How to Prime a Dry Sump Oil System

Fill the tank and filters with the correct oil, wet the pump and pressure-side lines with oil, then build pressure using a pre-oiler or by cranking the engine with ignition/fuel disabled until you see stable oil pressure and a steady return flow to the tank; check for leaks, top off, and verify on first start. Priming prevents a dry start, avoids air-lock in the pressure stage, and ensures the scavenge sections return oil cleanly to the tank. The exact steps vary by pump and engine, but the core goals are identical: get oil into the pump, galleries, filters, cooler, and lines before the engine fires.

Why priming a dry sump system matters

Unlike a wet sump, a dry sump stores oil in a separate tank and relies on multiple pump stages: one to pressure-feed the engine and others to scavenge oil back to the tank. Air in the pressure stage or suction leaks on the tank-to-pump feed line can prevent oil pressure from building, risking immediate engine damage. A proper prime removes air, confirms correct pump rotation and plumbing, and establishes oil pressure and return flow before combustion loads the bearings.

What you’ll need

Gather the following tools and supplies so you can prime efficiently and safely without introducing contaminants or air leaks.

• Correct oil type and quantity for your engine and tank (account for lines, cooler, and filter volume)
• Fresh filters (remote pressure filter and any scavenge screens/filters)
• AN wrenches, torque specs, and new O-rings/seals for fittings as needed
• External pre-oiler/pressure canister (2–3 qt/L) or a suitable priming rig; alternatively a strong battery for cranking
• Oil pressure gauge or data system that reads during cranking
• Catch pan, rags, safety glasses, gloves
• Optional: low-speed drill/driver and proper mandrel for pump shaft (only if the pump is designed for external spinning), infrared thermometer, thread sealant compatible with oil (no PTFE tape on AN flare seats)

Having the right tools reduces the risk of dry running the pump, over-cranking the starter, or contaminating the oil circuit during fitting adjustments.

Preparation and inspection

Before you attempt to build pressure, confirm the system is assembled correctly and already “wet” where it can be.

1. Review the manufacturer’s plumbing diagram and rotation arrow for your specific pump (Aviaid, Dailey, ARE, Moroso, Peterson, etc.). Verify belt alignment and tension.
2. Confirm check-valve orientation (tank vent, pressure-side anti-drainback, and any cooler bypass). A backwards check valve will block flow.
3. Remove and clean scavenge pickup screens. Reinstall per spec.
4. Pre-fill the remote pressure filter with clean oil; install and torque. If mounted horizontally, fill and cap, then install promptly.
5. Backfill the oil cooler and pressure-side lines (from filter outlet toward engine) with oil to minimize air pockets.
6. Fill the tank to the manufacturer’s cold level (often mid-stick with engine off). Do not top off; the level will drop as lines fill.
7. Wet the pump: pour oil into the pressure-stage inlet hose/fitting and slowly rotate the pump or crankshaft by hand in the correct direction to draw oil into the rotors/gears.
8. Charge the battery and connect a reliable ground. Disable ignition and fuel (pull fuses, coils, injectors, or use a kill switch). Removing spark plugs reduces cranking load and speeds priming.
9. Position the vehicle level and ensure the tank is mounted per spec (feed at bottom, vent at top, minimal height above pump to reduce suction head loss).

These steps reduce the amount of air the pump must clear, shorten priming time, and protect both the pump and bearings during initial rotation.

Priming methods

Method 1 — External pre-oiler (preferred)

This method pushes clean oil under moderate pressure into the engine’s main gallery so the oil pump, bearings, and lifters are wet before any cranking. It’s the safest approach for fresh builds and race engines.

1. Identify a suitable gallery port: common points include the pressure sensor port, a plug near the main oil gallery, or ports on a remote filter head. Remove the plug/sender and fit the pre-oiler hose.
2. Fill the pre-oiler with the same oil you will run. Pressurize to about 20–40 psi (1.4–2.8 bar) per the device instructions.
3. Open the pre-oiler valve and feed oil into the engine. Slowly rotate the crank by hand or bump the starter (ignition/fuel disabled) to index oil passages.
4. Watch the oil pressure gauge and look for return flow into the tank. Bubbles should diminish as galleries fill and scavenge stages begin to move oil back.
5. Continue until pressure stabilizes and you see a steady, mostly bubble-free return stream into the tank. Close the valve and depressurize the pre-oiler.
6. Top the tank back to the cold mark and reinstall the gallery plug/sensor with the correct sealant or crush washer.
7. Inspect for leaks at all AN fittings, filter heads, the pump, and the tank.

By backfilling the engine and pump, this approach minimizes dry contact in the pressure stage and shortens the time to a stable return stream.

Method 2 — Cranking the engine (common and effective)

Cranking turns the belt-driven pump at low speed while you monitor pressure and return. It works well if you have pre-filled the tank, filter, and lines.

1. Confirm ignition and fuel are disabled and plugs are removed (if practical).
2. Crank in 10–15 second bursts with 30–60 seconds of rest to protect the starter. Watch the pressure gauge.
3. Within 10–30 seconds of total cranking time, you should see pressure build (often 20–40 psi during cranking on many engines) and a visible return stream into the tank.
4. Once pressure and steady return are achieved, stop cranking and recheck the tank level. Top to the recommended cold mark.
5. If no pressure appears after ~30 seconds total, stop and troubleshoot before proceeding.

