Engine pre-oiling: A critical procedure for any fresh engine

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Engine pre-oiling: A critical procedure for any fresh engine

A customer’s engine represents a major investment. Regardless of whether the engine is new (a factory replacement engine), a freshly rebuilt engine, or an engine that has been stored for an extended period, it can be quickly damaged if the bearings and friction related components are not properly lubricated prior to firing the engine for the first time.

NEVER start a fresh engine without first circulating oil through the oil galleys to provide oil to the bearings and valvetrain.

Even though the engine may have been recently assembled with a quality engine assembly lube on the bearings, pre-oiling is absolutely mandatory. Rather than cranking the engine and waiting for oil pressure to build via the engine’s oil pump, pressurizing the oil circuits before ever cranking the engine will ensure lubrication that will protect the bearings and valvetrain from damage during the first rotation of the crank.

This also holds true for even a previously run engine that may have sat dormant for a long period of time. Main bearing, rod bearing, cam bearing, rocker tip and other potential valvetrain damage can be easily avoided by first pressure pre-oiling the engine before it’s started.

As we all know, engines that feature an oil pump driven by the camshaft can be pre-oiled by removing the distributor and running the oil pump with the use of an adapter and a power drill. That traditional practice works fine, assuming that you’re able to drive the oil pump without rotating the crankshaft. However, late model engines that feature a front-mounted oil pump that’s driven by the crankshaft cannot be pre-oiled in this manner. The use of a pressurized pre-oiling tank allows you to easily push pressurized oil throughout the engine’s oil circuit without the need to turn the engine’s oil pump (the LS engine is but one example). These pressure tanks are applicable to any engine, regardless of the year of manufacture or the location and design of the oil pump.

It’s all too common for some folks to assume that there’s no need to pre-oil, since they believe that the engine’s oil pump will distribute oil through the engine’s oil circuit quickly enough to protect the bearings. A common practice involves disconnecting the coil wire and cranking the engine, in order for the oil pump to build pressure. While this will eventually pull oil from the sump and deliver to the main feeds, in the process of cranking the engine (even without firing), there is no guarantee that you’ll have adequate lubrication delivered quickly enough to protect the bearings during this initial cranking period. Beyond a concern for sending oil to the main bearings, by cranking the engine, it will take even longer to send oil all the way up to the rockers.


It’s important to understand that you never want to allow the crankshaft main journals, rod journals or cam journals to ride directly on the bearing surfaces. An oil film is needed to support the journals. With oil already present (by pressurizing the system), as soon as the crank begins to rotate, this oil film will create a ramp that will support the journals.

Engine main, rod and cam bearings can be damaged in the blink of an eye if oil isn’t delivered quickly. Just because you topped off the oil pan sump and perhaps added some oil into the oil pump during assembly, this is no guarantee that oil will be delivered to the bearings quickly enough to avoid damage. To protect the engine, pre-oil it first by pressurizing the system.

If you crank and start the engine without lubrication already delivered, you will end up with damaged bearings and/or valvetrain pieces.

Pre-oiler tanks

An engine pre-oiler tank works on a very simple principle. The tank is designed as a simple pressure tank. Oil is added to the tank reservoir.

When charged with compressed air and the tank’s valve is open, pressurized oil is forced into the engine via a connection hose between the tank and engine block.

This is the easiest and by far the most efficient method of pressurizing the engine’s oil circuits, without the need to use an oil pump drive adapter and a hefty power drill (and as mentioned earlier, with late model crank-driven oil pump designs, you can’t turn the oil pump with a drill anyway).

An engine pre-oiler can be used whether the engine is on a stand, on an engine dyno or with the engine already installed in the vehicle.

Note that pre-oiler tanks are available in both steel and aluminum construction. Steel tanks are essentially the same type as used for propane. If not stored properly with clean oil, it is possible for rust to form inside the tank which can lead to potential oil contamination. Steel or aluminum tanks will do the job, but aluminum tanks eliminate this concern.

How to use a pre-oiler tank

Locate an accessible oil port on the engine block (the port to be used for the oil pressure sender is an ideal location). Remove the oil pressure sender or threaded plug from that port.

Locate the proper fitting to adapt the pressure oiling tank’s hose fitting to the port (for example, 1/4-inch NPT, 1/8-inch NPT, etc.). Hoses provided with these tanks are generally about eight feet long, allowing you to place the tank securely on the shop floor. Remove the oil reservoir cap from the tank and add fresh, clean engine oil to the tank’s oil reservoir. Depending on the make/model of the pressure oiler, capacity can range from four to 12 quarts (generally, a minimum of about a three-quart tank capacity will be enough to provide sufficient pre-oiling). Install the oil reservoir’s cap. Make sure that the pressure oil tank’s flow control valve is in the closed position.

Connect the tank’s hose to the engine block. Make sure that the connection is secure (while not mandatory, a bit of Teflon sealant paste on the adapter threads may be a good idea to prevent potential leakage. Do not use Teflon tape, as loose “threads” of Teflon tape can potentially break loose and enter the system!).

Remove the engine’s valve covers in order to be able to visually confirm oil delivery to the rockers. If the engine is in the vehicle, place a fender cover or soft towel on the front fender (protecting painted surfaces from the pressure oiler’s delivery hose). Cover exhaust manifolds/headers with clean towels, in case oil dribbles from the top of the heads.

