Oil viscosity recommendation

[Marky Dissod]

Does anybody actually know how long it takes for fuel dilution + contaminants to break down the oil to the point where it is no longer providing adequate protection?

As a rule of thumb I came up with myself, I've firmly come to believe that an oil change is slightly overdue when that particular engine
has experienced up to but no more than 0.50 Quart (473 mL) of oil consumption - less would be even better of course.

We hear a lot about fuel dilution and wear breaking down 0w20 to basically nothing,
but I never hear concrete numbers as to how long 0w20 would be considered good to use from the hardline 5w30 advocates.
I mean surely it doesn’t break down within 3k miles?

Most hardline 5w30 advocates simply accept that fuel diluted 5W30 will eventually experience viscosity breakdown as well,
eventually becoming 5w20, except the startup protection also gets worse too, but the other way, so, more toward 10w20.

It follows that if you start with 0w20 and fuel-dilute it, it will eventually become 'Toyota motor oil' - 0w16 or 0weven-less if the oil change interval goes too long.

If you check your oil often enough (weekly for me), you can use my homemade idea above; fuel-diluted oil is experiencing oil consumption by definition.

The 5.3L does fine on 0W20 but the more powerful 6.2L, especially when under high loads, experiences engine wear faster.

Same goes for 6.2L fuel dilution.

 

[PPV_2018]

I recall seeing posts at 5K miles with less than 1% dilution. Funny, back in the 1960's the big 3 suggested 6K intervals for oil changes. Hard to believe that things have gotten much worse since then.

Guidance from the 1960’s may not be the reference point that’s particularly relevant — I mean things have come so far since then. I do recall manuals for older vehicles I’ve owned like My ‘84 Buick and ‘85 Chevrolet saying 3000k OCI.

Or maybe it was 5k (3k may have been severe service), Now I don’t remember. But it wasn’t 6. So as we can see, standards change over the years.

As far as the dilution, I think it’s important to know what’s a realistic average number to

@Marky Dissod

I understand that all oil weights break down and get contaminated and possibly diluted, but I wish we had more reference data as a community to dissect and see how long ow20 is good for in a DI engine with cylinder deactivation.

That way we would have solid evidence on if ow20 would not lead to shorter engine life with low OCI, etc. Some people swear the 0w20 is a death sentence, others say that it doesn’t break down as fast as people think. I think just arbitrarily saying that Ow20 gets fuel diluted and will kill your engine is somewhat misleading if we don’t know the specifics.

Unless everyone sent off oil samples and posted them in a comprehensive thread, I guess we really won’t have a solid answer.

 

[Marky Dissod]

At least you understand that all oil weights experience viscosity breakdown, and that it is accelerated by fuel dilution.
(Some viscosity breakdown is simply due to mechanically / hydraulically squeezing motor oil through tiny passages at pressure over billions of engine revs.)

Will we ever have a quantifiable answer as to a rate of viscosity breakdown? Probably not.

"That way we would have solid evidence on if ow20 would not lead to shorter engine life with low OCI, etc.
Some people swear the 0w20 is a death sentence, others say that it doesn’t break down as fast as people think.
Just arbitrarily saying '0w20 gets fuel diluted and will kill your engine' is somewhat misleading if we don’t know the specifics."

Some people exaggerate when they're genuinely trying to help, precisely because of a lack of quantifiable data. Oh well.
Fact remains, if you understand how the Stribeck curve works well enough, you don't need data that you and I and others would genuinely appreciate,
to get that 0w20 leads to 'shorter' engine life compared to 0w30 given equal oil change intervals, even without cylinder deactivation, regardless of rate of fuel dilution.
Cylinder deactivation and longer oil change intervals also make things worse.

Qui bono?

 

[vcode]

....Guidance from the 1960’s may not be the reference point that’s particularly relevant — I mean things have come so far since then. I do recall manuals for older vehicles I’ve owned like My ‘84 Buick and ‘85 Chevrolet saying 3000k OCI.

Or maybe it was 5k (3k may have been severe service), Now I don’t remember. But it wasn’t 6. So as we can see, standards change over the years.

As far as the dilution, I think it’s important to know what’s a realistic average number to

@Marky Dissod

I understand that all oil weights break down and get contaminated and possibly diluted, but I wish we had more reference data as a community to dissect and see how long ow20 is good for in a DI engine with cylinder deactivation.

That way we would have solid evidence on if ow20 would not lead to shorter engine life with low OCI, etc. Some people swear the 0w20 is a death sentence, others say that it doesn’t break down as fast as people think. I think just arbitrarily saying that Ow20 gets fuel diluted and will kill your engine is somewhat misleading if we don’t know the specifics.

Unless everyone sent off oil samples and posted them in a comprehensive thread, I guess we really won’t have a solid answer.

My 1994 Z-28 calls for oil changes at 7500 miles with ancient SG conventional motor oil. Modern synthetics are light years better than SG.

 

[Marky Dissod]

My 1994 Z28 calls for 7500 mile oil changes with ancient SG conventional motor oil. Modern synthetics are light years better than SG.

As an OBD1 LT1 tuner, almost sure that your 16188051 pcm has a (relatively primitive version of an) Oil Life Monitor,
which would would very rarely if ever recommend 7500 mile oil changes.
Nonetheless, congrats on still owning a 94 Z28!

 

[vcode]

As an OBD1 LT1 tuner, almost sure that your 16188051 pcm has a (relatively primitive version of an) Oil Life Monitor,
which would would very rarely if ever recommend 7500 mile oil changes.
Nonetheless, congrats on still owning a 94 Z28!