This method is simple and avoids special tools, but it depends on your prep work to ensure the pump isn’t running dry for long.

Method 3 — Spinning the external pump (only if designed for it)

Some pumps can be spun directly at low speed with a drill/driver and proper adapter, or by turning the pump pulley by hand. Do not attempt this unless the manufacturer permits external spinning and you can control speed.

1. Disconnect the belt if required and attach the approved drive adapter to the pump shaft. Verify rotation direction.
2. Spin the pump slowly (a few hundred rpm), watching the gauge and the return to the tank.
3. As pressure builds and the return stream steadies, stop and reassemble the belt drive to spec.
4. Recheck tank level and fitting torque.

This technique primes the system without cranking the engine, but improper tooling or overspeeding a dry pump can cause immediate damage.

Bleeding air and verifying the system

Even after pressure appears, small air pockets can persist in high points and coolers. Bleeding ensures rapid, stable pressure on first fire.

• Crack the highest pressure-side fitting (e.g., at the filter outlet or gallery adapter) just enough to vent air as oil seeps, then retighten to spec.
• Backfill the oil cooler and remote lines during prep; verify flow direction so the internal bypass (if present) works correctly.
• Observe the tank return: foam should diminish quickly. Persistent foam suggests suction leaks or high aeration in the scavenge sections.
• Set final oil level hot: after the first full-heat run, check the level at idle per the tank manufacturer’s instruction and mark the dipstick.
• Confirm tank vent routing is clear and not submerged; a restricted vent can cause aeration and pressure fluctuations.

Proper bleeding leads to quicker pressure rise on startup, less aeration, and more consistent readings across temperature ranges.

First start and follow-up checks

With pressure verified during priming, the first start confirms system stability under combustion loads and heat.

1. Reinstall spark plugs, restore ignition and fuel, and confirm timing/base maps are safe for initial fire.
2. Start and hold 1,500–2,000 rpm for 60–90 seconds while monitoring oil pressure, return flow, and leaks. Expect 40–70 psi hot at moderate rpm on many builds (follow your engine’s spec).
3. Shut down, inspect every fitting and the pump/tank seams, and re-torque where required.
4. With oil hot, set the correct tank level at idle and mark the dipstick. Note that level will be lower than cold due to oil in lines and cooler.
5. Log pressure vs. rpm and temperature; unusual fluctuations can indicate foaming, relief valve issues, or suction leaks.
6. After initial run-in, change oil and filters to remove assembly debris and sealant crumbs.

These checks validate priming success and establish a baseline for pressure behavior that you can monitor over time.

Troubleshooting: no pressure or no return

If pressure fails to build or the return stays foamy, stop and resolve the root cause before trying again.

• Incorrect pump rotation or misrouted lines (verify with the manufacturer’s schematic).
• Suction leak on the tank-to-pump feed hose (loose AN nut, nicked O-ring, porous hose, sharp bend causing cavitation).
• Blocked pickup or tank feed, clogged scavenge screens, or collapsed filter media.
• Pressure relief valve stuck open or set too low; inspect and clean.
• Backwards or stuck check valve in the pressure line, cooler circuit, or tank vent.
• Cooler blockage; temporarily bypass to test.
• Oil too viscous in cold conditions; warm the oil/tank or use the correct grade for ambient temperature.
• Pump wear or incorrect end-clearance from prior scuffing; rebuild or replace as needed.
• Air trapped in high points; crack a pressure-side fitting to purge, then re-prime.

Systematic checks usually reveal a simple assembly or plumbing error; correcting it before running saves the pump and bearings.

Safety and best practices

Dry-sump systems operate under pressure and can move large volumes of oil quickly. Treat priming like a critical maintenance procedure.

• Wear eye protection; high-mounted lines can spit when bleeding.
• Use proper AN fittings and hose rated for oil and temperature; avoid PTFE tape on flare fittings and keep sealants out of the flow path.
• Never cap the tank vent when running; pressure can build rapidly and cause leaks or tank damage.
• Avoid extended dry cranking; limit bursts and allow the starter to cool.
• Document hose routing and fitting torque; label lines to prevent cross-connection after service.

Following these best practices reduces the risk of leaks, fires, and component damage during and after priming.

Summary

To prime a dry sump oil system, wet the pump, pre-fill the tank, filters, cooler, and pressure-side lines, then build pressure either with an external pre-oiler or by cranking with ignition/fuel disabled until you see stable gauge pressure and a steady, bubble-free return to the tank. Verify fittings and rotation, bleed trapped air at high points, top the tank to the correct level, and monitor closely on first start. Careful priming protects the pump and bearings and sets the system up for reliable pressure and clean oil return under load.

How to prime a sump pump for the first time?

Turn on the water and wait Fill water into the pump body and suction pipe slowly, to allow for air to escape as the priming water fills up to the top of the pump body. Once water flows from the opposite end of the hose, turn off the water.

What is the preferred method of priming an engine lubrication system with engine oil?

Prime the system by turning the oil pump with a power drill and Priming Tool, or with an external Engine Preluber. Rotate the crankshaft by hand, while priming the system. This ensures that oil gets around all the bearings and into all the internal oil passages.

How to prime an oil pump for the first time?

Counterclockwise. So we want to of course drive the pump. Counterclockwise. As well we grab our drill setup.

What are the common problems with dry sump?

Low oil pressure readings or warnings. Unexplained oil consumption. Oil leaks near the reservoir or hoses. Sludge or debris in the oil tank.