67-81 GM viscosity chart

[ka9mnx]

Originally Posted By: Chris142
Originally Posted By: Dave1027
I think it's odd that they have 10w30 going past 100 degrees F but 5w30 only goes to 60 degrees? The first number is for cold engine. At operating temps, both oils are 30 weights.
the owners manual for my 2002 jeep is the same


All of my old car manuals limit 5w30 to 60F (shearing). That includes my 1993 F-150. And I remember GM recommending 20w for their engines in the 60's. As I remember, it was hard to find 5w30 in the stores until the late 80's (shearing). 10w-40 was very common until the mid 80's when GM banned it for their engines (shearing/sludge).

 

[Franz]

5w20 was a so called "ARCTIC oil" it was for year round use in freezing temperatures aslo were some 5w30s. I have a Shell SYNARCTIC 5w20 oil can in my Collection! Remember that was back in the 70s! An exception was the full synthetic mobil 1 5w20, the low viscoitys Goal was to lower the friction of internal engine parts to cut fuel consumption a bid, the first so called ENERGY CONSERVING oils! Here in europe the first 5w20 for year round use was Shell Helix Ultra X it was a Derivate of Shell´s single grade 20 for the F1 ferarris in 1996!

 

[Gokhan]

Originally Posted By: NH73
I tell some people I am doing 10,000 mile OCI with my Toyota and they think I am going to ruin my engine.

My 1985 Corolla owner's manual recommends 10,000 miles or 1 year on SF or SF/CC oil.

 

[Gokhan]

Originally Posted By: ka9mnx
All of my old car manuals limit 5w30 to 60F (shearing).

Again, it's not just permanent shear. Viscosity-index improver (VII) has no effect in the valvetrain or timing chain. As far as the valvetrain and timing chain are concerned, you're running 5W, not 5w30. That's because the extreme shear forces in the valvetrain and timing chain prevent the VII molecules from opening up and thickening the oil. This is called temporary shear. It's not as much of a concern in newer engines with roller cams, which have reduced wear by design.

 

[ZeeOSix]

Originally Posted By: Char Baby
NOTICE The Statement:
* "5W20 oil is not recommended for sustained high speed driving".

This^^^ was before these 5W20 oils were stout enough for those older vehicles. Today, it's a different story, isn't it?


I still wouldn't use 5W20 for "sustained high speed driving" ... ie, track use or similar.

 

[Shannow]

Here's a 1961 5W20 patent.

https://bobistheoilguy.com/forums/ubbthreads.php/topics/3860328/1961_5W20_patent...

Just to add to the thread, not comparing this to the 5W20s that you can buy now...nor in 1978.

 

[jhellwig]

Originally Posted By: maxdustington
Originally Posted By: jhellwig
It is 10w not sae 10. Two different things. Don’t ask me what it is but I just know it’s different.

The plot thickens!

7500 miles or a year is a long OCI for 1981, 3K OCIs are complete marketing. The truth comes out!


My 1984 impala owners manual said you only needed to change the filter every other oil change. Don’t remember the interval though.

 

[BrocLuno]

Originally Posted By: jhellwig
Originally Posted By: maxdustington
SAE 30 above 5 celsius good to know, you can use SAE 30 for most of the year.

5W20 is odd but I think SAE 10 is even more strange. You could run straight grades year round if you wanted to throughout the 70s apparently.


It is 10w not sae 10. Two different things. Don’t ask me what it is but I just know it’s different.


You still can, and some of us do

Oils have gotten a lot better, but a lot of multi-grades are still made the old way - start with 5 and add a ton of VII's to get to the high grade number. Still a 5 when all the shearing is done

 

[oil_film_movies]

Originally Posted By: Warstud
Originally Posted By: oil_film_movies
Originally Posted By: Warstud
What the heck is a 20w20?

The "20w" simply meant it had a cold viscosity (J300 spec, you know) measured in some standard device to simulate starting an engine.
Obviously a "20w" would be thicker than a "5w" when very cold; i.e., harder starting; your starter motor turns over more slowly cold.

Then, the "20" part is just another part of the J300 spec defined as a low-shear viscosity (how thick it is) at the temperature of boiling water by definition.

After all that, think how they made a 20w20 vs. a 5w20: A 5w20 needs more of the fragile VII chemicals, since you need thin base oils to meet the "5w" cold part, but it must still be thick enough to be a "20" at high temperatures. (Remember VII chemicals thicken a base oil at high temperatures without affecting cold temperature viscosity much.)

A 20w20 needs less VII, so its more stable over time at high temperature, high speed driving, made with thicker base oils to start with compared to 5w20.


What makes it different from a SAE 20 ?


A 20w20 may or may not be the same as an SAE 20 oil.
With the old high-wax base oils they used in the 70's, the oil maker probably had to had some VII chemicals to get the "20w" cranking spec met, at the same time the "20" hot viscosity spec was met.

For example, using the old base oils which is the subject of this thread, an SAE 20 conventional oil off the shelf might have used GroupI with only a little GroupII oils, and they had too much wax in them so they were too thick for the "20w" cold viscosity spec.
On the other hand, if the SAE 20 oils was made with better base oils, such as PAO, POE, or modern GroupIII oils, then it would have no problem passing the 20w cold part, while being a 20 weight hot, with no VII's needed. I'd think a good modern GroupII could be both a 20w20 AND SAE 20 at the same time too, no VII's.

Key concept: Being an SAE 20 or a 20w20 says little to nothing about what base oils are used, and says little about whether the SAE 20 could actually pass the 20w cold spec. I could make an SAE 20 out of Olive Oil, but it probably would not meet the 20w cold visc spec!

 

[Garak]

Originally Posted By: ka9mnx
All of my old car manuals limit 5w30 to 60F (shearing). That includes my 1993 F-150. And I remember GM recommending 20w for their engines in the 60's. As I remember, it was hard to find 5w30 in the stores until the late 80's (shearing). 10w-40 was very common until the mid 80's when GM banned it for their engines (shearing/sludge).

I started using 5w30 year round around the late 1980s, for obvious climate reasons, not to mention my dislike of seasonal oil changes. The taxis got 10w30 year round, but there were no -40 C starts for them. I do recall the 10w-40 prohibition. 10w-40 was never used in the taxis, or previous Chevy vehicles by my dad, or on the farm.

He seemed to understand the notion of HTHS before it was even a "thing." He had no use for 10w-40, limited patience with monogrades given our climate, and recognised the difference between a 5w30 HDEO and a 5w30 North American ILSAC style PCMO, and had little patience for an HDEO in a gasser due to his concern to eke every bit of fuel economy he could, given fleet usage.