Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

[ortho85]

Was about 20 mins out on the river when the engine alarm started a continuous tone - no bipping, just straight to full scream.

This Forum and others say it's a faulty sensor (see below), and my question is can I just leave it disconnected until it's next service, which is 9 months away?

Why I say it's the sensor -

• water flowing normally as coolant
• no signs of the "Engine Guardian System" affecting speed - had to get back to dock, and it ran at 4000 revs normally (but screaming!)
• oil level OK
• waited 2 hours to be sure engine cooled, but still alarm sounding
• disconnected the lead with the tan stripe from the bottom of the oil tank, and the alarm stops.

Secondary question - how easy is it (for an amateur) to replace the oil tank - which Dr Google says is how you replace the oil sensor?

Thanks,

BK

 

[wired247]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

Sounds like a good time to pull that junk and run premix.

 

[Iceman66]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

Here are some words about removing the oil injenction system.http://forums.iboats.com/mercury-mariner-outboards/eliminating-oil-injection-system-613987.html

To wired247: Changed your opinion?

 

[Silvertip]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

There is no reason to remove or disable the oil injection system. Fix the alarm. If you know which end of a screwdriver to hold you should be able to remove and replace the tank.

 

[wired247]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

Here are some words about removing the oil injenction system.http://forums.iboats.com/mercury-mariner-outboards/eliminating-oil-injection-system-613987.html

To wired247: Changed your opinion?

Yes actually. I used to really like them. Now I think that for a GP motor if the injection starts to go bad, let it go. Ive just torn into too many in the last year to see what light oiling at idle and transition to full will do. Now I overoil the bejesus out of everything and I sleep better.

 

[joed]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

The oil tank fault is normally not a continuous beep. Continuous beep is often the oil/overheat module that combines the two sensors into one wire. Oil tank fault(blue wires) is a beep beep beep...
Serial, year and model number will get the proper drawing and confirm this.

 

[Texasmark]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

Depends on engine electrical system. Some have an alarm module others no module. With no module there is nothing to modulate the alarm. When a fault occurs, the engine provides a ground to the horn and it sounds a monotone regardless of the source of the ground. If you have a module, the oil fault is fed into the module where it is chopped to provide an intermittent beep beep and then out on the same wire as the OT alarm to the horn. The reason is identification of the fault. My service manual has numerous wiring diagrams for the same year model/hp engines and it just depends.

I disconnected the drive gear on my '02 90 triple a couple of years ago. Figured the engine was old enough and I just didn't want to be concerned about it. Had no problems with it at the time. All I did was to pull the pump, remove the drive gear and replace the pump. Shaft bushing remained tightly in place so I left it. The tank was about half full and I left it that way and put a mark on the tank showing the level when I removed the pump. It's still there. I run Pennzoil premium syn blend oil at 50:1 and can't tell the difference.

"Different Strokes for Different Folks". aka some TV show with a little guy..."All in the Family" kind of soap.

Oh and I wrote on my boat adjacent to the gas filler neck: 1 pt oil to 6 gal. Been a long time since you had to premix and I didn't want to forget.

Mark

 

[ortho85]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

The oil tank fault is normally not a continuous beep. Continuous beep is often the oil/overheat module that combines the two sensors into one wire. Oil tank fault(blue wires) is a beep beep beep...
Serial, year and model number will get the proper drawing and confirm this.

This one's owner's manual says the continuous beep can be oil failure or overheat - same noise.

It's a 2005 75ELPTO, with serial number 1B286492.

Thanks for all the input. Now to try to find a schematic for the oil tank replacement.

Cheers,

BK

 

[Texasmark]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

This one's owner's manual says the continuous beep can be oil failure or overheat - same noise.

It's a 2005 75ELPTO, with serial number 1B286492.

Thanks for all the input. Now to try to find a schematic for the oil tank replacement.

