Cartagena de Indias
Synthetic, semi-synthetic, or conventional: what changes, what 5W-30 or 10W-40 means, and why synthetic holds up better in Cartagena's heat. The manual has the final say.
Engine oil is a base oil plus an additive package. What changes between conventional, semi-synthetic, and synthetic is the base: conventional comes straight from refining crude oil; synthetic is made with more uniform molecules, designed to behave the same whether cold or hot; semi-synthetic is a blend of the two.
The job is the same for all three: lubricate, cool, clean, and protect against corrosion. The difference is how long and under what conditions they do it well.
Hot oil gets thinner; if it gets too thin it stops forming the film that keeps the parts apart. A more uniform base loses less viscosity with temperature and oxidizes more slowly, so it keeps protecting for longer when the engine runs hot. In an engine that spends the day idling with the A/C on, as we explain in the intervals guide, that difference matters.
That doesn't make conventional oil a bad oil: if your manual allows it and you change it on time, it does the job. What you shouldn't do is stretch the interval because "it's synthetic." The engine manufacturer sets the interval, not the oil's base.
The SAE grade describes viscosity, not quality. The number before the W (for winter) tells you how the oil flows when cold: the lower it is, the easier the engine starts cold. The number after the dash tells you how much viscosity it keeps at the engine's operating temperature: a 30 is thinner than a 40.
In Cartagena there's no such thing as a "cold" morning, so the first number matters less than in Bogotá; the second is the one that defines protection with the engine hot. But the choice isn't yours or ours: every engine is designed for a grade. A Kia Rio 2022 calls for 5W-20 and a Duster 2018 something else. What the manual does sometimes allow is a table of alternative grades by ambient temperature: that's where the climate comes in.
Besides the grade, the manual calls for a performance standard. The most common one in gasoline cars is the service category defined by the API. According to the American Petroleum Institute, the most recent category for gasoline engines includes the properties of all the previous ones: if your manual calls for API SN, an API SP oil gives you full protection. The same goes for the ILSAC GF-6 standard, designed for modern direct-injection and turbo engines.
The rule API itself gives is the same one we give: check the owner's manual first, then the charts. An expensive oil of the wrong standard is no better than the right one.
In our mobile oil change we use the grade and the standard your manual specifies, from recognized brands backed by the distributor. The change starts at COP $180,000 with synthetic oil and filter included; see what's included and what's charged separately. If you don't know what your car calls for, look it up by model and year or message us and we'll check it with you.
Checking terminals, cabin filter, wiper blades and fluid levels needs no lift and no workshop: it's done wherever you have the car parked, in Cartagena and nearby.
That the most recent API category for gasoline includes the previous ones (API SP covers what SN calls for), that ILSAC GF-6 covers modern engines, and that the owner should check the manual first come from the American Petroleum Institute's oil categories page. The explanation of the SAE grade (W = winter, first number cold, second hot) is the general definition of the SAE J300 system. That a synthetic base loses less viscosity and oxidizes more slowly in heat is a qualitative industry statement: NO percentages, temperatures, or kilometers of service life are published.
