Priming gerotor pumps can be an ordeal. We’ve run into a couple of older LS engines that have sat for a very long time and it’s not uncommon for these engines to fail to make oil pressure. This occurs because LS engines mount the gerotor oil pump directly over the crankshaft snout on the front of the engine. Compounding this problem is a long tubular pickup that extends to the rear of the engine oil pan, creating a long, circuitous route from which the pump must “pull” oil. GM’s suggestion for new crate engines with a full level of oil in the pan is to remove all eight spark plugs and spin the engine over with the starter motor. Unfortunately, this trick often does not create oil pressure.

What is required is that the oil pump is primed. Melling suggests this technique that will almost always achieve success. On most Gen-III and Gen-IV LS engines, there is a main oil galley plug at the front of the block alongside the front timing chain cover. Remove this plug with an 8mm Allen wrench to allow access to the galley. Now insert a roughly 2-foot length of 3/8-inch rubber fuel hose into the galley port and connect a small funnel to the other end of the hose and pour five to six ounces of engine oil into the hose. This will prime the oil pump.

By removing the oil pressure galley plug from the front driver side of the LS block and using a 3/8-inch length of rubber hose and a small funnel to pour about 5-6 ounces of oil into the oil pump, the pump will be primed. This will make it more likely to create oil pressure when spinning the engine with the starter motor.

Now remove the rubber hose and replace the oil galley plug. With the spark plugs removed, this should allow the starter motor to spin the engine over with sufficient speed to allow the oil pump to create pressure. With oil pressure, it’s now safe to start the engine. If the engine still does not make oil pressure, this will require engine disassembly to uncover the problem. We should not have to tell you not to run the engine without oil pressure.

If gravity-priming the oil pump doesn’t net you oil pressure, another method is to use an external tank, pressurized by shop air, to prime the entire oil system.

Under Pressure

With a freshly rebuilt engine, it’s a really good idea to pressure lube the engine with a dedicated pressure device. Summit sells an inexpensive pressurized container (P/N SUM-CSUM-9166) that can be filled with enough oil to pressure lube the engine before starting. Melling also sells a very nice pressure lubing tank (PN MPL-201). If you feel adventuresome, you can make your own oil pressure pre-luber for much less money using a 2-1/2-gallon plastic bucket and lid fitted with a small-block Chevy oil pump bolted to the lid. Extend the pickup to the bottom with 5/8-inch rubber hose and add a pressure outlet fitting from the pump to allow connecting to the same pressure port in the block.

Then you can spin the oil pump with a small-block oil pump drive shaft and a 1/2-inch drill motor. This will pump pressurized oil to the mains, rods, and lifters and completely pre-lube the engine with fresh oil. We also included a drain-back feature on our kit to allow oil from the drain plug hole back to the bucket. Whether you buy one or build one, priming the oiling system on an engine with a Gerotor pump doesn’t have to be a difficult process.

We built our own LS engine oil pre-luber using a 2-1/2-gallon bucket, a thin aluminum plate to reinforce the lid, and we bolted a small-block Chevy oil pump to the lid. We used a couple of AN fitting adapters and a 1/2-inch drill motor to spin the oil pump and make oil pressure. We even have a drain-back feature from the oil pan drain plug back to the tank.