All vehicles covered by this guide are equipped with emission control systems that would be severely damaged or destroyed by the use of leaded fuels or additives. NEVER put any gasoline in your tank that could contain lead or you will likely void your warranty.
Fuel should be selected for the brand and octane which performs best with your engine. Judge a gasoline by its ability to prevent pinging, it's engine starting capabilities (cold and hot) and general all weather performance. As far as the octane rating is concerned, all of the engines covered by this guide are capable of running fine on a high-quality 87 octane gasoline (usually this is a mid or low grade in the U.S.). If necessary at high altitudes, most engines can also run on lower octanes, down to even 85. BUT, when you are working your van hard, such as towing or hauling a full contingent of passengers with luggage, it is recommended that higher octane will help maximize power while preventing damaging engine knock. If your van has the 4.3L (VIN W) CMFI or CSFI engine, it is recommended that you use a minimum of 91 octane gasoline whenever you are towing or hauling heavy loads.
Your van's engine fuel requirement can change with time, due to carbon buildup, which changes the compression ratio. If your van's engine knocks, pings or runs on, switch to a higher grade of fuel (if possible) and check the ignition timing. Sometimes changing brands of gasoline will cure the problem. If it is necessary to retard the timing from specifications, don't change it more than a 2 degrees. Retarded timing will reduce the power output and the fuel mileage, plus it will increase the engine temperature.
The vehicles covered by this guide are capable of running on various types of blended gasolines as well. Blended gas containing any ONE of the following blends are allowed if they contain no more than 15 percent MTBE (Methyl Tertiary-Butyl Ether), 10 percent Ethanol (Ethyl or grain alcohol) or 5 percent Methanol (wood alcohol).
See Figures 1 and 2
Use ONLY SG/CC, SG/CD, SH/CC or SH/CD rated oils of the recommended viscosity. Under the classification system developed by the American Petroleum Institute (API), the SH rating (or latest superceding alpha-rating) designates the highest quality oil for use in passenger vehicles. In addition, Chevrolet recommends the use of an SH/Energy Conserving oil. Oils labeled Energy Conserving (or Saving), Fuel (Gas or Gasoline) Saving, etc. are recommended due to their superior lubricating qualities (less friction-easier engine operation) and fuel saving characteristics. Pick your oil viscosity with regard to the anticipated temperatures during the period before your next oil change. Using the accompanying chart, choose the oil viscosity for the lowest expected temperature. You will be assured of easy cold starting and sufficient engine protection.
For the first few years of production (1985-88) GM's preferred recommendation was the use of 10W-30 in the 4.3L engine, but only if ambient temperatures did not drop below 0°F (-18°C). During these years 5W-30 was recommended for use, but only in ambient temperatures below 60°F (16°C). It does not seem like any significant changes were made to the bottom end of this engine, but for 1989 and later models, the recommendations changed to prefer 5W-30 for all ambient temperatures.
The mileage figures given in your owner's manual are the Chevrolet recommended intervals for oil and filter changes assuming average driving. If your Astro or Safari Van is being used under dusty, polluted or off-road conditions, change the oil and filter sooner than specified. The same thing goes for vehicles driven in stop-and-go traffic, used for only for short distances or used in heavy hauling such as trailering or filled with passengers and luggage.
Always drain the oil after the engine has been running long enough to bring it to operating temperature. Hot oil will flow easier and more contaminants will be removed along with the oil than if it were drained cold. You will need a large capacity drain pan, which you can purchase at any store that sells automotive parts. Another necessity is a container for the used oil. You will find that plastic bottles, such as those used for bleach or fabric softener, make excellent storage jugs.
Dispose of used oil ONLY by finding a service station or facility which accepts used oil for recycling.
Although GM recommends changing both the oil and filter during the first oil change, they then usually permit that the filter be replaced only every other oil change thereafter. For the small price of an oil filter, its cheap insurance to replace the filter at every oil change. It is recommended that you change both the oil and filter together at each service. One of the larger filter manufacturers points out in it's advertisements that not changing the filter leaves 1 quart of dirty oil in the engine. This claim is true and should be kept in mind when changing your oil.Synthetic Oils
There are excellent synthetic and fuel-efficient oils available that, under the right circumstances, can help provide better fuel mileage and better engine protection. However, these advantages come at a price, which can be 3 or 4 times the cost per quart of conventional motor oils.
Before pouring any synthetic oils into your vehicle's engine, you should consider the condition of the engine and the type of driving you do. Also, check the manufacturer's warranty conditions regarding the use of synthetics.
Generally, it is best to avoid the use of synthetic oil in both brand new and older, high mileage engines. New engines require a proper break-in, and the synthetics are so slippery that they can prevent this. Most manufacturers recommend that you wait at least 5000 miles (8000 km) before switching to a synthetic oil. Conversely, older engines are looser and tend to loose more oil. Synthetics will slip past worn parts more readily than regular oil. If your van already leaks oil (due to bad seals or gaskets), it will probably leak more with a slippery synthetic inside.
Consider your type of driving. If most of your accumulated mileage is on the highway at higher, steadier speeds, a synthetic oil will reduce friction and probably help deliver fuel mileage. Under such ideal highway conditions, the oil change interval can be extended, as long as the oil filter will operate effectively for the extended life of the oil. If the filter can't do its job for this extended period, dirt and sludge will build up in your engine's crankcase, sump, oil pump and lines, no matter what type of oil is used. If using synthetic oil in this manner, you should continue to change the oil filter at the recommended intervals.
Vans used under harder, stop-and-go, short hop circumstances should always be serviced more frequently, and for these trucks, synthetic oil may not be a wise investment. Because of the necessary shorter change interval needed for this type of driving, you cannot take advantage of the long recommended change interval of most synthetic oils.