New Sierra HD with 6.6 gasser ordered, wondering about cSt

B

Baveux

Joined
May 25, 2003
Messages
740
Location
Quebec Canada
IM about to buy a 2025 sierra HD with the 6.6.
This truck will tow close to 8000lbs for about 8000km a years and maybe 3000 km as a grocery getter.

GM spec 5w30 Dexos 1 gen3 and I would like to run a 5w40 but I really do not want to screw up my warranty so I will remain within the GM requirement

X Grok AI told me that Valvoline advance is close to the max for a 30 on the viscosity chart something like 11.9 cst do you have any recommendation for me , I need something readily available in Canada .

Does it really matter to look for cSt and or is it a number I should focus on to protect my new engine if I tow in the heat of texas or in the Pen. and or Virginia mountain ?

Thanks guys
 
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by curiosity , whats missing in this oil to meet dexos 1gen 3 .. i dont feel like gambling since this engine had in the early years of production an history of oil consumption and if this is happenning i really do not want to fight with them ... yes I know im a wuss :-)
 
Fwiw I've stopped using 0w-20 on my 21's 6.2 by the second year and have been running 5w-40 for most of its life and I'm still under powertrain warranty and I haven't bothered to keep receipts. Much quieter at hot idle to where I can hear the gdi pump and it burns far less than before.
 
Baveux said:
IM about to buy a 2025 sierra HD with the 6.6.
This truck will tow close to 8000lbs for about 8000km a years and maybe 3000 km as a grocery getter.

GM spec 5w30 Dexos 1 gen3 and I would like to run a 5w40 but I really do not want to screw up my warranty so I will remain within the GM requirement

X Grok AI told me that Valvoline advance is close to the max for a 30 on the viscosity chart something like 11.9 cst do you have any recommendation for me , I need something readily available in Canada .

Does it really matter to look for CST and or is it a number I should focus on to protect my new engine if I tow in the heat of texas or in the Pen. and or Virginia mountain ?

Thanks guys
Click to expand...
The Euro-spec 30s are sort of like an “SAE 35” in that they are thicker 30s and about halfway to the thinner 40s.

It’s worth mentioning that the grade bands get wider as you go up, so you can end up with a pretty large range that falls within “40 grade.” And keep in mind, all those “grades” are just arbitrary cutoffs.

IN other words, I think the actual KV100 does matter. “Room temperature” might be 64F for some people in winter and up to mid-70s for others in the summer. It matters where you are within that range if you want to be most comfortable.
 
I have a 2024 6.6 gasser I tow 3 different trailers with it. It is just a big LT based engine (L8T) without AFM/DOD or whatever they are calling it now. I just run plain ole Dexos 1 Mobil 1 5W-30. Why wouldn't you under warranty? I see no reason why you would run anything else that isn't Dexos.

I will say this, I have oil catch cans on my Trans Am (LS1) Caprice (L77 think LS2ish) and I have one on the L8T/6.6. The L8T is the only catch can that grabs any oil.

When you get the truck check ALL the fluids my front and rear diffs were low and check all the grease fittings. Some of mine were dry.

Having said all of that I am at 7000 miles on the truck. Did my first oil change at 2000 miles and the second at 6000. I plan on 4000-mile oil changes. 90 percent of that is towing. The Mobil 1 does just fine in there.

What color and trim level did you get?

20231231_162246.webp
 
The problem with 5w30 Dexos, is it’s getting thinner every year as they try and improve fuel economy at the expense of wear.
For that reason in Canada, I’d run Petro-Canada Supreme SHP API SQ 5W40 or equivalent. It has the same exact additive package as the 0w20 and 5w30 Dexos licensed oils.
40C 88.9
100C 14.5
HTHS 3.8
Noack 10.0

Havoline 5w40 API SQ is pretty much the same thing (maybe better), if you can find it.
 
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most any 5w-30 will be fine, Valvoline EP 5w-30 would be a fine choice, or Schaeffers 9000 5w-30.
 
I have a 2021 GMC with the 6.6 gas at 36k miles and over 25k of that towing 6500 lb all over the US. 5k OCIs with Quaker State 5w-30 UD or whatever they call it. Uses no oil. The QS had a lower NOACK back when we got the truck that I was interested in because GDI and intake valve deposits. Have 1year of the extended powertrain warranty may continue with the QS or may go to M1 ESP5w-30.

Second what Mike said above bring it home and check all fluids and zerks in the front suspension. A couple are way easier if you replace them with 90 degree fittings. You’ll find them. The spec on the rear diff fluid is about 1/2” below the fill hole btw. Great truck. 👍🏻
 
Obviously trucks are not for racing, but...
I find it VERY entertaining that an ancient 20+ year old Nissan Titan with half the transmission gears and full liter less displacement spanks the GM 6.6. And the Titan ain't no slouch when it comes to towing either.
 
You’re comparing a 1/2 ton to 3/4 ton truck that has more nanny and emission crap on it. My 78 C10 would wax both of them but again it’s not a good comparison of like models.
 
Too funny. 1 YT video means nothing. The weight difference easily explains the spanking. I had a 2018 Titan and knew before I got a 6000 lb travel trailer home I was trading it. Both ends sprung too soft and the shift programming forced it to run at 3000 rpm on flat ground at 65. Not acceptable for a 400 hp/ 400 lb/ft engine. The 6.6 is 400 hp and 460 lb/ft torque and pulls the same trailer loaded up at 1600 rpm on flat ground. It will never drag race or do 0-60s. I really liked the Titan and if we hadn't got the trailer would still have it. Great light duty truck and easy to do 8 hour days in.
 
The 6.6 gasser with 10 speed was tested by motor trend and went 0-60 in 6.4 seconds with 3.73 gears. Now hook 16,000 lbs up to both and see what happens. Wait the Nissan isn't rated for that.
The Nissan says tuned, headers. I bet also exhaust and gears. At the end of the day it is still a half ton and would struggle with my 1800 lbs tongue weigh trailer.It isn't just about 0 to 60 when towing. Duty cycle is important.
 
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