Another oil weight question

[Marky Dissod]

... DFM / ASS being disabled ...

You disabled your ASS.

 

[Vector]

is there any truth to this? documented? i never put any thought to that.

Without going into detail (you can go down the rabbit hole if you wish), yes CAFE standards caused GM and others in the USA to use colored water instead of quality protective oil, ATF, etc.
All to meet certain MPG criteria, environmental rubbish, the customer be damned.

 

[sohanrd]

Yes, nothing to do with feelings, everything to do with how motor oil works.
GM OE recommended motor oil for 6.6l L8T is Dexos 5w30. Outside of the continental US, GM OE recommended motor oil is usually 5w30.
So, yes, 5w30.

Interesting.

I was checking the Tahoe manual for UAE and the only option given there is 0w-20.

From what I understand only countries they recommend 5w-30 is the versions with no DFM engines like in Australia/South America, etc..All the countries with DFM in the V8 still ask for 0w-20

I might be wrong, but it is great if someone more knowledgeable than me can shed their lights on here

 

[jfoj]

I know people running 5W30 and 0W40 without issues. The issue is change it often because the DFM effectively needs hydraulic oil to operate.b

 

[Marky Dissod]

I know people running 5W30 and 0W40 without issues. The issue is change it often, because the DFM effectively needs hydraulic oil to operate.

Lack the credentials to substantiate that 1) the above is true, 2) the primary motive for 0W20 (and lower) is CAFE MpG test scoring ...
but tens of thousands of owners use 5w30 without issue, provided they change oil more often / sooner than recommended by the Oil Life Monitor.

Would you give up 1 or MpG to extend your engine's durability / longevity? Would you change your oil more often?

 

[sohanrd]

Lack the credentials to substantiate that 1) the above is true, 2) the primary motive for 0W20 (and lower) is CAFE MpG test scoring ...
but tens of thousands of owners use 5w30 without issue, provided they change oil more often / sooner than recommended by the Oil Life Monitor.

Would you give up 1 or MpG to extend your engine's durability / longevity? Would you change your oil more often?

Im sure there are tens of thousands of owners use 0w20 without issues as well with proper maintenance.

My question is that if 0w20 is strictly for MPG and CAFE, why do they call for 0w20 in UAE where there is no CAFE applicable for their DFM V8?

 

[Vladimir2306]

Im sure there are tens of thousands of owners use 0w20 without issues as well with proper maintenance.

My question is that if 0w20 is strictly for MPG and CAFE, why do they call for 0w20 in UAE where there is no CAFE applicable for their DFM V8?

You're asking the right question, we don't have a CAFE in Russia, but there's also 0-20 oil on GM cars.

 

[sohanrd]

You're asking the right question, we don't have a CAFE in Russia, but there's also 0-20 oil on GM cars.

Those GM V8s in there DFM or no?

 

[Vladimir2306]

Those GM V8s in there DFM or no?

Yes, of course, with DFM

 

[sohanrd]

Yes, of course, with DFM

Exactly, 0W‑20 has more to do with the DFM system than with CAFE imo. DFM needs quick oil‑pressure changes to operate correctly, even at low temperatures.

Thicker oil may provide better protection for bearings and other components, but it adds extra risk to the DFM system.

Thats why GM calls for 0W‑20 for all DFM engines in every country (whether they havet CAFE or not), and 5W‑30 for non‑DFM V8s in certain markets. People usually dont check this. They say the same motors use 5w-30 in other countries, which is not simple as it seems.

I dont think any of those YT/forum gurus have ever scientifically tested the effect of higher viscosity oils on DFM. Most of them just say, "I’ve used it for this many years and have this many miles,” Thats all.

Using 5W‑30 may not destroy lifters immediately. But DFM heavily depends on fast oil flow. Dirty oil, cold mornings, slow oil flow, higher viscosity can catalyze those issues when the right combination hits.

That said, using 5W‑30 on a DFM deactivated (via OBD) engine could be beneficial. But I dont know, I could be wrong.

my 2c.

 

[Marky Dissod]

What if you just run your 8L90E in M7 / 10L80E in M9 to avoid final gear and disable Cylinder Confusion that way?
Would using a 5w30 that GM specs for the 6.6L L8T damage the DFM lifters if they never get to DFM?

 

[BacDoc]

Exactly, 0W‑20 has more to do with the DFM system than with CAFE imo. DFM needs quick oil‑pressure changes to operate correctly, even at low temperatures.

Thicker oil may provide better protection for bearings and other components, but it adds extra risk to the DFM system.

Thats why GM calls for 0W‑20 for all DFM engines in every country (whether they havet CAFE or not), and 5W‑30 for non‑DFM V8s in certain markets. People usually dont check this. They say the same motors use 5w-30 in other countries, which is not simple as it seems.

I dont think any of those YT/forum gurus have ever scientifically tested the effect of higher viscosity oils on DFM. Most of them just say, "I’ve used it for this many years and have this many miles,” Thats all.

Using 5W‑30 may not destroy lifters immediately. But DFM heavily depends on fast oil flow. Dirty oil, cold mornings, slow oil flow, higher viscosity can catalyze those issues when the right combination hits.

That said, using 5W‑30 on a DFM deactivated (via OBD) engine could be beneficial. But I dont know, I could be wrong.

my 2c.

This sounds logical but is not correct!

My 2024 Tahoe 6.2l “passed” the pico test and it has DFM.
According to all of GM service bulletins the correct oil for any DFM engine that passes the pico test is 0-40W and definitely not 0-20W for the original and the extended warranty for the recall on the 6.2.
This is straight from GM and not opinion or optional.

 

[sohanrd]

This sounds logical but is not correct!

