Are there any real downsides to using a HDEO oil? They are all gasoline approved (I believe...) Many forums recommend, for example, M1 TDT as being superior to M1 0w40, and Rotella T6 seems almost universally liked.
HDEO oils do not adhere to the ILSAC requirements. You will find no HDEO oils with the GF-4 or GF-5 rating. The specs for each are incompatible. Much more important for the HDEO user is the manufacturer specs the oil meets or exceeds...Mack, Cat, Detroit Diesel, etc. If an oil is good enough for those manufacturers, it is good enough for me.
I might run this oil in my NA Impreza this summer, but I don't understand the actual differences between HDEO OIL and "regular" car oil. What EXACTLY qualifies an oil to be HDEO?
I will update on the oil consumption after a few kmiles. It's well known for thinner grades to increase the oil consumption and I might have to try Rotella T6 full synthetic 5W-40 if it's excessive. It's selling for $19.50 per gallon at Wal-Mart. I would hate to switch back to a diesel-engine/HDEO oil though because my engine is running so well with the GF-5 oil.