Connect the pressure oiler to your shop’s air compressor. Open the pressure oiler’s flow control valve to introduce oil into the engine. You’ll hear oil gurgling inside the engine as it is pushed through the block’s oil passages. You should see oil delivered to the valvetrain.

Verify that all rocker locations are receiving oil. In some cases, you’ll only need to apply this pressure for perhaps as little as five to 10 seconds (chances are, providing there are no restrictions in the engine’s oil circuit, bearings and other wear-related surfaces will likely be lubed in as little as five seconds or so, but some V engine designs may require a longer period for oil to flow to the rockers on both banks).


Using a drill

If the engine is outfitted with an oil pump that is mechanically driven by a shaft that is connected to a distributor (granted, uncommon on late model engines), remove the distributor and the intermediate oil pump drive shaft. Insert an extended priming shaft of the style that will engage the oil pump’s shaft (these are available in hex or slotted styles to accommodate various designs of GM, Ford, Chrysler, etc.). Install an oil pressure gauge to the engine block. Remove the valve cover(s). Connect a power drill to the priming shaft and drive the pump until the gauge shows that oil pressure is established. Continue to turn the pump while monitoring the rocker arms. Keep turning the pump until you see oil exiting at the rockers (on both banks if dealing with a V type engine). Once oil is being delivered to the rockers, and if you’ve achieved at least minimum oil pressure on the gauge, oil has been delivered throughout the engine. By the way, don’t try this with a cordless drill or a low-powered electric drill. Use a strong electric or pneumatic drill.

TIP: While pressurized oil is being forced through the engine, it’s a good idea to slowly manually rotate the crankshaft a full 360 degrees using a wrench at the crankshaft snout (with spark plugs removed for easier crank rotation). This provides added insurance that the oil feed holes on the crank get a healthy shot of oil from the bearing saddle oil holes as the oil transfer holes between bearings and journals align.

Close the flow control valve on the pressure oiler and disconnect the compressed air line. Carefully remove the pressure oiler’s hose from the engine block (place a rag under the end of the hose to prevent dripping oil onto surfaces as the hose is removed). Reinstall the vehicle’s oil pressure sender to the engine block.

Check engine oil level in the engine’s oil pan sump (check the dipstick). If you’ve introduced the type and grade of oil that will be routinely used, check the dipstick and add to the fill mark if necessary. If overfull, drain oil from the sump and adjust the oil level.

NOTE: The type of oil to use during pre-oiling should be the same type and viscosity that will be initially run in the engine. If the engine is newly built, avoid using a synthetic oil for break-in, as this may prevent the piston rings from properly bedding against the cylinder walls. Ideally, it’s best to use a dedicated break-in oil for initial firing (an oil designed with the appropriate level of zinc phosphate). If you’re running a flat tappet camshaft (solid or hydraulic), you must run an oil with adequate high-pressure lubricant (commonly referred to as zinc phosphate). Specialty engine oils are readily available today that are specifically designed to provide the needed protection for flat tappet lifters/camshafts. If you’re running a performance roller cam coupled with high valve spring pressure, be aware that higher valve spring pressures can promote wear on rocker and valve tips, so a specially formulated oil (or concentrated zinc additive added to your oil of choice) is highly recommended. Most of today’s off-the-shelf engine oils feature greatly reduced levels of high pressure zinc additives, so it’s important to select an oil that retains a high level of zinc. These specialty oils are now readily available from firms such as Brad Penn, Joe Gibbs, Lucas, Royal Purple, Comp Cams and others. If the engine is a non-altered production type with a roller cam, these specialty oils won’t be necessary.

In order to “break in” the engine, follow the recommended procedure when dealing with a flat tappet camshaft (fire the engine, do not allow it to idle, run at approximately 2,400 rpm, for about 15 minutes, varying engine speed during the break-in period). Even if you’re running a roller cam, run the engine at varying speeds for a few minutes to allow the rings to seat.

Naturally, monitor engine oil pressure and temperature during the break-in period. When breaking-in a flat tappet cam, it’s important that the engine is not stopped at any point during the procedure. That’s why it’s important to perform a solid pre-flight check to verify that you have no leaks, timing is correct (or as close as possible), etc., before you start the engine. And make sure that the fuel tank has an adequate supply to avoid stopping the engine prematurely.

Once the initial break-in has been accomplished, change the engine oil and filter. Do not immediately pitch the used oil filter. On a workbench, cut the filter apart (dedicated oil filter cutters are available), remove the filter element, and inspect all filter surfaces/pleats. Any large pieces of metal debris found in the filter is cause for alarm (bearing damage, etc.).

Remember, the need for pre-oiling is not limited to only performance engines. Any fresh engine (or one that has been dormant for an extended period) should be pre-oiled prior to its initial starting.   ●



(The following pre-oiler tanks feature an oil reservoir. They are operated with shop compressed air.)


156 Galewski Dr.

Winona, MN 55987

(800) 533-8010



12 quart capacity

Lightweight aluminum construction (eliminates potential rust inside the tank)

Eight foot 1/4-inch hose with swivel end

Pop-off safety valve

Pressure gauge

Two standard fittings and one LS fitting



P.O. Box 1188

Jackson, MI 49204

(517) 787-8172



Four quart capacity


Steel construction

Optional oil pressure gauge

Eight foot hose



(800) 521-2936



Five quart capacity


Steel construction

Eight foot hose

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