My 2024 Tahoe 6.2l “passed” the pico test and it has DFM.
According to all of GM service bulletins the correct oil for any DFM engine that passes the pico test is 0-40W and definitely not 0-20W for the original and the extended warranty for the recall on the 6.2.
This is straight from GM and not opinion or optional.

I don’t think this makes the logic incorrect.

0W‑40 still gives you similar viscosity to 0W‑20 at low temperatures, which is exactly where DFM is most vulnerable.

And even if 0W‑40 adds some additional risk to DFM operation, GM will happily accept that future risk in order to avoid the current problem IMO.

 

[sohanrd]

What if you just run your 8L90E in M7 / 10L80E in M9 to avoid final gear and disable Cylinder Confusion that way?
Would using a 5w30 that GM specs for the 6.6L L8T damage the DFM lifters if they never get to DFM?

The L8T is a different engine. It may not have the same DFM plumbing as the L84/L87. An engine can work perfectly with 5W‑30 if its DFM‑related oil passages are designed to handle the higher viscosity without any risk under vulnerable conditions. But we dont know (atleast I dont know) whether the L84/L87(an engine designed around 0W‑20) can safely handle 5W‑30 in every situation without any risk.

Using L9 or a DFM disabler theoretically may remove the lifter's dependency on precise oil‑flow timing, which reduces the risk of failure. But any lifter ,DFM or not, still has its own inherent failure points, and those risks still there.

 

[Jay P Wy]

The L8T doesn't have DFM. As for the low temp oil viscosity, DFM (and AFM before it) is not active when the engine is cold. It's active when engine temp is above 165.

 

[jerry455]

There is no danger to the DFM using other oils besides 0W20. GM has us who passed the PICO test using 0W40. 5W30 won't show any difference. I was using 0W30 for 2 years before the recall and now using 0W40, after.

 

[sohanrd]

The L8T doesn't have DFM. As for the low temp oil viscosity, DFM (and AFM before it) is not active when the engine is cold. It's active when engine temp is above 165.

This is the point. If the ECU does not activate DFM/AFM below a certain temperature, it's probably because the oil (even the factory specd viscosity) isn't flowing fast enough at that temperature to operate the DFM/AFM lifters with the required timing margin and without risk.

Now imagine using a thicker oil in the same engine.

If DFM/AFM still activates at the same threshold (165F), then you are sending an even higher viscosity oil through the same tiny control passages and lifter valves, oil that the engine already avoided using at lower temperatures with the original grade.

On the other hand, IF the ECU is intentionally waiting until the oil thins out enough to safely run DFM. If you increase viscosity, you reduce that safety margin at the exact moment the system expects fast hydraulic response.

 

[sohanrd]

There is no danger to the DFM using other oils besides 0W20. GM has us who passed the PICO test using 0W40. 5W30 won't show any difference. I was using 0W30 for 2 years before the recall and now using 0W40, after.

My question is: how do you actually know that 5W‑30 won't show any difference? Has anyone measured oil flow or response time at the DFM valves across different temperatures, RPMs, oil pressure levels?

Does "won't SHOW any difference" mean it also won't have any risk issues?

 

[Vladimir2306]

Exactly, 0W‑20 has more to do with the DFM system than with CAFE imo. DFM needs quick oil‑pressure changes to operate correctly, even at low temperatures.

Thicker oil may provide better protection for bearings and other components, but it adds extra risk to the DFM system.

Thats why GM calls for 0W‑20 for all DFM engines in every country (whether they havet CAFE or not), and 5W‑30 for non‑DFM V8s in certain markets. People usually dont check this. They say the same motors use 5w-30 in other countries, which is not simple as it seems.

I dont think any of those YT/forum gurus have ever scientifically tested the effect of higher viscosity oils on DFM. Most of them just say, "I’ve used it for this many years and have this many miles,” Thats all.

Using 5W‑30 may not destroy lifters immediately. But DFM heavily depends on fast oil flow. Dirty oil, cold mornings, slow oil flow, higher viscosity can catalyze those issues when the right combination hits.

That said, using 5W‑30 on a DFM deactivated (via OBD) engine could be beneficial. But I dont know, I could be wrong.

my 2c.

Disabling the DFM system, via OBD, does not give any results, as well as using Range systems. The DFM still remains in the engine. The only option is to completely remove the system at the aggregate level.That's right, using 5-30 oil on the 5th generation leads to problems with hydraulic compressors on runs of 100,000 miles and beyond. It is clear that in light of the problems with the L87 engine, the problem with the hydraulic compensators is not so acute, but nevertheless, we already have such cars that went to 5-30 and 0-30. In fact, switching to 0-40 oil is an even worse situation with hydraulic compressors, but I think GM is doing this on purpose, trying to delay the big problem, the destruction of the liners and crankshaft. Choosing the lesser of evils, so to speak.

 

[Silverado4x4]

This is the point. If the ECU does not activate DFM/AFM below a certain temperature, it's probably because the oil (even the factory specd viscosity) isn't flowing fast enough at that temperature to operate the DFM/AFM lifters with the required timing margin and without risk.

Now imagine using a thicker oil in the same engine.

If DFM/AFM still activates at the same threshold (165F), then you are sending an even higher viscosity oil through the same tiny control passages and lifter valves, oil that the engine already avoided using at lower temperatures with the original grade.

On the other hand, IF the ECU is intentionally waiting until the oil thins out enough to safely run DFM. If you increase viscosity, you reduce that safety margin at the exact moment the system expects fast hydraulic response.

You have it backwards, 0w20 or any synthetic oil is thinner on cold starts and thickens to 20 after getting to operating temperature for synthetic oil. Conventional oil is thicker when cold and thins out when warm. So on cold starts your synthetic oil is thinner on the cold start and thickens to 20 after getting warm.