2001 Merc 135 Optimax Low Oil Sensor

[daktex]

I have read the posts on low oil sensor alarm and just not sure what issue is. motor runs perfect at low or idle speeds but 1 or 2 minutes on plan alarm sounds and engine reduces power to idle speed. It does not die just reduces to idle. I assumed it was a fail safe limp home mode but I read on board motor is not equipped with fail safe low power mode so not sure.

After boat is at idle for 30 seconds or so alarm stops, boat will power back up but again after brief run alarm will sound and again power down to idle speed.

There IS OIL in small reserve and main on board tank!

Unfortunately boat is in Caribbean nearest real dealer 300 miles away and tech that works on it not seems to be stumped. Boat and motor set up in dry storage in states before going down for long time and only has 40 hours on it with no corrosion etc on any leads. I think it is the sensor in tank but the fact that horn does not sound at low speeds makes me think may be different issue like oil pump.

Any help much appreciated.

 

[Texasmark]

Re: 2001 Merc 135 Optimax Low Oil Sensor

Not up on Optimax technology. However, on old designs, like my 2002 90 triple looper, I have a thermostat and a popoff valve. The stat opening temp is 143F and is used below 2500 rpms. Above that speed, the popoff opens allowing a much larger volume of water through the powerhead.

With a 2001 engine, if you haven't changed anything and especially if you run in salt water, and have a similar setup....why not it works, you may have a stuck closed popoff.

SWAG, the computer which the Optimax apparently has, senses the fact that the block temp is overheating when you are operating in the rpm range where the popoff should be open and as a safety measure shuts the engine down to a speed where the tstat can do it's job (apparently it is) and controlling the block temp.

The popoff is pressure controlled. Only way I would know to test it would be to use finger pressure and see if it operates freely. Water pressure is in the order of 10 to 15# so it wouldn't take a lot of finger pressure to move it. If it looks corroded or sticks get a new one along with a new stat as it is probably time to get a new one of those too. iboats sells them.

On the mid range engines both valves are under a shared cover on the top left rear of the block. Just a bulge bolted on. Stat is about the size of a dime and popoff about a nickle or so.

Thinking out loud, Optimax, 135, V engine.....son had a 150 v old design, stat in the top rear of each bank, had pee tube plumbed off stat outlet. Top center of the block, between the Vs was a hose that came off a rt angle hose barb and went down below the powerhead where the popoff valve was located. Yours may be there.

HTH,
Mark

 

[daktex]

Re: 2001 Merc 135 Optimax Low Oil Sensor

Thanks for all the good info. Through reading on this board (very good info) and talking to my mechanic in Dallas have come to your conclusion or mud obstruction in motor. He suggested use laser thermostat to first make sure getting overheat situation if not focus on false sensor is so then change pop off and if that not answer drop lower unit and do some sort of "reverse" heavy flush of motor. Hopefully an avoid later as just serviced lower unit and put new impeller in already.

 

[Texasmark]

Re: 2001 Merc 135 Optimax Low Oil Sensor

Thanks for all the good info. Through reading on this board (very good info) and talking to my mechanic in Dallas have come to your conclusion or mud obstruction in motor. He suggested use laser thermostat to first make sure getting overheat situation if not focus on false sensor is so then change pop off and if that not answer drop lower unit and do some sort of "reverse" heavy flush of motor. Hopefully an avoid later as just serviced lower unit and put new impeller in already.

All the impeller blades intact? No pieces missing?

Mark

 

[redbarnrick]

Re: 2001 Merc 135 Optimax Low Oil Sensor

Do you have the service manual? section C-3 covers the oil injection and has a troubleshooting guide. If you need one send me a PM with an email address I can attach the section C-3, from what I see in trouble shooting if both tanks are full, it says to "Disconnect blue wires going to the low oil float switch int he engine oil reservoir. Check switch for continuity, No Continuity Blue wire is shorted to ground, Continuity, Check continuity with engine running and electrical system under
load. second check, if blue wire had continuity Remove screw and pull out the oil float switch from the tank. Check switch again for continuity, If you have Cont. Oil Float switch is faulty. Replace switch. No cont. on switch, Float in oil tank is faulty. Replace oil tank. hope this helps