Engine Oil Summary.

[RayD]

If you could run a straight 30 in the car you would ...

Well, you "could" run a single weight oil in a car but I wouldn't.

I'm not sure about the SAE 30 starting point

Blair, at first you seemed to be saying if you could use SAE 30, you would.

I was agreeing it's the grade you would associate with engines.

I use it in a relatively new, low mileage, Honda engine albeit attached to the lawnmower.

I'm not sure about the starting point either ... I imagine when they began modifying engine oils they started with a SAE 30 but since then as you say they’ve probably found a more cost effective way of using something thinner and working their way up, which would account for it working it's way back down as it slowly falls apart.

Ray

[dapinky]

I'm not sure about the starting point either ...

Surely the starting point would be whatever grade the oil is when it comes out of the ground?

Oil is oil (I know there is differences, depending on the geological structure of the oil field etc), but i would have thought it all starts out at a 'standard' viscosity.

(but I'm not a geophysisist)

[Elanlover]

Blair, at first you seemed to be saying if you could use SAE 30, you would.

Ray

Yes, but what I meant was "if you could" - meaning if the engine was always at the same temp (start up, high revs, etc.) and the ambient air temp was constant, then you could run a single weight oil. I wasn't meaning that perhaps they were hard to find or the like. Sorry if that wasn't clearer. Some engines are run with single weight oils to great success but in the right conditions. Unfortuntately, most cars don't run in those "right" conditions, especially ours. But yes, SAE30 is a pretty good base point for an automotive engine oil in average climates. I did a quick google and it seems it is the lower rating from which the oil starts from and to which the polymers are added as nitroman stated.

As for what comes out of the ground, there's LOTS of different types of crude with varying chararcteristics. And, there's lots of different hydrocarbons in crude that get distilled out to form varying products like oils, fuels, etc. The hydrocarbons used for oils can have differing boiling points and those get separated out to form lubricating oils at different viscosity ratings. Some light, sweet crude can be safely burned for fuel straight out of the ground.

[Elanlover]

Interesting that only the SAE 40 goes to an ambient temperature above 86 degrees F. Here in Mississippi, the high temp is above that about 5 months out of the year. Also, why would the high-end ambient temp be the same for 10W30 and 10W40? I would have thought the 40 would be higher.

SAE 40 goes to 40C or 104F.

Why do the 10W30 and 10W40 go to the same temp? Probably due to the chart itself being a basic representation only (10W40 DOES protect at higher temps than a 10W30) and the fact that they both start from a 10 weight oil then additives are introduced. So, you're getting a 10 weight oil that has some of the performance capabailities of a 30 or 40 weight oil at higher temps. But, its not going to perform as well as a straight 30 or 40 weight thus the lower temp rating for those multigrade oils AND the difference between the 10w30 and 10w40 at higher temps will be no where near as great as that between a straight 30 and 40 weight oil.

[tigerdog]

Just an update to my previous post on the topic: Liqui-Moly (German producer of oils sold as Lubro-moly in the US) has changed the formulation of the current Synthoil 5w-40 from a full synthetic base to a heavily refined mineral oil base. If the cannisters are marked "Synthoil Premium" article #2040, it's the new stuff. As it turns out, this was true of the oil I put in Smaug last year. While I have no complaints with the oil's performance, I prefer a fully-synthetic base as insurance against carbon buildup in the turbo bearings from heat soak. Lubro-moly have a product, "Synthoil Energy" 0w-40 article #2049 (1L) or 2050 (5L), that uses a fully synthetic base. At least one oil forum that's analyzed it says it compares to Mobil 1 0w-40 but with a slightly higher cold viscosity. This may be the next selection when Smaug goes in for his annual oil change sometime in September.

[tigerdog]

Just a quick update: The Liqui-moly 0W-40 didn't like warm weather and traffic; Smaug's oil pressure dropped below my comfort zone. Next change was to Castrol Edge titanium 5W-30 better pressure especially from cold but still a bit low on the scale in SoCal heat and traffic. Time to change again; thinking of the Castrol Edge 5W-40TD.