So is 15w-40 a good sub for SAE 30?
Without going into a couple of paragraphs I'll condense.
K. I've got iirc 16 5.5 hp Honda powered air compressors,6 or 7 generators from 3500w to 6500w.
Every one of these machines run everyday. I've got 2 compressor motors with well over 10000 hours on them.
In warmer ambient temps I use rotella 15w-40 because I can buy 5 gallon pails which are required based on the volume of equipment.
I run everything on a 100 hour/2 week oil change interval.
Once I used a 0w-30 in a generator in the July 38c heat. In a single day the oil sump was low enough to trigger the low oil alert and shut off the generator.
I bought a pail of rotella on my way home from work that night.
Last week I tried qsud in the 5w-20 flavour since this winter has been brutally cold but I usually use 5w-30 super-tech,bought in 5 gallon pails.
In my experience fuel dilution is a real issue in every piece of equipment I own,so my 100 hour/second Saturday maintenance routine grew from the observation that more often than not the oil level got higher in a week,not less,so I dump it bi-weekly.
Compressors cost me 800 each. Due to fuel dilution I'm very confident wear increases in these small motors based on the simple splash lubrication system.
Oh,and 1/4 can liqui-moly mos2 every second oil change.
So yes. A 15w-40 hdeo is a suitable replacement for an sae 30,in most every application.