Mexico's petroleum industry is wholly government owned. Petroleos Mexicanos (PEMEX for short) manufactures, distrubutes and sells gasoline, in a state owned monopoly. PEMEX gasoline stations are common. They are franchise operations, with the franchisee providing the land the electricity and the manpower to operate the station. Some of the newest PEMEX superstations in central Mexico, have integral mini-marts, car wash, and lube and oil changing facilities. Three grades of gasoline are sold in Mexico:
NOVA
Novas, is the lowest grade of gasoline and also the most common. It is sold out of Blue dispensing pumps, and is popular with Mexican drivers because of it's price (usually a few pennies less per gallon than higher grades). Most heavily laden RV's cannot use Nova, becuase it's octane level is far less than even the lowest grade of US gasoline, and it's use causes severe knocking and piston damage. Contrary to popular opinion, Nova does not contain significant amounts of tetraethyl-lead.
Environmental pressures in the USA caused the lead additive market to dry up early in the 1980's, and subsequently, lead was phased out of Nova gasoline in the late 1980's. I use Nova only when I cannot avoid it. Curiously, running the fuel through a engine does not produce immediate results. It's only after a hundred miles or so, that the full effects of it's low octane begins to cause pre-ignition and detonation.
MAGNA SIN
This mid-grade fuel is sold from a bright green pump, and is Mexico's most popular unleaded gasoline. It's octane level is somewhere around 86, and is superior to the silver pump "Extra" which it replaced in 1990. Most vehicles will run acceptably on "Magna" (as it's popularly called in Mexico). However, some very heavily laden motor homes and tow vehicles can find themselves in a position where Magna Sin, is just "border-line" in preventing knocking and pinging. These vehicles will have to have their ignition timing adjusted to prevent engine damage.
PREMIUM
Mexico's newest gasoline, is also it's best effort to date. Unfortunately Premium gasoline is found only in larger towns and cities, and will slowly migrate outwards to medium size towns. Premium seems to have an octane rating that's higher than US regular unleaded gasoline. The superiority in octane and performance over Magna Sin, makes seeking out and filling your tank with this fuel a wise choice, when availability permits. Premium is unleaded, and like Nova, and Magna Sin,
Premium, does not seem to contain the Additive "MTBE" found in California fuels.
MEXICAN DIESEL
Mexican diesel fuel used to be so cheap that big freight trucks could haul their load from the border with Guatemala to the US border for under a hundred dollars. Even through the cost has multiplied to just over a dollar per gallon in 1997, diesel fuel continues to be a bargain, especially in comparison to Mexican gasoline, which costs slightly more than gasoline sold in the Uniteds States.
DIESEL SIN, is the new and improved version of the old yellow diesel that was sold until 1994. Even though the older fuel offered very high economy, it's high sulfur content was unkind to turbochargers, and electronic metered fuel circuits. The new fuel is less yellow, and is still held in high regard by RV'ers, who inevitably compare it to fuel found in the US. Mexican diesel is generally regarded as being superior to U.S. fuel, in every respect but cleanliness.
RV'ers who wish to utilize Mexican diesel fuel, should prepare for possible dirty fuel by installing a pre-filter ahead of the factory installed fuel filter. Fuel/water separators, such as the "Raycor" brand, are very popular in Mexico, and protect fuel pumps and injectors against water and particulate contamination damage.
You may find vendors of auxillary filters quite easily by referring to your telephone book yellow pages under "Filters, Warehouse". These specialty businesses provide truckers and farmers with filter elements, housings, hose, and other related parts.
Many seasoned travellers to Mexico, have found that protecting their gasoline powered RV, with a large gasoline pre-filter, makes perfect sense. Spin on filters, designed for diesel engines, work perfectly well with gasoline. Reducing the fitting size to the correct diameter will allow original fuel line hose to be retained. Generally, these very large filters (about double the size of a car oil filter) are installed in the fuel pump suction line, between the tank and the engine fuel pump. The location allows the filter to protect the fuel pump as well. This idea works every bit as good on diesel or gasoline engines. Don't worry about the filter restricting flow to the fuel pump. The area of the large filter allows for fuel flows that are indistinguishable from an unfiltered line. A good filter model is one that is referred to as a "Primary Filter" for a Detroit Diesel engine. The filter house personnel can provide a filter mounting base that is compatible with the spin on element.