How to prime an oil pump on a Subaru?

Priming an oil pump on a Subaru means filling the pump and its passages with oil and spinning the engine with ignition disabled until oil pressure is confirmed. The goal is to prevent a dry start after pump work or replacement. In most cases, you pre-fill the pump and rotate the crank until oil pressure appears on a gauge or the warning light goes out, then start the engine and monitor pressure closely.

The following guide covers the typical approach used on Subaru flat-four engines (including EJ, FA, and FB series). Procedures can vary by model year and specific engine design, so always consult the official service manual for your car and consider professional help if you’re unsure.

What you’ll need

The list below outlines common tools, supplies, and safety considerations to prepare for priming the oil pump.

• Engine oil of the correct specification (same viscosity as your owner's manual recommends, typically 0W-20 or 5W-30 for many Subarus).


• New oil filter (if you’re performing pump work as part of an overall oil system service).


• New pump O-rings or gaskets as specified by the replacement pump kit.


• Shop towels and a drain pan for any minor oil spills during the procedure.


• A means to disable the fuel system and ignition (pull the fuel pump fuse/relay and/or disconnect ignition coils or the ECU power, depending on your model).


• A socket/ratchet or breaker bar for turning the crankshaft pulley bolt, plus a suitable crank access tool if required by your engine layout.


• Spark plug removal tool or socket to remove all spark plugs (optional but recommended to ease cranking).


• A clean, visible oil pressure gauge (or a test light) to monitor oil pressure during priming, if available.

With these items, you’ll be prepared to prime the pump and verify oil pressure before starting the engine. Having the right tools helps reduce the risk of premature wear and makes the process safer and more predictable.

Step-by-step priming procedure

These steps describe the typical process used when priming an oil pump on a Subaru. Model-specific details may vary, so adapt as needed and follow your manual.

1. Park the vehicle on a level surface, engage the parking brake, and disconnect the battery or ensure the ignition is off if you’re working near electrical systems.


2. If possible, pre-fill the new oil pump with clean engine oil and lubricate its internal gears or surfaces as recommended by the pump manufacturer.


3. Disable the fuel system and ignition to prevent accidental starting. Remove the fuse/relay for the fuel pump and, if advisable, disconnect the ignition coils or ECU power so cranking won’t start the engine.


4. Remove spark plugs from all cylinders to reduce compression and make it easier to crank the engine during priming.


5. Crank the engine slowly using a ratchet on the crankshaft pulley bolt (clockwise rotation). Do short cranks (about 10–15 seconds each) and pause for 10–15 seconds between cycles to avoid overheating the starter. Repeat several times to draw oil through the pump and into the galleries.


6. Observe oil pressure behavior with a gauge if you have one, or watch for the oil pressure warning light to go out. If you see pressure within the expected range (even a low reading is better than a cold dry start), continue cranking briefly to circulate oil.


7. Reinstall the spark plugs, reconnect the ignition and fuel systems, check the oil level one more time, and attempt a cautious start. Once the engine starts, monitor oil pressure closely and listen for any knocking or unusual noise. If pressure does not come up quickly, shut down and recheck the pump seating, oil level, and connections.

Following these steps helps ensure the oil pump is primed and ready to circulate lubrication before full engine operation. Avoid extended cranking without oil pressure, as it can damage the starter and other components.

Engine variations and caveats

The general priming approach works across Subaru engines, including EJ (older flat-four) and newer FA/FB designs. Some model years may have different access points to the pump or unique surge paths, soalways refer to your service manual for torque specs, oil pressure ranges, and any model-specific cautions.

What to check if priming fails

If oil pressure does not register after priming, inspect these points to identify common issues that can prevent a successful prime.

• Ensure the oil level is correct and that you are using the correct viscosity for the engine and climate.


• Verify the oil pump is installed correctly, seated fully, and that the drive gear or chain is properly aligned with the crank and cam gears.


• Check for debris or a clogged oil pickup screen that could restrict oil flow to the pump.


• Inspect the seals, gaskets, and O-rings on the pump for leaks or improper sealing.


• Verify the oil pressure sensor and gauge are functioning; a faulty sensor can mislead you about actual pressure.

If you’re unsure about the pump installation or cannot achieve oil pressure after repeated attempts, stop and consult a qualified mechanic. Incorrect priming can cause insufficient lubrication and severe engine damage.

Summary

Priming an oil pump on a Subaru centers on pre-filling the pump, disabling fuel and ignition to avoid accidental starting, cranking the engine with spark plugs removed to fill oil passages, and verifying oil pressure before a full startup. While the core technique remains consistent across EJ, FA, and FB engines, always follow your specific model year manual for precise steps, torque values, and safety precautions. When in doubt, seek professional assistance to prevent costly engine damage.

How do you manually prime an oil pump?

To manually prime an oil pump, first, install it on the engine, fill the oil filter, and remove the oil gallery plug(s) to access the oil passages. Then, use a priming tool or a modified distributor to spin the oil pump and force oil through the system. The process is complete when you see oil reaching the rocker arms at the top of the engine. 
This video demonstrates how to prime an oil pump using a modified distributor: 1mMelling Engine PartsYouTube · Jan 28, 2011
Step 1: Prepare the system

• Pour oil into the oil pan and fill the oil filter before installing it on the engine. 
• Remove the oil gallery plug on the engine block to allow oil to enter the system. 
• Remove the valve covers to allow you to monitor oil flow to the rocker arms later. 

Step 2: Prime the pump

• Insert a priming tool or a modified distributor (with the gear removed) into the distributor hole to engage the oil pump shaft. 
• Use a power drill or a speed handle to slowly turn the tool. You should feel resistance increase as the pump fills with oil. 
• Continue turning until oil begins to flow from all the push rods at the top of the engine, confirming the system is full. 

This video shows how to use an LS engine specific priming tool: 1mScantron's GarageYouTube · Sep 8, 2023
Step 3: Finalize the process

• Once oil is visible at the rocker arms, rotate the engine manually a few times to ensure all lifters are oiled properly. 
• Reinstall the oil gallery plug and the valve covers. 
• Install an oil pressure gauge to monitor pressure during the first start-up. 

You can watch this video to see how to monitor oil pressure with a gauge: 1mMelling Engine PartsYouTube · Jun 8, 2016

How to check if an oil pump is primed?

It's easy to check; just unscrew the filter and see if there's any oil in it. If you have oil flow at the rocker spindles, then the pump has already primed itself and is pumping oil. Check the oil level in the sump by removing the plug in the bottom of the case and see how much drains out.

How to make sure an oil pump is working?

Recognizing the Signs of a Bad Pump

1. See if the oil pressure light is lit on your vehicle's dashboard.
2. Look at the engine temperature gauge to see if your engine's overheating.
3. Listen for whining or clinking noises from your engine while it's running.

Do you need to prime an oil pump?

Priming your oil pump and your engine before start up of a new engine is very important. No new engine should be started up dry, but it is often difficult on new engines with a front crank driven oil pumps to prime.