203 Mercury 125 Saltvwater-oil in carbs and fuel line

Twice recently I've found oil in the fuel line for my 2003 Merc 125. This seems to occur after the engine hasn't run for 48 hours or longer. As near as I can tell it's flowing through one or more of the carbs. I suspect that the check valve in the top of the oil reservoir has failed and that as fuel drains back into the tank over time it is siphoning oil back through the system.

Also, to top things off, there is an engine alarm going off. There is oil in the reservoir, the water pump is working well, and the engine block is not hot to the touch. I strongly suspect the oil level sensor failed. It's done this once before.

Two questions:

Any other ideas about oil in the fuel line?

Can the oil level sensor and check valve be replaced on the reservoir or does the entire reservoir assembly need to be replaced?

Thanks folks.

Where in the fuel line is the oil? That motor puts oil into the fuel line before the fuel pump. There is a check valve that should stop that from getting back to the tank.

It's between the engine and the priming bulb.

I found the check valve downstream of the oil pump and upstream of the carbs. I guess it's better to be stuck open than closed. I have a new question. Is the alarm re: 2 cycle oil only related to oil level in the reservoir, or could it relate to lack of flow thru the oil pump or some other part of that system?

No That is a really good system so the only alarm is oil level. Those sensors do go bad.

Today I replaced the 2 check valves (oil to fuel line, and oil tank vent) we will see.

I also replaced the oil level sensor. I'm still getting a constant alarm with the key switch on. The sensor has two blue wires coming out of it. But those connect to a black wire and a brown wire. I marked one of the blue wires and tried connecting it both ways. I still get a constant alarm. I refilled the oil reservoir to about 1/4 to ensure that the sensor was fully submerged but I still get a constant alarm. The engine is cold and it's not been over-revved.

Is there a reset for the alarm? Is there a test procedure I can use? I would appreciate any advice. Thanks

Change the pulse check valve on the engine. You cannot clean it, just replace it. This check valve pressurizes the reserve oil tank and lets the pressure out when the engine is shut down. If the tank stays pressurized after shut down it will over oil the carbs while it sits.

flyingscott said:

Where in the fuel line is the oil? That motor puts oil into the fuel line before the fuel pump. There is a check valve that should stop that from getting back to the tank.

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If your motor has a oil reservoir under the cowling and a remote oil tank to fill the reservoir it is under constant pressure even when the motor hasn’t run in days it has been my experience that the oil will force its way in to the carbs and the motor won’t fire until I drained the carbs. So after every use I crack the lid on the remote oil tank to release the pressure and it has stopped the flow of oil in to the carbs.do not try to release the pressure from the reservoir on the motor it will cause a huge mess.

If this is the 4 cylinder 2+2 motor oil is gravity fed not pressurized....

No remote oil tank on that motor only the tank under the hood.

faztbullet said:

If this is the 4 cylinder 2+2 motor oil is gravity fed not pressurized....

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Maybe you can help me. I have a 2001 mercury 150 saltwater edition 2 stroke with a remote oil tank the engine runs great idles good and runs great at top speed. Recently while at trolling speed the motor shuts off with out warning. No sputtering no hesitation. It will fire right back up most of the time but the more often it stalls the harder it becomes to start. When it gets to that point I have to push the button in the middle of the shifter, and throttle if down to start it. Any ideas why it stalls?and what’s needed to cure the problem?

Shaggy6795 said:

Maybe you can help me. I have a 2001 mercury 150 saltwater edition 2 stroke with a remote oil tank the engine runs great idles good and runs great at top speed. Recently while at trolling speed the motor shuts off with out warning. No sputtering no hesitation. It will fire right back up most of the time but the more often it stalls the harder it becomes to start. When it gets to that point I have to push the button in the middle of the shifter, and throttle if down to start it. Any ideas why it stalls?and what’s needed to cure the problem?

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For starters, you can start your own thread and not hijack other peoples.