In about 2005 I switched from 20/50 Valvoline to DELO 15/40 because I had a more or less unlimited supply from draining the residual after a delivery from the tankers I was driving. Eventually, I used the last of what I saved only to discover that Chevron had greatly reduced the metals in the additive package after diesels got trap oxidizers etc. So I began using an after-market additive at $15 a pint in addition to the DELO I got from COSTCO. I had been using DELO in my flat-tappet motorcycles too. So it's gotten expensive.
Motorcycle-specific oil from NAPA is about the same price as DELO with an additive. I'm pretty careful about oil for my Norton Commando as the tappets don't even rotate and I had two cams go flat on that engine. The last replacement was a work-hardened used one and I've had no trouble since. On my Mercedes diesel, the rockers ride directly on the cam so there's nothing to rotate and I've used the expensive additive package on that too. After 10-15 thousand miles the cam still looks good when I pull the valve cover to adjust the valves. So all appears to be well.
Lately I discovered that Valvoline Racing Oil has the metal additive package and is less expensive than, say Harley-branded oil and besides don't Harleys have roller tappets now too? So, I've been putting Valvoline Racing Oil in my 235 the past couple of changes.
Anyhow, it's good news that Rotella T4 15/40 has the zinc additive. Is it more expensive than DELO? I wonder if it would be OK in the Mercedes diesel.
