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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11050
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I need advise on the proper way to bleed my oil injection

Customer Question

I need advise on the proper way to bleed my oil injection system on a Mercury 90 ELPTO motor. I am replacing the reservoir tank and float sensor only, and was wondering the level of system bleeding required if only the tank hose is removed?
I have a SELOC manual and the oil bleed procedure has 2 steps, one for the inlet hose/pump bleeding and the other for outlet hose bleeding. The inlet hose is easy enough to bleed using the bleed screw. The outlet is more involved including installing a portable 50:1 premixed gas can. I would need to buy one and not sure where to attach it in the fuel circuit during bleeding of system downstream of the pump.
The manual reads "Any time the oil tank hose is disconnected, the oil injection pump must be purged (bled) of any trapped air..."
If I only disconnect the hose at the tank do I also need to bleed the outlet side of the pump?
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.

Hello. My name is Tan.

Here is the procedure from the Mercury service manual.

I would suggest getting the gas can and mix the fuel oil 50:1 or 2.56 ounces of oil to 1 gallon of gas.

Disconnecting the fuel line does not require purging of the oiling system. The only time you need to bleed the system is when you do oil injection repairs or run out of oil in the tank.

Bleeding Air from Oil Injection Pump
and Oil Injection Outlet Hose
With engine not running, place a shop towel below
the oil injection pump. Loosen bleed screw (a) three
to four turns and allow oil to flow from bleed hole. Retighten
bleed screw. This procedure allows the pump
to fill with oil.
Any air bubbles in outlet hose in most cases will be
purged out of the system during operation of the engine.
NOTE: If air bubbles persist, they can be purged out
of the hose by removing link rod and rotating the
pump arm full clockwise while operating engine at
1000 to 1500 RPM: If necessary, gently pinch the fuel
line between the fuel tank and the fuel pump “Tee” fitting.
This will cause the fuel pump to provide a partial
vacuum which will aid in removal of the air. Reinstall
link rod.

Post back if you have more questions on this procedure.

Customer: replied 1 year ago.
This is what I read in the manual as well, I was looking for an opinion based experience. The procedure has a comment that Any air bubbles in outlet hose in most cases will be
purged out of the system during operation of the engine.
Should outlet side be purged only if air bubbles are an issue?
Expert:  Tan replied 1 year ago.

You will see some air bubbles this is normal. They will purge out. But if you see allot off bubbles purge the line.

Customer: replied 1 year ago.
thanks as an option can I add oil to my main gas tank to assure oil? the only issue is if oil injection working this will result in 2X the oil ratio. will this hurt anything other than maybe fouling plugs? I have a full 40 gallon tank right now so would be a long time on 2X ratio
Expert:  Tan replied 1 year ago.

Yes you can do that it will only foul the plugs. You don't have just a gas can you can use? That is allot of fuel to be running doubled oiling.

Customer: replied 1 year ago.
no don't have portable marine tank just regular gas can which pretty sure wouldn't work
Expert:  Tan replied 1 year ago.

Yes that will work. All you need to do is disconnect the fuel line from the primer bulb tank side get a piece of fuel line connect it to the fuel primer bulb then stick the other end in the gas can. Secure the gas can and run the engine. Once you have seen the air bubbles go away you can go back to the boat tank.