# Why You Should Choose Lubri-Loy Monograde Diesel Engine Oil 40W (AEO-40) Over Southwest Oil Co. Endurance 40W Date: 2026-11-14 Canonical HTML URL: https://lubriloy.com/blog/why-choose-lubri-loy-aeo-40-over-southwest-oil-endurance-40w-diesel-engine-oil 40W DIESEL ENGINE OILAEO-40 # Why You Should Choose Lubri-Loy Monograde Diesel Engine Oil 40W (AEO-40) Over Southwest Oil Co. Endurance 40W Southwest Oil Endurance 40W alternative - **Lubri-Loy:** Monograde Diesel Engine Oil 40W - **Package:** 55 gal drum [Buy AEO-40 direct](https://lubriloy.com/products/aeo-40)[Request a quote](https://lubriloy.com/support?topic=quote&product=AEO-40) Southwest Oil Co. Endurance 40W in a 55 gallon drum has a direct counterpart on Lubri-Loy's interchange list: AEO-40, our Monograde Diesel Engine Oil, SAE 40, in a 55 gallon drum, available direct from Lubri-Loy. We could not find a public data sheet for Southwest's Endurance 40W, so this page lists the Lubri-Loy specifications and what to confirm against your engine maker's requirements. ## Quick answer Lubri-Loy's interchange list pairs Southwest Oil Co. Endurance 40W (55 gal drum) with Lubri-Loy AEO-40 (55 gal drum), a monograde 40W diesel engine oil meeting API classifications up to CI-4. 01Side by side ## Southwest Oil Co. Endurance 40W vs AEO-40 | Attribute | Southwest Oil Co. Endurance 40W | AEO-40 | | Viscosity grade | SAE 40 (40W) | SAE 40 (40W) | | API service | See Southwest Oil Co. label or data sheet | All API service classifications up to CI-4 (Lubri-Loy catalog) | | Military and OEM specs | No public data sheet found | MIL-L-2104F and MIL-L-2104G; suitable where Allison C-4 or Caterpillar TO-2 are specified; meets Caterpillar ECF-1 (catalog) | | Not for | See Southwest Oil Co. label | Caterpillar TO-4, two-cycle gasoline engines, aircraft engines, EMD diesel engines (catalog) | | Package | 55 gal drum | 55 gal drum (AEO-40); 5 gal pail is AEO-40-640 | Southwest Oil Co. does not publish a data sheet we could locate, so no competitor values are shown. Lubri-Loy values are from the Lubri-Loy catalog. Scroll the table sideways to see every column. 02The case for switching ## Why choose AEO-40 - 01 ### Buy direct, ship free AEO-40 is on lubriloy.com with a listed price and free US shipping. Net 30 terms are available by credit application. - 02 ### Wide diesel coverage The catalog says AEO monograde diesel oils suit nearly all two- and four-cycle diesel applications under mild to heavy duty, at any fuel sulfur level. - 03 ### Drum or pail Order 55 gallon drums for fleets and plants, or 5 gallon pails (AEO-40-640) for smaller users. - 04 ### Since 1949 Lubri-Loy has supplied lubricants since 1949. We source, formulate and package through our network of US blending partners. 03Before the changeover ## Check before you switch Monograde oils are specified for particular engines and operating temperatures. Check your engine maker's required SAE grade and API category before you switch. AEO-40 is not for Caterpillar TO-4 applications, two-cycle gasoline engines, aircraft engines or EMD diesel engines. Because we could not verify Southwest Oil Co.'s published specifications, compare your current label against the Lubri-Loy catalog sheet. 04Common questions ## FAQ ### What is the Lubri-Loy equivalent of Southwest Oil Co. Endurance 40W? + Lubri-Loy's interchange list pairs Southwest Oil Co. Endurance 40W (55 gallon drum) with Lubri-Loy AEO-40, a monograde 40W diesel engine oil in a 55 gallon drum. ### What API classification does AEO-40 meet? + The Lubri-Loy catalog says AEO monograde diesel oils meet all API service classifications up to CI-4. ### Is AEO-40 available in a pail? + Yes. The 5 gallon pail is AEO-40-640. ### How do I buy it? + Order on lubriloy.com with free US shipping, or call (877) 582-7456. Premium Lubricants, Without Premium Prices. ## Monograde Diesel Engine Oil 40W AEO-40 / 55 gal drum [Buy AEO-40 direct](https://lubriloy.com/products/aeo-40)[Request a quote](https://lubriloy.com/support?topic=quote&product=AEO-40) ## Sources Southwest Oil Co. and Endurance are trademarks of their owners. Product names are trademarks of their respective owners and are used for identification only. Lubri-Loy is not affiliated with or endorsed by them. Competitor figures are from the sources linked above; Lubri-Loy figures are typical values from the Lubri-Loy catalog. Always check the current data sheet before changing products. Premium Lubricants, Without Premium Prices.