3 Cheap Motor Oils That Actually Work

We may receive a commission on purchases made from links.

For an engine to work efficiently (or work at all, for that matter), one factor that has a huge bearing is the engine oil. This miracle liquid lubricates, cools, and cleans as it works. This is a lot to ask for from a liquid that many of us barely spare a second thought. When choosing an engine oil, there are plenty of great oil brands to choose from. But what if you're looking to save a few bucks? How do you choose a cheap engine oil that won't break the bank or your engine? 

While it's never a good idea to put poor-quality oil in your engine, there are some cheaper motor oils that actually work (although you should always make sure they comply with your engine's specifications.) Some budget-friendly oils offer impressive performance and can help to keep your engine running smoothly, efficiently, and reliably. However, not all oils are ideal for every situation. For example, some perform better in colder temperatures, and others have better anti-wear properties. This article looks at three cheap engine oils that are rated 15W-40 (the "W" stands for winter) and when they're worth considering.

Shell has been making engine oil for over a century. While having a rich heritage doesn't guarantee its products a place on this list, it does offer confidence in the quality of its products. And at just over $23 per gallon, Shell Rotella T6 won't break the bank either. A good test of an oil's quality is how it performs in the American Petroleum Institute's (API) engine wear tests. More specifically, how it compares to the APIs CK-4 spec for diesel engine oils. On average, the oil offered more than 50% wear protection as required to meet API standards. 

This is also a good oil if you live in a colder climate, independent tests showed this oil out performed many more expensive alternatives when it's low temperature viscosity was measured. In terms of additives, the oil – while not as "additive rich" as some others – still outperforms some more expensive oils. This is especially true in engine cleaning additives, where it achieved a count of 2,036 particles per million (ppm). However, it was at the lower end of the scale when considering anti-wear additives, although it still boasted a healthy enough 1,741 ppm. For comparison, a premium oil like Amsoil Diesel oil had a ppm of 2,129. 

Royal Purple's Duralec engine oil is another budget offering that exceeds CK-4 performance standards. It also performed well in our ranked list of popular diesel oil brands. The company might not have a long and distinguished history like Shell, but it has been specializing in the manufacture of synthetic oils and lubricants since 1986. The Texas-based company has built a reputation for producing high-quality lubricants with a dark "purple" color. While this didn't perform as well in low-temperature tests as the Shell Rotella T6 oil, it still outperformed more expensive oils like Schaeffer's Synshield Durability Advantage, an oil that costs about $10 more per gallon. 

As far as additives go, Royal Purple's oil also fares well. In tests, the oil was found to have cleaning/detergent additives of 2,129 ppm (by comparison, the Shell Rotella T6 had a count of 2,036 ppm). However, the anti-wear additives in this oil aren't as abundant as in more expensive oils and are lacking when compared to Shell Rotella T6, with a total of 1,688 ppm. The tests also showed this oil to be great at resisting evaporation (nobody needs their engine oil to evaporate away). One proviso here: tests on this oil showed that its "cold performance" was adversely affected after the engine oil had been cooked — okay, you're unlikely to deliberately cook your oil, but the point of the test was to show how engine oil reacted to heat. A circumstance that it faces every time an engine runs. 

Mobil Delvac is the cheapest oil to make the list, and although it works, for most people, spending a little more cash would be a better option. However, Mobil does know all about oil, having been in the business for over 140 years, and has a reputation for producing high-quality products. The problem with this oil is the price point. For comparison, a five-quart pack of Mobil 1 15W-50 comes in at $47.99, whereas a gallon pack of Mobil Delvac costs around $15. In terms of product quality, this price difference is noticeable in a couple of key performance areas.

The first point of note is its cold weather performance out of the featured oils; this one fared the worst. Another factor is the additives in the oil. Mobil Delvac was comparable to the other oils when looking at the detergent/dispersant additives, with a creditable count of 2,036 ppm (identical to the Shell Rotella T6 oil). The story is different when it comes to anti-wear additives, the oil has by far the lowest number with a count of 1,451 ppm. This was reflected in a metal-on-metal wear test, where it produced the largest wear scar of any oil featured. In short, while this oil undoubtedly works, it's best suited for low-demand applications — think older, low-performance engines or vehicles that see light, occasional use.