Oils

Doc's Diesel Engine Oils

Your Engine Is Only As Good as What's in the Pan.

Everything your diesel does—every cold start, every loaded grade, every idling job site hour—it does on a film of oil a fraction of a millimeter thick. That film is either up to the job or it isn't, and there's no middle ground at 1,000 degrees of turbo heat. Doc's Full Synthetic Heavy-Duty Diesel Oils are engineered for engines that earn their keep: maximum wear protection in severe operating conditions, from brand-new emissions-compliant rigs to the high-mileage workhorses that refuse to quit.

Built for Severe Duty, Not Just Rated for It.

Available in 15W-40 and 5W-40 full synthetic formulas, Doc's oil delivers an advanced additive system that protects critical components under high-load, high-heat conditions, excellent low-temperature pumpability for fast cold-start protection, and enhanced oxidation and thermal stability that fights sludge and deposits. Formulated to meet modern emissions standards while staying backward-compatible with older engines—one oil line for the whole diesel driveway.

Built to OEM Standards. Backed by Doc's.

Our oils meet or exceed major industry and manufacturer specifications, so running Doc's keeps your engine protected and your warranty intact. No guesswork. No BS.

Doc's Makes It Easy.

Check your capacity before you order—a 6.7L Cummins takes 12 quarts, a 6.7L Powerstroke 13, a 6.6L Duramax 10—or skip the math entirely with a Doc's Oil Change Kit that pairs the right oil and filter for your exact truck. Change every 10,000-15,000 miles for normal duty, 7,500-10,000 for severe service, and always per your manufacturer's schedule.

Free Shipping on All U.S. Orders $99+

Diesel capacities mean one oil purchase usually clears the line—everything over $99 ships free anywhere in the U.S. Your engine is only as good as what's in the pan. Fill it like you mean it.