Originally Posted By: ahoier
Well, really, that's the only reason I can think of for running 'diesel' or "HDEO" oil in a gasoline engine.....
As I pointed out, there certainly are other reasons for running HDEO in a gas engine. My gasoline Audi specs 15w-40 for the widest range of temperatures. What 15w-40 do you know of that is commonly available that isn't HDEO? Also, on vehicles that specify a wide range of viscosities, particularly those before manuals started printing 5w-20 or 5w-30 only and the like, HDEOs often fit within what's called for. Also, you're forgetting mixed fleet usage, which is one of the primary intentions behind having a dual rating.
Originally Posted By: Gokhan
All this means is that for 15W-40 C-service (diesel) oils like Chevron Delo, Mobil Delvac, Shell Rotella, etc., some of the performance tests for gasoline engines are not required and these oils may have incorrect (typically excessive) amounts of additives, which may cause emission-systems-component poisoning (such as catalytic-converter or Ox-sensor poisoning [destruction by chemical reaction with the additives]) in gasoline engines, leading to high emissions, engine problems, and expensive repairs, as cautioned explicitly by API in Footnote (d).
I know perfectly well what API markings are. However, for the most part, you are correct. However, also read the tables to which the footnotes apply, rather than just the footnotes themselves. If you read the table itself, you'll see that "oddball" grades such as 10w-40 and 20w-50 are also exempted from those standards, the same as HDEO. 10w-30 also has a different set of standards than does 5w-20, 5w-30 and so forth.
As for damage, we are talking about potential. How much of this has been realized? We don't see cars needing new cats left and right, even those that operated on older oil standards. Further, if a car drinks oil like there's no tomorrow, I doubt that having the reduced ZDDP content of an SM/GF-4 or SN/GF-5 oil is going to help much. The cat will be fouled, and ZDDP will be the least of its problems.
Beyond that, you are missing my point to use properly specified lubricants for your application, whatever that application is. For example, the 2006 Chev pickup I service requires, of course, a viscosity of 5w-30, and by its year, would call for SM. It also calls for GM's proprietary standard.
So, let's say I had my heart set on an HDEO, but I wanted to follow the manual. All I can think of off the top of my head for a 5w-30 HDEO is Esso XD-3 5w-30. Viscosity is 5w-30, check. API rating is SH, so we have a problem. It's certainly not going to meet GM's proprietary standard, so that selection is out.
Everything else is the wrong viscosity, even those that meet SM, and none of them meet the GM numbered specification. When I change oil in that truck, I look for exactly what the manual calls for: a 5w-30 viscosity, SM/GF-4 certification, and GM's numbered specification.
I simply don't know of any HDEO that meets all three standards, so I don't use it. It's not that HDEO itself is harmful; it's not going to be any more harmful than any out of spec oil.
I'm not going to buy a new Vette and run HDEO in it. That being said, I have no problems with running HDEO in my 1984 F-150 or my Audi, since it meets all specifications for both vehicles. Neither vehicles are heavy burners by any stretch of the imagination, and the F-150 doesn't have a cat to "poison."