Owners manual makes no mention of an OLM, only a low oil indicator. I've never had to reset anything. Manual just says to change at 7500 miles. Bought it used in 1995.....

 

[Marky Dissod]

Owners manual makes no mention of an OLM, only a low oil indicator. I've never had to reset anything. Manual just says to change at 7500 miles.
Bought it used in 1995 ...

Wouldn't be surprised if the owners manual made no mention of Performance Mode, or OverHeat Mode,
but those features exist and are tunable in any LT1 pcm - even if the vehicle itself does not allow the driver to use them.

Proud to state that several LT1 cars have been saved from overheat damage by tuning the OverHeat Mode parameters above and beyond GM OE programming.
(Maybe this is why I'm loathe to settle for 'GM OE' recommendations ...)

 

[vcode]

Wouldn't be surprised if the owners manual made no mention of Performance Mode, or OverHeat Mode,
but those features exist and are tunable in any LT1 pcm - even if the vehicle itself does not allow the driver to use them.

Proud to state that several LT1 cars have been saved from overheat damage by tuning the OverHeat Mode parameters above and beyond GM OE programming.
(Maybe this is why I'm loathe to settle for 'GM OE' recommendations ...)

Mine has started doing something strange in that both fans come on and won't shut off, even though the temp gauge reads normal.

 

[swathdiver]

The 6.2l has been running 0W20 for over a decade now and up until the recall we weren't seeing any non-DFM oiling issues to speak of.

Most of the 6.2 engines in the SUVs don't see high loads from racing or towing and we know the Gen V LT engines are not as enduring as the Gen IV LS.

Those that race the 6.2 engines use thicker oil. Those that tow with 6.2s in their pickups either experience early engine wear from running 0W20 or use thicker oil like the Corvette/Camaro guys.

 

[Marky Dissod]

Mine has started doing something strange in that both fans come on and won't shut off, even though the temp gauge reads normal.

The head temp gauge and the H2Opump temp sensor operate completely independent of each other (unless cleverly modified).
Your H2Opump temp sensor and/or its brittle wiring are likely compromised and need upgrade-replacement.
Until you do, the H2Opump temp sensor will report -40 to the pcm, meaning it may never go closed loop and will run rich til corrected.

 

[ZKWBQD]

Lets be honest, most people believe that GM has the engineering expertise to know what oil is correct for their engines, and there are others who don't. It's the same story for virtually every manufacturer out there and is unlikely to change.

The oil viscosity was pushed by the EPA, not GM. I once met a General Motors engine designer who did not like 0-20W oil.

 

[ZKWBQD]

So my 2020 YuKon XL with the 5.3 engine it says to use 0W-20 oil and in my former 2010 Yukon XL with the 5.3 engine. I ran 5W-30, and engine was still running smooth at 292,000km. What are you folks running in your 5.3 liter engines? Can I run 5W-30 in this one also, which is what I prefer to do.

Something has changed at the dealerships. A year ago, I had my Tahoe in for service and I requested synthetic 5W-30. They flatly refused. Last week, I was there again, and I requested synthetic 5W–30 oil. This time, they were HAPPY to do it. I asked why the change? They said "We now have a different EPA administration. The rule rules have changed."

 

[vcode]

Something has changed at the dealerships. A year ago, I had my Tahoe in for service and I requested synthetic 5W-30. They flatly refused. Last week, I was there again, and I requested synthetic 5W–30 oil. This time, they were HAPPY to do it. I asked why the change? They said "We now have a different EPA administration. The rule rules have changed."

Nothing has changed. There are proposals out there that have to go thru a public comment period. Then they have to withstand the numerous legal challenges that are most certain to happen. That could take years. And I have no idea why any of that would affect what oil they put in your truck.

 

[06 Yukon XL]

5.3L should still be using the 6 speed in 2020.

Yes mine is a six speed

 

[06 Yukon XL]

Thank you for all the replies, lots of good info. I think I will go with the 5W 30 as it worked well in my former 10 YukonXL. Was still purring nicely when traded at 292,000km. No cylinder deactivation.

 

[Bellazdad]

Sounds like you already know what you want. 5W30 will be fine. the 0W20 is recommended by the manufacturer to maximize fuel mileage. In reality the difference between the two is not that much.

A seasoned mechanic 38 years recommended since we hear valve/lifter slight sounds on cold start up, to switch to 50 weight oil. Whats the group think? This is on 2018 Silverado 5.3.

 

[Marky Dissod]

A seasoned mechanic 38 years recommended since we hear valve/lifter slight sounds on cold start up, to switch to 50 weight oil. Whats the group think?

38 year old engines were built to much looser tolerances than GM Gen3/4/5 V8s.
MIGHT consider 0w40 5w40 or 10w40 depending on engine mileage and how hot or cold it is outside when the engine first starts after 4hrs of being off.
THEN AGAIN ...
Since switching to Valvoline Restore & Protect 5w30, I still notice about 60 seconds of cold piston wap during any cold start om a winter day,
but not as loud as it used to be. Spring and summer, it's under 30 seconds, and only once a day.

 

[vcode]

A seasoned mechanic 38 years recommended since we hear valve/lifter slight sounds on cold start up, to switch to 50 weight oil. Whats the group think? This is on 2018 Silverado 5.3.

50 weight? I wouldn't. This isn't 1970.......

 

[Fless]

A seasoned mechanic 38 years recommended since we hear valve/lifter slight sounds on cold start up, to switch to 50 weight oil. Whats the group think? This is on 2018 Silverado 5.3.

Hard NO.