Not this again, which engine oil?

[shadetreemechanic]

Its true that a thinner oil will reach the lifters better but its mainly important for cold starts. Even a 60 weight is just fine when warmed up.

The main reason they spec 30 weight in the US is due to CAFE regulations and its used since most engines will go the entire warrany period without issues. Your link mentions HTHS which is measured at 150 degC. Have a look at the huge difference in HTHS between a 30 and 50 weight.

The owners manual was recommending an ILSAC GF2 rated oil which is an eco spec (ILSAC GF spec is labelled "resource conserving"). Otherwise use 15w40 or 20w50 so the initial 30 weight recommendation is purely for fuel economy reasons.

 

[Jxfwsf]

If a lifter additive doesn't rectify a noise then it's nothing the viscosity will fix (even the bottles say they don't magically fix mechanical failure) regardless of how quick/slow it gets there.
I always thought the general rule of thumb was pushrod engine >20WXX, ohc <15WXX, then you take in the year the engine was manufactured and what bearing/machining tolerances were used at that time to suit.

buick/ecotech v6 vs alloytec... machining, metals, tolerances, technology and the machinery used to make the engine depend on what it should be running, sure a lighter weight oil will get to the lifters quicker but will it provide the lubrication requirements of the lower bearings?

 

[BlackoutSteve]

The 30 weight recommendation has been around since the 60's and perhaps earlier. Long before CAFE standards were introduced in 1975.

It would be interesting to see what the HTHS is at a lower temp such as 100°C as 150°C is a temp your oil will never see and the last thing you'd be worried about if it did.
Anyway, this link shows the 30 to have a number of 2.9 verses 3.7 for the 50 (+28%). Oil Viscosity Explained
"High-temperature high-shear-rate (HTHS) viscosity is an indicator of an engine oil's resistance to flow in the narrow confines between fast moving parts in fully warmed up engines."
I'm assuming the lower the number the better. I can't see how more resistance to flow could ever be preferred.

30 weight "purely for fuel economy reasons"? I doubt that.
Like I said, 30 weight was still the standard during the Big Three's horsepower wars of the mid-late 60's/early 70's when no one gave a crap about fuel economy.

The bearing clearances have pretty much always been 0.001" per inch of diameter. Nothing much has changed.
I think people assume the use of heavier oils in older engines because they assume that they have been worn to larger bearing clearances. Open up a 400K engine and take a measurement. I did and the 0.0003" (3 tenths of one thou) thick top layer of tin was still on every bearing shell.
Even guys with newly rebuilt old engine are still stuck in this old-engine-thinking and continue to use 25W50 that they didn't need to use in the first place. If they read their manual, even of their older cars, they would see 30 weight. My 69 Chevy's owner's manual lists the 30 weight part number.
A thicker oil will help reduce oil consumption, but that's due to worn rings and seals.

A thicker oil won't help keep bearings apart. It's the hydrodymanic oil wedge that does that. Not the viscosity.

 

[Jxfwsf]

These engines could benefit with a zinc additive but that'll screw sensors (and hurt captain planet), they run huge tolerances with tri metal bearings in a cast iron block, hell they'd last millions of km's if we still had leaded fuel.
At the end of the day it's old technology designed to run on older (and getting to be obsolete) oils.

 

[VR38]

Opposite.
Roller lifters and V6/LS crank driven oil pumps are designed for 30 weights and light winter grades.
Even Penrite with their backward "extra ten" way of thinking will still tell you to use a thinner grade if your lifters are ticking. Because if flows to the lifters better.
30 grade has been the GM standard for decades. In the owner's manual, only if 30 is unavailable, is there the suggestion of 40 or 50. In other words... 30. Why all these toffee grades as first choice?

Summer and winter is irrelevant. Unless you've pulled out your thermostat, your engine will run at almost exactly the same temp all year around.

Not quite opposite, a "thicker oil" will remain insitu longer that a thin oil, retaining some protection at start up but yes, fully agree, a thin oil, albeit at reduced pressure, will produce a quicker oil film on cold start up.
It really comes down to which is more usable (to the bearing or lifter) flow v's pressure?

FWIW in freezing conditions on a cold start (well any ambient temperature below the operating point of the thermostat for that matter) the thermostat CAN NOT maintain almost exactly the same temp all year around until the engine has had a chance to warm up.

 

[VR38]

All manufactures and oil companies agree, majority of wear happens at start up.

 

[BlackoutSteve]

The thicker oil sticking on parts for longer idea is point mute.
When an engine cools down, ALL oils become way too thick and will adhere to parts in the same way anyway.
Get an engine that's been sitting in a wrecking yard for 20+ years. Remove the oil pan and pull a main or rod cap. You might be surprised that there will still be plenty of oil in the bearings, Just like oil (or water) sandwiched vertically between 2 pieces of glass, -it's not going anywhere.

