2024 test6 productsEngine Oil & Fluids
Which Diesel Motor Oil Brand Wins?
A head-to-head test of 6 diesel motor oil options with the measured results for each. See how they ranked and watch the full test video. Shoppers cross-shopping heavy duty diesel engine oil, 2 cycle engine oil, 75w90 gear oil and rotella 15w40 land here for the head to head that settles it.
Budget pick
Rotella T6
Price shown in test: $23
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The measured results
Every number below is read straight from the test. Scroll sideways to see all measurements. Products are listed in the order they finished.
| Product | 70F flow speed, uncooked oil | Noack evaporative loss (200g/400F/2hr) | Lubricity wear scar, cooked oil | -40F cold flow speed, uncooked oil | 70F flow speed, cooked oil | -40F cold flow speed, cooked oil | Lab anti-wear additive package |
|---|---|---|---|---|---|---|---|
| 1Mobil Delvac$14 | 3.03 seconds, 2nd in its 4-way heat (behind Royal Purple 2.98, ahead of Rotella T6 3.08 and Schaeffer's 3.13) | 394.56 g to 387.81 g, 6.75 g evaporated, worst (most evaporation) of all six oils | 5.94 mm, worst (largest) of all six oils | slowest in its 4-way heat, no explicit time given ('really needs to get a move on it') | 1st place in its heat, took the win by a very small lead; the only oil with no change in flow speed after heat exposure | 4th (last) place in its heat, 'does not like the cold', no explicit time given | 1,451 ppm, lowest of all six oils |
| 2Rotella T6$23 | 3.08 seconds, 3rd in its 4-way heat | 404.6 g to 397.96 g, 6.64 g evaporated, narrowly beat Mobil Delvac (6.75 g) in their direct pairing but 5th-best of all six overall | 5.63 mm, beat Mobil Delvac (5.94 mm) but narrowly outperformed by Royal Purple (5.6 mm); 5th-best of six overall | 1st place in its heat at 134.2 seconds, distant second overall behind Hot Shot's (95.4 seconds) | 3rd place in its heat; flow speed slowed after heat exposure, unlike Mobil Delvac | 1st place in its heat at 142.8 seconds, distant second overall behind Hot Shot's (almost 108 seconds) | no specific ppm given in the summary; narrator says 'a little bit higher anti-wear additive content would make this oil even better', implying below average |
| 3Royal Purple Duraleck$30 | 2.98 seconds, 1st in its 4-way heat, 2nd fastest of all six oils overall behind Hot Shot's | 399.25 g to 394 g, 5.25 g evaporated, best at the time tested, ultimately 2nd-best of six behind Amsoil (4.14 g) | 5.6 mm, barely beat Rotella T6's 5.63 mm; 4th-best of six overall | 2nd place in its heat at 142 seconds | 2nd place in its heat | 3rd place in its heat this time, lost a step from 2nd place in the uncooked cold test; no explicit time given, described as trailing Schaeffer's 154.9 seconds | not the ppm leader; narrator describes anti-wear content as 'pretty low'; detergent/dispersant package 2,129 ppm, 2nd highest behind Schaeffer's |
| 4Schaeffer's$42 | 3.13 seconds, 4th (last) in its 4-way heat | 405.72 g to 399.49 g, 6.23 g evaporated, moved into 2nd place at the time tested, ultimately 4th-best of six | 5.27 mm, by far the best at the time tested, beat Royal Purple; ultimately 2nd-best of six overall behind Amsoil (5.22 mm) | 3rd place in its heat, no explicit time given | 4th (last) place in its heat | 2nd place in its heat at 154.9 seconds, held up well after heat exposure, improved from 3rd to 2nd relative to Royal Purple | 2,042 ppm, 2nd-best of six behind Amsoil (2,129 ppm); highest detergent/dispersant package of all six oils at 2,141 ppm |
| 5Hot Shot's Blue Diamond$55 per gallon | 2.46 seconds, fastest of all six oils overall; easily beat Amsoil in their direct pairing | 410.85 g to 405.33 g, 5.52 g evaporated, 2nd place at the time tested, ultimately 3rd-best of six overall | 5.51 mm, 2nd place at the time tested, ultimately 3rd-best of six overall | fastest of all six oils at 95.4 seconds, a 'huge win' over Amsoil | easy win over Amsoil in its heat; placement vs the four-oil group not stated | fastest of all six oils again at almost 108 seconds | no specific ppm given; narrator calls the package 'a little bit light' though it performed well on the lubricity test |
| 6Amsoil Diesel Oil Signature Series$58 | no explicit time given; lost decisively to Hot Shot's (2.46 seconds), 'doesn't have a chance' | 418.91 g to 414.77 g, 4.14 g evaporated, best (least evaporation) of all six oils, 'very impressive' | 5.22 mm, best (smallest) of all six oils, 'very impressive' | no explicit time given; lost badly to Hot Shot's, 'not liking the cold temperature' | lost easily to Hot Shot's again, no explicit time given | no explicit time given; 'still struggling', about halfway down the track when Hot Shot's finished | 2,129 ppm, best of all six oils; detergent/dispersant package 2,048 ppm |
How it was tested
- flow speed at 70F, uncooked oil (seconds through a flow tester)
- Noack volatility / evaporative loss test, 200g oil heated to 400F for 2 hours (g evaporated)
- lubricity / film strength wear scar test on cooked oil under a wheel-and-pin tester (mm wear scar)
- cold flow speed at -40F, uncooked oil after 24hr freezer soak (seconds)
- flow speed at 70F, cooked (heat-exposed) oil re-test
- cold flow speed at -40F, cooked oil after a second 24hr freezer soak (seconds)
- independent oil analysis lab report: detergent/dispersant and anti-wear additive levels (ppm)