Yes, We Have No Delvac, A Tale of Two Oils...

Back in the day when I worked land surveying, one of the guys on the crew had an older brother who apparently was a perfectionist. One of his quirks was to get his old engine oil tested after changing it. After trying many different brands, he decided that Mobil 1 Delvac synthetic was the best oil. That got me started using it in the old Volvo wagon since we had just installed a rebuilt engine. So when we got the tractor, it got the same oil.  

This spring when I went to change the oil, there was less than half a gallon left and it takes five quarts. The bulk plant, where I usually get it had been closed, so I called first. Well it turned out they're open, but all out of Mobil 1 Delvac. So I checked the local auto stores and they were all out too. But then I noticed that one store had Mobil 1 Turbo Diesel Truck oil. What's the difference? Here's what I found on line...

Mobil Delvac 1 ESP 5W-40 is an advanced full synthetic oil specially fomulated for diesel engines that works to extend engine life, fuel economy potential, and deliver long drain capability for modern diesel engines operating in severe conditions. Rating CH-4, CI-4, CI-4 Plus, CJ-4, CK-4, SM,SN

Mobil 1 Turbo Diesel Truck 5W-40 is a full synthetic heavy duty diesel engine oil that helps to extend engine life while providing long drain capability and fuel economy for modern diesel engines operating in severe applications.  Rating CI-4 Plus,CJ-4,CK-4,SL,SM,SN

So they sound the same. Checked the operator's manual for the tractor and for diesel engine oil: API Service Classification CE or CD. The API oil classification system lists backward compatibility for current types of oil and CH and CL are compatible with CE and CD. So apparently both Mobil 1's are compatible, which begs the question, why have two oils that are so similar, they're seemingly for the same use. Then we see the labels on the containers...

Apparently the Delvac oil is for the big rig eighteen wheel truckers.

While the Turbo Diesel is reserved for monster pickup drivers towing huge trailers.

So I bought the Turbo Diesel, but it'll just have to remain incognito since it's for a compact utility tractor. BTW, the arrow points to the oil filter, easily accessible with side panel removed. I always fill the new filter half way up or so when changing the oil. This was another tip I got, from a Harley rider, hard to believe, and it keeps the engine from running without oil for the first few seconds when starting it up right after the oil change.