Choosing the right oil for your truck’s engine today means considering a lot more factors than in the past. For example, trucks built after October 2002 come equipped with mandated low-emission engines and they require API (American Petroleum Institute) CI-4 or CI-4 Plus oils specifically formulated for them. Meanwhile, trucks built before that date can use the new CI-4 oils as well as oil formulated for pre-’02 engines.

Another decision owner-operators need to make is whether to use synthetic engine oil or one formulated from mineral base stocks. The main issue in making this choice is price, as synthetic oils are around three to four times more expensive than mineral oil-based lubricants, points out Dan Arcy, technical marketing manager for Shell Rotella-T heavy-duty engine oil.

Arcy contends there are a lot of operating environments in which that extra premium may be well worth it, in terms of preserving a truck engine’s performance over the long haul.

“We believe the extra cost of a synthetic is justified in colder temperatures because of the startability issues and improved engine protection,” he tells DRIVERS. “Also, the faster you can get oil to engine components, the better you are going to protect the engine. If you are doing this, which is what a synthetic is designed to do, you should have less wear and longer engine life.”

”Synthetics have an advantage in extremely cold or hot operating environments,” says West Alexander III, senior staff engineer-engine oil technology for ChevronTexaco. “In normal operation, the rate of base oil degradation (due to oxidation and nitration) can affect drain intervals, deposit control, wear rates, fuel economy, soot dispersancy, viscosity control, etc.,” says Alexander. “Our field testing has demonstrated equivalent performance for properly formulated synthetic and mineral engine oils with the same performance category, but the advantage goes to synthetics on extremely low temperature cold starts.”

Chemistry class
So what makes synthetics perform so differently – and cost so much more – than regular engine oil?

“When referring to an engine oil as synthetic or mineral, we are referring to the base oil that is used to formulate the engine oil,” says Alexander. “In the past, synthetic engine oil was completely man-made, while mineral base oil was completely naturally occurring. However, modern technology has blurred the line of demarcation between the two.”

He notes that API and Association Technique de I'Industrie Europeenne des Lubrifiants (ATIEL) have established several categories respectively for base oils, with categories one through two defined as mineral base oils and categories three through six as synthetic base oils. Category six for both API and ATIEL is for polyalphaolefins (PAO), which is the most commonly used synthetic base stock. The designation “Group Five” is the “catch all” category for base stocks that do not meet the requirements of the first four categories, he says.

The real key to determining just what kind of engine oil performance you want, says Alexander, is looking at the kind of base oil it’s made from and its additive package. “The additive package is formulated to enhance the performance of the base oil, in terms of wear protection, viscosity, etc.,” he explains.

Switching oils
One of the long-standing myths about choosing synthetic or mineral-based engine oil is that the truck owner would be bound for the duration of truck ownership to their choice. That is, you could not switch back and forth between synthetic and mineral blends without harming the engine. But thankfully, that’s just not so.

“Synthetic and mineral products from the same manufacturer are compatible and can be switched back and forth,” says ChevronTexaco’s Alexander. “Compatibility between manufacturers is commonly OK but there are exceptions.”

“You can opt for a synthetic and then switch back to a mineral oil without having to worry about any negative issues,” says Shell’s Arcy. “However that doesn’t mean you can extend your engine drain intervals just because you switched to a synthetic. This is a common misconception. The reason for changing your engine oil is contamination that results from dirt, soot and other byproducts that result from the combustion process. Synthetics get contaminated just as quickly as a mineral oil.”

The real key to determining whether you go with synthetic or mineral-base engine oil really comes down to your truck’s operating environment.

“If you operate your equipment at the extreme end of the temperature range, then you should consider synthetic engine oils,” says Alexander. “Under normal operating conditions, mineral-based engine oils are the most cost-effective option.”

“If you are in a situation where you are operating in climate extremes, there are benefits to be realized from synthetic motor oil,” says Arcy. “At Shell, we also like to recommend the use of synthetics if you are running a reefer system that is constantly being asked to kick on and off. That’s because you do not have to worry about it being too cold or too hot, and you do not have to be concerned with changing viscosity grades for different times of the year and different climates.”