Cheers,

BK

Don't understand the statement. With no modulator module, the wiring is: Tank has 2 Light Blue wires. One goes to ground...engine block aka battery -. Other wire jumpers within the engine harness to the tan light blue OT alarm wire. If the oil level shorts due to low oil in the tank, or the OT shorts due to an engine block temp above 195F, you have a ground on the low side of the alarm and it will sound a continuous tone as long as the ignition key is not in the OFF position. The short circuit to ground "alarm signal" goes out the tan/lt. blue striped wire via pin 3 of the 8 pin engine wiring harness to the remote wiring harness and on to the low side of the horn. Top side of the horn is tied to a purple wire which is 12v switched on by the ignition switch in any position other than OFF.

What else do yo need to know?

Mark

 

[ortho85]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

Hi Mark,

I meant that it seems I have to replace the entire tank if I want an oil warning system that works. So I'm looking for something to guide me on this.

Or I may just leave the wire disconnected.

However that's not really in my blood!

Cheers,

BK

 

[MikeB0307]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

I hate to say it, but replace the sensor. Think of what it will cost you to rebuild/repair the damage if you forget that its unhooked and run out of oil. (It can happen!)

 

[Texasmark]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

I hate to say it, but replace the sensor. Think of what it will cost you to rebuild/repair the damage if you forget that its unhooked and run out of oil. (It can happen!)

In the old days all you had was premix and it was a no brainer. After being spoiled for a number of years and going back, as I said, I wrote on my boat next to the gas fill to add oil to the gas. Then I didn't have to worry about remembering......but I don't have Altheimers.

Mark

 

[oldman570]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

I have a 1987 70HP that I have run on premix for more than 10 years with no trouble. It is disabled as I stated in http://forums.iboats.com/mercury-mar...em-613987.html. The only other item that I changed is to run NKG BUHW plugs in the motor, and I replace them every year, needed or not, when I service the complete motor. My motor did not have the modual and just has the oil sensor wired straight to the overheat and alarm horn. The oil sensor can be replaced without replacing the oil tank on my motor. JMO
Oldman570

 

[CharlieB]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

Odds are it is NOT the oil tank sensor, rather the adhesive failure, the magnet fell off the oil level float that surrounds the sensor.

I have yet to replace a sensor, but replaced LOTS of tanks.

The test will be to remove the sensor from the tank, reconnect the wires, turn the key on, no sound, replace the tank, which you have to remove in order to pull out the sensor.

 

[James R]

Re: Faulty oil sensor in Mercury 75 two stroke - OK to disconnect?

This tank failure is so common that Mercury should have done something about it. Very rare for the sensor to fail and yes if you need the alarm to work replacing the tank is the only way. I run several boats and different motors and rebuild them. My 60HP Big Foot has a window in the cover so a simple check before you start out should be sufficient. One other thing about these merc oil systems. If you have the short oil feed hose to the pump it can and will brittalize and break over time and the oil will not get to the pump. Check this periodically. If you need to replace it use the merc product. It is at least somewhat predictable.
If you determine that you want to run 50:1 without the merc oiling system be sure to remove the drive shaft from the pump. If you dont the pump running dry will seize and the shaft will rip up the drive gear on the crankshaft. Bits and the bolt into the cylinders.

 

[woodyct]

Having the same issue on a 2000 Merc 90 Hp. Plan on replacing the tank and sensor this weekend, but had a question about bleeding the oil system. I have a SELOC service manual that mentions oil system bleeding if hoses removed which includes the pump inlet hose, pump and outlet hose, but I assume the outlet side is only if you remove the pump or hoses downstream of the pump????

Under the section in the SELOC manual for replacing the oil tank they have a warning note that reads "Any time the oil tank hose is disconnected, the oil injection pump must be purged (bled) of any trapped air...." This leads me to believe that the downstream or outlet hose side of pump does not need to be bled?????

The outlet side of the pump bleeding process seems a little more involved than the bleeding of the pump and inlet side which is just opening the bleed screw and allow a continuous flow of oil.

Can anyone advise if my assumptions are right??? If not what is the process for running off a pre-mixed tank when the motor is normally running off an in hull fuel tank and not an external portable tank... disconnecting the onboard tank and connecting and running off the external fuel tank while still allowing the oil injection pump to operate and purge air out of the outlet hose????

Thanks