When it comes to start up, correct, of course it's impossible for a thermostat to maintain engine temperature, which is why I'm scratching my head at your suggestion of very thick 15-20 Winter grades.
Don't assume that a winter grade is actually has a viscosity of 15-20 when it's cold.
At ~20°C, even a 0W30 has an actual viscosity of about 40. What do you reckon it's viscosity might be during an overnight low of 0°C?

Next time you do an oil change, be careful, but try to do it when the engine is at it's normal operating temperature. Notice how "thin" the oil is and how well it flows out of the oil pan.
Then when refilling, compare the viscosity of your cold 15-20WXX that you assume flows well enough, and notice the massive difference. When refilling. I bet you have to keep stopping to prevent the funnel from overflowing because it's so thick and moves so damn slow.
So, there is absolutely now way it can be pumped around the engine anywhere as easily and do it's job as well like when it's up to temp. Even a 0WXX is still much thicker.

There is no motor oil available anywhere that has a viscosity low enough for cold starts, or one that doesn't require light throttle/low load warming up to the "correct" viscosity.

 

[shadetreemechanic]

The 30 weight recommendation has been around since the 60's and perhaps earlier. Long before CAFE standards were introduced in 1975.

It would be interesting to see what the HTHS is at a lower temp such as 100°C as 150°C is a temp your oil will never see and the last thing you'd be worried about if it did.
Anyway, this link shows the 30 to have a number of 2.9 verses 3.7 for the 50 (+28%). Oil Viscosity Explained
"High-temperature high-shear-rate (HTHS) viscosity is an indicator of an engine oil's resistance to flow in the narrow confines between fast moving parts in fully warmed up engines."
I'm assuming the lower the number the better. I can't see how more resistance to flow could ever be preferred.

30 weight "purely for fuel economy reasons"? I doubt that.
Like I said, 30 weight was still the standard during the Big Three's horsepower wars of the mid-late 60's/early 70's when no one gave a crap about fuel economy.

LOL, I think you're talking about a monograde 30 weight back in the 60s!!! Holden (and GM in the states) introduced a requirement for ILSAC GF2 10w30 around about when the VT came out.
If you don't believe the fact that the oil is for economy look up ILSAC....dunno what else I can say to that....
And the HTHS test is specifically carried out at 150 degC. Why would they test something that as you say, "your oil will never see"???

The bearing clearances have pretty much always been 0.001" per inch of diameter. Nothing much has changed.
I think people assume the use of heavier oils in older engines because they assume that they have been worn to larger bearing clearances. Open up a 400K engine and take a measurement. I did and the 0.0003" (3 tenths of one thou) thick top layer of tin was still on every bearing shell.

This I agree with. I never said anyone should use 25w50 or even 10w60.
With current synthetics the difference between all the 5w40, 5w30 and 0w40, 0w30 isn't all that much really so they're almost interchangeable. Some of these can be pretty stout as long as the HTHS is high enough. For an old Buick/Ecotec they're a bit on the thin side though and a 5w50 or 10w50 might be a lot more suitable.

 

[BlackoutSteve]

Straight 30? C'mon..
GM part number 9985183 for the 1969 factory Assembly Manual. Would you like a photograph of the page?
https://global.ihs.com/doc_detail.cfm?document_name=9985183&item_s_key=00394604

I'm also not saying the 10W30 isn't better for economy. I'm sure it is, but it's not chosen "purely for economy" like you suggest.

Do you honestly think your oil is reaching 150°C/302°F on a regular basis while your coolant is ~100°C/212°F ?
If it ever did, it would be rarely and for an instant.

 

[shadetreemechanic]

Straight 30? C'mon..
GM part number 9985183 for the 1969 factory Assembly Manual. Would you like a photograph of the page?
https://global.ihs.com/doc_detail.cfm?document_name=9985183&item_s_key=00394604

I'm also not saying the 10W30 isn't better for economy. I'm sure it is, but it's not chosen "purely for economy" like you suggest.

Do you honestly think your oil is reaching 150°C/302°F on a regular basis while your coolant is ~100°C/212°F ?
If it ever did, it would be rarely and for an instant.

Well we all know how much GM loves to supersede part nos. Is your manual actually from 1969?? And a modern (even ILSAC spec) 10w30 is much more preferable than a straight 30 obviously.

The thing is that certain engine parts do reach temps as high as that. In fact even bulk sump oil can reach temperatures as high as 130 or so since that's mentioned in the Nissan GT-R owners manual (they say dump the oil asap if it ever reaches 130 LOL)

edit: I did notice your link mentions 10w30 (with Zinc) so that oil has boosted ZDDP so that's a bit of a giveaway....