I was having an oil warning alarm last week and the solution was so simple that I'm embarrassed that I didn't see it right away. I had the low oil alarm on my Mercury EFI go off last week (short beeps) but I was in some rough water so I finished the run to the ramp. Put 2 gals of oil in before I went back out a couple of days later and had the alarm go off occasionally in rough water all day but everything seemed fine. Checked the oil tank under the cowling and it was pretty full and was still getting a little white smoke in the exhaust. Got it home and tested the float in the tank under the cowling and it was working so I researched the other possibilities, bad module $200, bad gear in oil pump $1500 but I saw one post that said to make sure the oil tank under the cowling was completely (overflowing) full. Took it out last night fired it up and unscrewed the cap until the tank overflowed. That solved my problem. That float sensor has a pretty short range and with air in the tank it is possible to slosh it around enough to get the alarm. Just wanted to throw this out there as something to look at if you get the oil alarm on the water. But it did make me think and I am now carrying two quarts of oil just in case I ever need to add oil to my gas to make a safe run back to the ramp.

That has happened to most all of the oil blended merc engines. What is happening is that the oil in the large reservior is under pressure (air). The oil will obsorb the air and when the motor sets for a while the air will disappate in form an air pocket inside the small reservior. The small reservior is not under pressure like that of the larger supply reservior... So...over a period of time, you end up with air inside the small tank and like you said, the sensor is very short on range..
That is good news to all Merc owners......

My Evinrude alarm goes off for no apparent reason sometimes. I never let the large oil reservoir get below 1/4 tank but sometimes the "NO OIL" alarm will go off. Sometimes just turning the key off and restarting the engine makes it go away. I usually carry an extra glalon of oil and I will pour it in the reservoir which tends to solve the problem. It has never given me the short beeps like it's low though. It will be a constant loud alarm which sounds like overheat but the low oil light on the dash is on. Oddly enough, it's more prone to happening in cold weather vs warm weather, but not sure why. It always has the oil smoke from two-stroke so I know it's getting oil.

That type of tone is likely to be low oil pressure. You need to check the screen in the oil reservior and most likely replace/rebuild the VRO.

Sometimes it will take 4-5 times of bleeding the small tank to get it corrected. Just carry any tools with you for a couple trips and if it happens back it up to the bank remove the cowling and rebleed the tank. Only take a few minutes.

It's only purpose is for convenience and causing grief, LOL LOL, I am convinced, LOL LOL. I disconnect and add oil to my gas just like I grew up doing. No inconvenience for me. I sleep well and don't have to ever worry about that alarm going off when i have my hands full trying to get thru a storm and back to the ramp safe. Think about it. It happens. Water so rough, you sure as heck don't want to stop, wind howlin, alarm goin off but it aint loud enough to overcome the noise of motor running and wind a howling and then ya stop deader than a flitter. OOPS! Just something to think about. Of course if it's still under warranty, ya caint disconnect or it's voided.

Same thing happened to me. I was told that when your main tank gets low it pulls oil from the reserve and sounds the horn. It will shut the motor down in stages first 3500rpm then 1500rpm till it shuts off. You can still go a good ways on the reserve before it shuts off. (merc. 225 efi)