Hyundai Coupes/Sedans 1994-1998 Repair Guide

Fuel and Engine Oil Recommendations



Some fuel additives contain chemicals that can damage the catalytic converter and/or oxygen sensor. Read all of the labels carefully before using any additive in the engine or fuel system.

All vehicles covered by this guide are designed to run on unleaded fuel. The use of a leaded fuel in a vehicle requiring unleaded fuel will plug the catalytic converter and render it inoperative. It will also increase exhaust backpressure to the point where engine output will be severely reduced. Obviously, use of leaded fuel should not be a problem, since most companies have stopped selling it for quite some time.

For all Hyundai models, the minimum octane rating of the unleaded fuel being used must be at least 86 (as listed on the pumps), which usually means regular unleaded. Some areas may have even lower octanes available, which would make 86 a midgrade fuel. In these cases a minimum fuel octane of 86 should STILL be used.

Fuel should be selected for the brand and octane which performs best with your engine. Judge a gasoline by its ability to prevent pinging, its engine starting capabilities (cold and hot) and general all weather performance. The use of a fuel too low in octane (a measurement of anti-knock quality) will result in spark knock. Since many factors such as altitude, terrain, air temperature and humidity affect operating efficiency, knocking may result even though the recommended fuel is being used. If persistent knocking occurs, it may be necessary to switch to a different brand or grade of fuel. Continuous or heavy knocking may result in engine damage.

Your engine's fuel requirement can change with time, mainly due to carbon buildup, which will in turn change the compression ratio. If your engine pings or knocks switch to a higher grade of fuel. Sometimes just changing brands will cure the problem.

The other most important quality you should look for in a fuel is that it contains detergents designed to keep fuel injection systems clean. Many of the major fuel companies will display information right at the pumps telling you that their fuels contain these detergents. The use of a high-quality fuel which contains detergents will help assure trouble-free operation of your car's fuel system.


See Figures 1 and 2

The recommended oil viscosities for sustained temperatures ranging from below -20° (-30°C) to above 100°F (40°C) are listed in the section. The only oil type shown is multi-viscosity. Multi-viscosity oils are recommended because of their wider range of acceptable temperatures and driving conditions.

When adding oil to the crankcase or changing the oil and filter, it is important that oil of an equal quality to original equipment be used in your car. The use of inferior oils may void the warranty, damage your engine, or both.

The Society of Automotive Engineers (SAE) grade number of the oil indicates the viscosity of the oil-its ability to lubricate at a given temperature. The lower the SAE number, the lighter the oil; the lower the viscosity, the easier it is to crank the engine in cold weather, but the less the oil will lubricate and protect the engine at high temperatures. This number is marked on every oil container.

When using engine oil, there are two types of ratings with which you should be familiar: viscosity and service (quality). There are several service ratings, resulting from tests established by the American Petroleum Institute. The most current rating, SG, is recommended by Hyundai for use in all engines. No other service ratings are acceptable.

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Fig. Fig. 1: Oil viscosity chart

Oil viscosities should be chosen from those oils recommended for the lowest anticipated temperatures during the oil change interval. Due to the need for an oil that embodies both good lubrication at high temperature and easy cranking in cold weather, multigrade oils have been developed. Basically, a multigrade oil is thinner at low temperatures and thicker at high temperatures. For example, a 10W-40 oil (the W stands for winter) exhibits the characteristics of a 10-weight (SAE 10) oil when the car is first started and the oil is cold. Its lighter weight allows it to travel to the lubricating surfaces quicker and offer less resistance to starter motor cranking than a heavier oil. But after the engine reaches operating temperature, the 10W-40 oil begins acting like straight 40-weight (SAE 40) oil. It behaves as a heavier oil, providing greater lubrication and protection against foaming than lighter oils.

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Fig. Fig. 2: Look for the API oil identification label when choosing your engine oil

The American Petroleum Institute (API) designations, also found on oil containers, indicate the classification of engine oil used for given operating conditions. Only oils designated Service SG (or the latest superceding designation) heavy-duty detergent should be used in your car. Oils of the SG-type perform many functions inside the engine besides their basic lubrication. Through a balanced system of metallic detergents and polymeric dispersants, the oil prevents high and low temperature deposits and also keeps sludge and dirt particles in suspension. Acids, particularly sulfuric, as well as other by-products of engine combustion are neutralized by the oil. If these acids are allowed to concentrate, they can cause corrosion and rapid wear of the internal engine parts.