The oil pump for your Chevy Astro van is located on the part of engine block that is covered by the oil drain pan. If you have a bad pump that needs to be changed, it will require removing the drain pan to reach it. This will be a time consuming process of multiple hours, and should only be attempted by someone with extensive knowledge of their van and experience with engine maintenance.
Raise the van and support it on jack stands. Drain the oil into a container by removing the pan's drain plug. If the vehicle is close to its regular oil change, remove the oil filter also. Disconnect the negative battery cable.
Disconnect the exhaust pipe at the exhaust manifold and tie the system aside. Remove the starter by removing any starter braces or shields under the van, labeling the wires and removing them from the starter solenoid, removing the two mounting bolts and lowering the starter from the engine.
Detach the oil pan from the van by removing its bolts. Dislodge the pan from the block with a hammer and a block of wood if it is stuck. Don't pry between the pan and block, or you could damage the sealing surfaces.
Remove the mounting bolts on the oil pump's flange, along with the bracket nut for the pick-up tube. Remove the pump and pick-up assembly.
Install the new oil pump by turning the shaft so the gear tang connects to the slot on the pump driveshaft's lower end. The pump will slide over the pump driveshaft's lower bushing. Connect and tighten the mounting bolts to the pump and the bracket nut to the tube.
Clean the mating surfaces on the block and the oil pan, and carefully scrape away all traces of sealant from the pan and block. Apply new RTV sealant to the oil pan flange and the engine block.
Reconnect the oil pan, along with the starter and exhaust pipe. Add fresh oil to the van and install a new oil filter if needed. Reconnect the battery cable, start the engine and check for any leaks around the oil pan.
