I like “diesel” oils. I’ve used a top-shelf “diesel” oil in my WRX for tens of thousands of miles. Mobil’s flagship oil is IMO Delvac1 5W-40, a heavy duty synthetic oil for high boost, high stress diesel motors and anything else with pistons in it. It’s a great oil. I only move away from it to use Mobil1 0W-40 instead depending on availability (I just don’t care which of the two oils I put in my car at this stage. Whatever’s on the shelf closest to me among those two choices, that’s what goes in the Subaru).
There have been discussions of the effects of zinc diethyl dithio phosphate on catalytic converters for ages now. Some say not to use HD diesel oils with high ZDDP in non-diesel motors to avoid catalytic converter fouling. Others say ZDDP levels don’t matter if the oil isn’t being combusted, and even if it is, go for it, potentially trading catcon longevity for motor longevity.
My 02 car has received all scheduled maintenance according to the owner’s manual, with oil change intervals around 5,000 miles (or more if I get lazy). After six years and after using a “diesel” oil, are the catcons poisoned?
RPM: HC Arnold CO Arnold
718: 20 100 0.03 1.0
2466: 20 130 0.14 1.0
(values in ppm; the "tab" isn't working to space stuff apart more, sorry).
My measured values were a bit above average but IMO still quite acceptable; so far, so good. Average HC is 17 and 12 ppm hi/low rpm respectively, and average CO is 0 (?!) and 0.1. Not bad IMO.
As the car ages I may end up seeing if ZDDP can poison my cats after all, but then again as time goes by less and less ZDDP is used in motor oils. Mobil just released an API SM turbodiesel 5W-40, and SM means it’s at least theoretically more catcon-friendly than the older SL formulation I’ve used for years now. As for the 0W-40, I’ve never given it a second thought as far as catcon health goes, since it’s a petrol engine oil anyway.
So there you have it. It’ll be interesting to see what happens in two years and since I tend to keep my cars and drive my cars into the ground, I’m likely to find out.