How to Run a Boat Motor Out of Water: 15 Steps (with Pictures)

Flushing a boat motor by running it out of water is a routine maintenance task. Some newer motors have built-in attachments that accept a hose nozzle. This article was co-authored by our trained team of editors and researchers who validated it for accuracy and comprehensiveness. Together, they cited information from 18 references. Boat Motors and Marine Engines. Read your manual before starting the motor out of water. Check the manual to find out where your intakes are located and whether they have built-in attachments for a garden hose.

However, you should still check the specific procedure for your model. Screw the hose directly into the motor if it has a built-in attachment. With the engine lowered into the vertical position not tilted in the tow position , locate the water intakes on the sides of the lower unit. Screw the hose nozzle into one of the intakes. Your manual will most likely recommend covering the other intake with heavy tape. Purchase motor muffs at a boating store or online.

They look like earmuffs connected by a long, V-shaped rod. Wet the muffs to get a better seal. Many boat owners like to splash the insides of the muffs with water before attaching them to the motor. Clamp the muffs to the motor and stay clear of the propeller. Be sure to position the muffs so the connecting rod is located in front of the motor on the opposite side of the propeller. Injury or damage will result if the engine accidentally slips into gear and the connecting rod is on the propeller side of the motor.

Screw the garden hose onto the muffs. One of the muffs has a nozzle, and the other is solid. Find the one with the nozzle, then screw your garden hose into it.


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Turn on the water. After attaching the garden hose, head to the faucet and turn on the water. Check your manual to see if it specifies a water pressure setting.

Why Flush?

Many manufacturers recommend setting it to about half pressure. Put the engine in neutral. Make sure the gearshift or throttle is in the neutral position. The engine needs to be in neutral to start and should stay in neutral while you run it.

Ear Muffs or Hose hook-up ???

As with other flushing devices, caution must be exercised:. Most outboard manufacturers' flushing recommendations are similar. All of them make a statement about ensuring that all water is drained from the engine after flushing. This is especially important in freezing climates, so that there is no water left inside the engine that could then freeze, and cause damage. However, there are some differences, so here they are, straight from the manufacturers themselves:. For flush-muff attachments, temporarily cover the auxiliary water inlets with heavy tape on their to hp models and high-performance Lightning M2-type gear cases remember to remove the tape afterward.

Water pressure should be between 20 and 40 psi. You can buy a pressure gauge attachment at a hardware store to monitor psi. Flush for at least five minutes at an idle speed, with the engine in a vertical position. When using the flushing port, it is not necessary to run the engine.

How to Properly Test Your Outboard At Home

Keep the engine vertical after flushing so that all water drains from the powerhead. Honda's flushing procedure varies by engine size and model. In all cases, the engine must be in the vertical position during flushing and after, to drain the water from the engine.

Smaller engines 2 to 20 hp: Flushing in a small container such as a flushing bag, small bucket, or can is acceptable. For engines 5 hp and up, an optional flushing attachment Honda part ZV is available that allows flushing the engine through a port on the side of the gear case.

The prop must be removed and the engine run for about five minutes with either procedure. Either method is acceptable. Midsize engines 25 to 50 hp: Again, the engine must run, with prop removed, for about five minutes. Honda warns that if water pressure is low, tape should be used to close off the engine's water intakes on each side of the gear case. Larger engines 60 to hp: Honda's only recommended flushing procedure is to use the factory flushing port connected to a garden hose with the engine not running.

Outboard Flushing, The Right Way

Mercury's procedure varies by engine size and series. Smaller and midsize four-stroke outboards use the flush port at the rear of the engine. The engine must be warmed up to open the thermostat and circulate water throughout the engine's cooling passages completely. The engine can be vertical or tilted. Remove the prop, and run in neutral at no more than an idle speed for at least five minutes. The water supply should not be opened more than halfway to regulate water pressure. Remove the prop, attach flush muffs so that the rubber cups fit tightly over the water intakes, then adjust water flow so that some water leaks out around the cups.

Start the engine and run at idle speed in neutral for three to five minutes. For flushing without muffs, Mercury offers a garden-hose adapter that connects to a port in the lower engine cowl; this port is accessed by removing a dust cover. Mercury makes special note of using this adapter to drain the cooling water from the engine by disconnecting it from the water-supply hose, then tilting the engine to allow all the water to drain out.

This is especially important in freezing climates.

The Old-School Way

Water pressure no higher than 45 psi should be used. The engine can be running or not when flushing, and flushing should be for at least three minutes. Mercury notes that this procedure should be used when flushing the engine after use in salty or dirty water, and also as a part of preparing the outboard for storage.

No description of using flush muffs is shown in the manual, only the engine's hose-adapter fitting. The description of the procedure is short, noting only that the engine should be off and can be either tilted or vertical. The preferred method is to flush with a flush-muff attachment or built-in port.

With flush muffs, run the engine only at idle speed in neutral for a few minutes while monitoring it at all times for proper water flow out of the tell-tale outlet. There are two possible flushing ports — one on the port side of the engine midsection, the other on the front side of the lower cowl.