GM recommends 5W-30 dexos1 Gen3 for my new Sierra HD 6.6 gas engine. I won't risk voiding my warranty, but I'm curious to know if the 5W-30 dexos1 Gen 3 maintains its grade or drops to a 5W-20 prematurely.
Does Dexos1 Gen 5W-30 stay in grade, or .....
- Thread starter Baveux
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wemay
Site Donor 2023
No oil is shear resistant.
If you want to stay within Dexos, then Mobil 1 Truck and SUV 5W-30
https://www.canadiantire.ca/en/pdp/...4-73-l-0289445p.html?rq=Mobil+1+truck+and+suv
Most Dexos or API SP/SQ oils probably will “shear” by 1 cSt or so over 5000 miles before they start to gain viscosity back slowly through oxidation. That alone is usually not enough to take them out of grade as they usually start ~1.5 cSt above the minimum viscosity for SAE30. However, even a moderate amount of fuel dilution (>2.0%) in combination with the above characteristics can take them below SAE 30 minimum viscosity. This is fairly common and while not ideal, doesn’t seem to be noticeably harmful to most engines.
Your 6.6 while not turbocharged, is direct injected, so it may end up close to SAE20 viscosity without dropping all the way into it depending on driving conditions. I would do a used oil analysis from oil analyzers to find out, since they will measure the fuel dilution more accurately than some other labs. Then, if you did fall out of grade you could use an oil with a higher starting viscosity and/or one that shears less than most.
Your 6.6 while not turbocharged, is direct injected, so it may end up close to SAE20 viscosity without dropping all the way into it depending on driving conditions. I would do a used oil analysis from oil analyzers to find out, since they will measure the fuel dilution more accurately than some other labs. Then, if you did fall out of grade you could use an oil with a higher starting viscosity and/or one that shears less than most.
Why?,,,there are many other brands that deliver good results, and even better than this particular one including the boutique ones.
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why would it matter if it drops down to a 20 grade?
That's not true. A monograde is shear proof, and a multi-grade with the proper kind of VII is definitely more shear resistant than one with a cheap VM. HPL has discussed this several times.
On the other hand few engines really have a problem with mechanical shear of the VII. People on here often worry about the shear monster when in reality is rarely an issue. Fuel dilution is far more likely to cause a viscosity deviation than shear.
BrendanC
$100 site donor 2024
in my time working on the 6.6’s, i’ve come to figure out they are just like the LS before them, quiet on valvoline and loud on mobil products. if you absolutely positively must keep dexos in it (you don’t) Valvoline Extended protection 5w-30 gets my vote. otherwise the EPennzoil High Mileage is good stuff.
Mobil 1 Truck and SUV were mentioned by Mobil to have some heat related resistance for hard working trucks. I don't see anything wrong with that option. No need to go boutique since OP wants to stay within OEM warranty compliance.
Dexos licensed, as required by the OP. Blended to be optimal for trucks and SUV, as the name implies.
There are many others as you said; I just recommended one.
if it does not matter why not starting at w20 instead of w30 ?
Nevermind.
Yes! The Mobil 1 Truck and SUV was tested as one of the most shear stable in the M1 lineup. Even beat EP in that particular test. It would be near the top of my list if I cared about dexos and wanted an OTS oil.
wemay
Site Donor 2023
Yes. I wasn't considering monographs since dexos1 doesn't don't qualify. I should have stated it as, no dexos1 oil is shear proof but some are better than others.
Yes you are right about that.
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If it shears down to a 20 grade it’ll likely still be protecting your engine. Just because it drops one grade doesn’t mean your engine is now metal to metal contact
I understand that a 20 still provides engine protection, but some W30, if I recall correctly and based on what I've read here before, tends to stay in grade longer than others. That was my question.
Even though a W20 is protecting the engine, is it really the right viscosity for a 6.6 L8T running under heavy loads for hours, days, or even months? Personally, I don't think so, or GM would have chosen that spec to begin with, likely just to save a mere 0.5 drop of fuel per tank.
In conclusion, the truck is fully covered by both the warranty and GMPP. I’m not planning to crawl under the truck like I’ve done all my life with my vehicles. GMC offers two free oil changes, and my dealership provides one, so I’ll take advantage of those three free oil and filter changes. I plan to keep the truck for a maximum of seven years or 62,000 miles. After that, it’s goodbye Charlie—the warranty and GMPP will be over, and I’ll be too old to haul anything big and heavy.
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GM engineers likely took into account the shearing of the oil weight they recommend for their vehicles. Just like they came up with their dexos requirements.I understand that a 20 still provides engine protection, but some W30, if I recall correctly and based on what I've read here before, tends to stay in grade longer than others. That was my question.
Even though a W20 is protecting the engine, is it really the right viscosity for a 6.6 L8T running under heavy loads for hours, days, or even months? Personally, I don't think so, or GM would have chosen that spec to begin with, likely just to save a mere 0.5 drop of fuel per tank.
In conclusion, the truck is fully covered by both the warranty and GMPP. I’m not planning to crawl under the truck like I’ve done all my life with my vehicles. GMC offers two free oil changes, and my dealership provides one, so I’ll take advantage of those three free oil and filter changes. I plan to keep the truck for a maximum of seven years or 62,000 miles. After that, it’s goodbye Charlie—the warranty and GMPP will be over, and I’ll be too old to haul anything big and heavy.
well ok ...
