have to rip on it to get the oil above 160 degrees, and it would take 20 minutes of driving. In the spring and fall, it would often only get up to 140 degrees or less on my commute to work. Without the oil cooler on it, it warms up much faster, and the oil temperature usually levels out around 200-215 degrees depending on ambient temps, which is where I want a semi-daily street car to get so it can boil off any moisture in the oil.
Don't take this the wrong way, I do have a lot of respect for you, but I think a the optimal choice for my application is somewhere between a thick 40 grade and a thin 50 grade. I ended up going with a 50 grade because when I take a quick trip to Mexico, it often gets above 220.
I wholeheartedly agree. Lake Speed Jr's online content is actually what led me to choosing 50 grade oil for my car. The video I posted was from his YouTube channel, and the chart I posted was from Driven Racing, which they published while he was working for them.
If I put an oil cooler back on my car, I would certainly run a 40 grade or maybe a 30 grade. But when my car had the stock oil cooler on it, I would have to rip on it to get the oil above 160 degrees, and it would take 20 minutes of driving. In the spring and fall, it would often only get up to 140 degrees or less on my commute to work. Without the oil cooler on it, it warms up much faster, and the oil temperature usually levels out around 200-215 degrees depending on ambient temps, which is where I want a semi-daily street car to get so it can boil off any moisture in the oil.
Don't take this the wrong way, I do have a lot of respect for you, but I think a the optimal choice for my application is somewhere between a thick 40 grade and a thin 50 grade. I ended up going with a 50 grade because when I take a quick trip to Mexico, it often gets above 220.
Is there such a thing as thick grade 40 oil and thin grade 40 oil??? I thought that the first number was for cold flow only, and at 200° a 40 was a 40.....
Is there such a thing as thick grade 40 oil and thin grade 40 oil??? I thought that the first number was for cold flow only, and at 200° a 40 was a 40.....
It depends on how the 40 weight is achieved. A 0W40 might use additives to get the 40 weight while a 10W40 might use a thicker base stock.
But isn't a 40w a 40w? Doesn't the number reflect its viscosity? Or does the number reflect its protection factor? I always thought the first number reflected the resistance to flow at 0°F. I then thought that why would anyone want to run 10w-40 when 0w-40 offered the same viscosity at 200°, but the cold flow was far superior on the 0w oil. Maybe I've always been wrong??
But isn't a 40w a 40w? Doesn't the number reflect its viscosity? Or does the number reflect its protection factor? I always thought the first number reflected the resistance to flow at 0°F. I then thought that why would anyone want to run 10w-40 when 0w-40 offered the same viscosity at 200°, but the cold flow was far superior on the 0w oil. Maybe I've always been wrong??
Not exactly, it's all measured in centistokes at 100C, and there is a range for each grade of oil.
SAE 20 grades are 5.6 - 9.29 cSt
SAE 30 grades are 9.3 - 12.49 cSt
SAE 40 grades are 12.5 - 16.29 cSt
SAE 50 grades are 16.3 - 21.89 cSt
So Mobil 1 0w40 is known for not being very shear stable, so it will commonly shear down into a 30 grade oil after a few thousand miles. That doesn't mean it's bad, it's just something that may be worth considering. I've run that stuff in my Jetta for the last 14 years and 130,000 miles. At 210,000 miles, it barely burns a drop of oil between changes, and the original turbo, which has not had an easy life, seems to be perfectly happy, even at double the amount of boost VW originally programmed it to run at.
If I understand correctly, the closer the "winter" (first number) rating is to the SAE grade, the more shear stable it tends to be. So a 10w40 is typically more shear stable than a 0w40.
I think you're mostly correct about the "winter" rating, but remember more flow doesn't necessarily always mean better protection. In the video I posted above, the 20w50 showed less wear metals from cold cranking than the 5w20 did. But I wouldn't be surprised if the 5w20 would have outperformed the 20w50 if they were conducting the test at below freezing ambient temperatures.
Most of what I know is from being a dork and watching a ton of Lake Speed Jr's videos. I'm not going to claim to be an expert, but I am pretty confident that what I'm saying is pretty accurate. If only Mr. Polyalphaolefin was still active on this forum so he could weigh in.
If I remember from a Lake Speed's video regarding using diesel oil in a gas engine which isn't recommended because of the extra detergent to combat the soot produced in a diesel engine.
Plus the API rated oil for diesels is different than the SP rating for gasoline engines. But everyone can use whatever they want.
API oil rating chart for diesel and gasoline engines: https://www.api.org/products-and-ser...l-c-categories
Not exactly, it's all measured in centistokes at 100C, and there is a range for each grade of oil.
SAE 20 grades are 5.6 - 9.29 cSt
SAE 30 grades are 9.3 - 12.49 cSt
SAE 40 grades are 12.5 - 16.29 cSt
SAE 50 grades are 16.3 - 21.89 cSt
So Mobil 1 0w40 is known for not being very shear stable, so it will commonly shear down into a 30 grade oil after a few thousand miles. That doesn't mean it's bad, it's just something that may be worth considering. I've run that stuff in my Jetta for the last 14 years and 130,000 miles. At 210,000 miles, it barely burns a drop of oil between changes, and the original turbo, which has not had an easy life, seems to be perfectly happy, even at double the amount of boost VW originally programmed it to run at.
If I understand correctly, the closer the "winter" (first number) rating is to the SAE grade, the more shear stable it tends to be. So a 10w40 is typically more shear stable than a 0w40.
I think you're mostly correct about the "winter" rating, but remember more flow doesn't necessarily always mean better protection. In the video I posted above, the 20w50 showed less wear metals from cold cranking than the 5w20 did. But I wouldn't be surprised if the 5w20 would have outperformed the 20w50 if they were conducting the test at below freezing ambient temperatures.
Most of what I know is from being a dork and watching a ton of Lake Speed Jr's videos. I'm not going to claim to be an expert, but I am pretty confident that what I'm saying is pretty accurate. If only Mr. Polyalphaolefin was still active on this forum so he could weigh in.
Bob570, I realize more flow doesn't mean more protection. BUT-SLOW, OR NO FLOW definitely means not much, or no protection!! I was mainly referring to the longer the bearings go, waiting for thick oil to arrive during the first start of the day, in 45° weather, the more wear they would experience. As for 5w-20 oil, I'd NEVER consider it in my LS7. GM is finding out the hard way that their V8s don't play well with 20wt oil.....
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