Mobil 1 vs Supertech 5W-30: Full Synthetic and High Mileage Oil Compared

Introduction

If your vehicle has 75,000 miles or more on the odometer, you have probably wondered whether switching to a high mileage oil actually matters, or whether the regular full synthetic in the same brand is basically the same product in a different bottle. To answer that, four SAE 5W-30 oils went through a full comparison: Mobil 1 Full Synthetic, Mobil 1 High Mileage, Supertech Full Synthetic, and Supertech High Mileage.

The high mileage versions are formulated for engines over 75,000 miles and claim to condition rubber seals and prevent leaks. All four oils carry 10,000 mile wear protection claims, and the tests set out to check cold flow performance, wear protection, evaporative loss, and how each oil treats rubber engine components.

How We Tested

Samples of all four oils were sent to an independent oil analysis lab, which reported on the anti-wear additive package, detergent and dispersant content, and total base number. Containers were shaken before sampling so the additive package stayed properly in suspension rather than settling at the bottom.

Beyond lab analysis, the oils faced a series of hands-on tests: a cold flow test at minus 40 degrees Fahrenheit, an evaporative loss test with heated oil, a lubricity test measuring wear scars on a test bearing, and a rubber conditioning test using O-rings and tire rubber.

Price and Certifications

Prices shift often, but at the time of testing a 5 quart container of Supertech Full Synthetic and Supertech High Mileage each cost right around $20. Mobil 1 Full Synthetic and Mobil 1 High Mileage each ran right around $25 for 5 quarts.

All four oils are SAE 5W-30, full synthetic, and carry the API SP and ILSAC GF-6A ratings. The interesting certification detail: both Supertech oils carry the Dexos certification, while Mobil 1 Full Synthetic has Dexos certification but the Mobil 1 High Mileage version does not. If your vehicle is under warranty and requires Dexos oil, that is worth checking before you buy.

Cold Flow Test Results

Synthetic oil is supposed to flow better than conventional oil in extreme cold, so moving parts get lubricated sooner on startup. Fresh samples of all four oils were placed in a freezer set to minus 40 degrees Fahrenheit for 24 hours, then raced side by side.

The results were consistent across two runs, including a run with previously heated oil. Mobil 1 High Mileage won both races, flowing fastest out of the gate and holding a strong lead. Supertech High Mileage finished second both times, regular Supertech Full Synthetic was a close third, and Mobil 1 Full Synthetic trailed in a distant fourth. Surprisingly, the high mileage oils flowed faster than the regular full synthetics in both brands, and the Dexos-certified Mobil 1 Full Synthetic was the slowest of the four.

Evaporative Loss and Wear Protection

To simulate heat near the upper piston ring area, 200 g samples of each oil were heated for two hours at around 350 degrees Fahrenheit, similar in spirit to the ASTM Noack volatility test. Lower evaporative loss means less oil consumption over time.

The Mobil 1 oils clearly did better here. Mobil 1 High Mileage lost only 4.5 g and Mobil 1 Full Synthetic 4.55 g, while Supertech High Mileage lost 5.57 g and Supertech Full Synthetic 5.72 g. In both brands, the high mileage version evaporated slightly less than the regular synthetic.

The lubricity test measured film strength by comparing wear scars on a test bearing. Mobil 1 High Mileage came out on top with the smallest wear scar at 7.29 mm, followed by Mobil 1 Full Synthetic at 7.34 mm, Supertech at 7.4 mm, and Supertech High Mileage at 7.46 mm. The Mobil 1 oils showed slightly better base oil quality on both the lubricity and evaporative tests.

Lab Analysis Details

The oil analysis reports showed nothing concerning: no harmful metals in any of the new oils, with just 1 ppm of aluminum and iron, which is typical. Barium, boron, calcium, and magnesium showed up as detergents and dispersants.

Supertech oils carried roughly 500 ppm more detergent and dispersant content than the Mobil 1 oils. Supertech leans on a higher concentration of calcium while Mobil 1 favors magnesium. For anti-wear additives, Mobil 1 High Mileage led at 1,629 ppm, with Supertech High Mileage second at 1,546 ppm. Total base number, the oil’s ability to neutralize acids, was slightly better in the high mileage versions at 6.8 versus 6.7, and 6.7 is already a solid number.

Rubber Seal Conditioning

The first rubber conditioning attempt at 350 degrees was too harsh: none of the oils prevented new O-rings from hardening, since that much heat burns off some ingredients. The test was redesigned, adding 4 oz of new oil and heating to around 200 degrees Fahrenheit for two hours, then soaking the O-rings for about 12 hours.

A new, untreated O-ring measures 0.1225 to 0.1235 inches in diameter, weighs 1.91 g, and takes 137 g of force to fold over. After soaking: the Supertech O-ring weighed 1.86 g with no swelling and needed about 10 g less force to fold. The Supertech High Mileage O-ring kept its weight at 1.91 g, was slightly larger in diameter, and needed 124 g. The Mobil 1 O-ring weighed 1.87 g with no size change and needed 134.36 g. The Mobil 1 High Mileage O-ring also weighed 1.87 g, was very slightly larger than new, and needed just 129 g.

A second conditioning check used pieces of a roughly one-year-old tire rubber soaked for 12 hours and then air-dried for 3 days, measured with a durometer. The untreated control measured 79 hardness. Supertech Full Synthetic softened it to 68, Supertech High Mileage to 64.5, Mobil 1 Full Synthetic to 66.5, and Mobil 1 High Mileage to 65.5. The high mileage versions of both brands conditioned the rubber slightly better than their regular counterparts.

Which One Should You Buy

Overall, Mobil 1 High Mileage was the standout performer: best cold flow, best wear protection, lowest evaporative loss, and strong rubber conditioning. The one caveat is that it lacks Dexos certification, so if your engine is under warranty and requires Dexos oil, the Mobil 1 Full Synthetic with certification is the safer pick.

Supertech High Mileage is a strong value at around $20 for 5 quarts. It carried more detergent and dispersant content, posted the second-best anti-wear package, and softened tire rubber the most of the four oils. For older engines with over 200,000 miles, high mileage oil is a sensible choice to help slow or prevent oil leaks, though it may not stop existing leaks outright.

Conclusion

High mileage oil is not just marketing: in this comparison, both high mileage versions flowed better in extreme cold, evaporated slightly less, conditioned rubber a bit better, and carried slightly stronger anti-wear packages than their regular full synthetic counterparts. Mobil 1 High Mileage delivered the best all-around performance, while Supertech High Mileage offers excellent value for the price. Just confirm Dexos requirements for any vehicle still under warranty before choosing the Mobil 1 high mileage formula.