Question about Oil Injection Problems on outboard

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I have a Mercury 75hp outboard, about 20 years old. Yesterday the low oil indicator went off while trolling. It was not low on oil but I added some anyway. That did not help. While trolling the motor would at times run very rough and actually sounded like it had no oil mixed. Decided to head to boat ramp and when I increased the rpm's the motor ran smoothly as normal and buzzer quit. Decided to stop and fish a little more and same issue. Ran rough and buzzer went off. Increase rpm's and runs smooth and quiet.

Any suggestions as to a possible problem. How does the injection system work? Is it possible that a pump or something is bad and produces enough oil at higher rpm's or a screen or filter that is partly blocked. Looking for any suggestions.

Thanks
 


nytebyte

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Might have been running a little hot? Water have a good stream out of the indicator? That oil injection systym is normally problem free. Just guessing here.
 

AaronJ

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Sounds like a weak oil injection pump. Some guys just mix if the pump fails and don't want to spend the $$ to repair.
 

REY_off

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Are you sure it was the low oil alarm and not a high temp alarm?

The symptoms you describe sound like a high temp alarm from a worn out water pump impeller. The increase in RPMs increases the flow through the motor cooling it back down, and then when you slow down to troll the worn out impeller doesnt provide enough flow to cool the engine.
 

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Are you sure it was the low oil alarm and not a high temp alarm?

The symptoms you describe sound like a high temp alarm from a worn out water pump impeller. The increase in RPMs increases the flow through the motor cooling it back down, and then when you slow down to troll the worn out impeller doesnt provide enough flow to cool the engine.

It's certainly worth another look but pretty sure there was a good stream. Thanks. I admit that sometimes my memory isn't what it used to be but I think I remember checking that when I started the motor.
 


WormWiggler

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If I am recalling correctly, my low oil alarm went haywire and the shop said the float loses it's bouyancy or some such shit. I disabled it and went on with my life. I checked and topped off the oil every trip.
 

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If I am recalling correctly, my low oil alarm went haywire and the shop said the float loses it's bouyancy or some such shit. I disabled it and went on with my life. I checked and topped off the oil every trip.

I could live with that except there is a big difference between how the motor runs at low rpm vs higher rpm. Either too hot at low rpm or not enough oil at low rpm i'm thinking.
 

REY_off

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It's certainly worth another look but pretty sure there was a good stream. Thanks. I admit that sometimes my memory isn't what it used to be but I think I remember checking that when I started the motor.

I've seen boats with good streams that still overheat from a worn out impeller. On a lot of motors, the tell tale is not a great indicator of proper flow because of where the tell tale connection is located on the block/motor. The tell tale is more of a flow/no flow quick reference, but not of proper flow amount. If that makes sense....

River sand is hard on those little rubber impellers. Most good mechanics will tell you to replace them every other year just to save a headache at the worst possible time of the year, like right now when all the shops are backed up 1-2 months.
 

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Thank you for the suggestions, especially those of you who thought of a water pump issue. After some of you suggested a possible water issue, I did remember kicking up quite a bit of mud after unloading. You were correct, the issue was water pressure, not oil which is most likely much easier to fix. Will be back running shortly.
 

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