Current 10w-40 Minerial Base oils Cause Problems?

[edge10]

I have a two older performance cars and older small air cooled engines that spec this oil. I think in the 80's there was claim by some auto and small engine OEMs that 10w-40 grade could cause ring sticking due the added VI improvers needed for the wider spread between the high/low temp viscosity compared to the other grades with a closer spread. I recall some OEMs would void the warranty if 10w-40 was used an it caused damage. The other problem was durability tests of the time between 10w30 and 10w-40 found that the 10w-40 would shear down to 10w30 grade in a short time, so there was little advantage in using the 10w-40.

Do the current formulations of the mineral 10w-40 reduced or eliminate ring sticking? Will the current crop of 10w-40 stay in grade after shearing? Lastly, are wider spread hi/low temp viscosity mineral oils more prone to sludging?

 

[Shannow]

Early 10W-40s would rubberise the sump etc.

I doubt that any brand-name 10W-40 is that bad in any way shape or form these days.

Magnatec 10W-40 is pretty much Oz' biggest selling home instal (and mechanic instal) oil, on pretty much anything petrol diesel, or turbo.

 

[aquariuscsm]

Originally Posted By: edge10
Will the current crop of 10w-40 stay in grade after shearing?


I did a uoa on M1 10W40 (although it`s a synth and not a dino) and it stayed in grade.

 

[getnpsi]

Followup: once an oil has fallen out of grade, what is going on with the VI compounds still resident but not clinging? Is that a possible makeup of sludge with moisture and acids?

 

[Shannow]

It can fall 0.1cst, and fall "out of grade", or whole numbers and stay "in grade" depending on where it starts...the grading is next to useless pretty well for that reason alone

That's what's so amusing about the thin/thick 20s, and their need for bolstering with 40s and the like...until 16, they couldn't shear to anything lower.

 

[supercity]

10w40 is almost always semi synthetic here. There is no straight dino 10w40.

 

[bmwtechguy]

The quality of the VI improver is going to be one factor that determines if the oil stays in grade. Usually partial syn oils such as a couple of the HM 10W-40's have need for LESS actual VI improver due to higher overall VI of baseoil mix, so that is another factor to consider.

If I had older cars and wanted or needed an inexpensive, yet excellent protection oil, I would skip conventional 10W-40 and use something like Supertech 15w40 for it's commercial certs, telling me it meets some serious manufacturer specs for performance such as wear protection, and cleanliness. Yet it costs only $10.37 a gallon here or 2.57/qt. everyday price at WM.

For cold season, something like Rotella 10w30 would be the ticket.

Modern conventional 10W-40's are just not my favorite, although way improved from the 10W-40's of the 70's and 80's, are not the best way to go for the money or protection in my experience and opinion.

For the original poster, I would definitely be looking at an HDEO of some type for the engines you mentioned, if you want to stay with conventional oil and have the best protection. No, conventional HDEO does not usually come in 10W-40 in the US, but other grades will work fine at appropriate ambient temps.

 

[bmwtechguy]

Also, if you really want to stay with 10W-40, the other oil I would consider would be Quaker State Defy 10W-40. Sometimes this oil goes on sale for $3/qt. Yes it is a HM oil, but if you can get past that, it has a good bit more anti-wear chemistry than other 10W-40 oils and being a part syn, would mean it likely has less of those VI improvers that are more prone to shear over time. I have a longer history with another HM oil, Maxlife 10W-40, yet have not used it in any small engines or older flat tappet engines, as there are better choices out there for those particular engines, IMO.

 

[gregoron]

To OP, what you are asking does make sense. I myself am trying to ween my car from 10W-40 conv since there are better alternatives. In fact, I'm planning on a 5w30 HM for its next OCI. But, for some reason my car likes the conv ST it is using right now. My oil consumption dropped from 1qt per 1k miles to 1/5 qt only. It also runs smoothly although I suspect that is so because it may be shearing to a 30 weight. Yet, my consumption is down - so maybe it's still in grade.

I'll see if the thinner 30 weight can maintain this. If not, back to what's working for my car.