Mercury oil injection system

Robs88

Seaman
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Sep 15, 2008
Messages
51
I just repowered my boat to a 1998 Mercury 115hp, My question is how reliable is the oil injection system on these motors, Or should i eliminate the oil injection and go 50:1 premix?
 

sschefer

Rear Admiral
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Nov 13, 2008
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Re: Mercury oil injection system

I just repowered my boat to a 1998 Mercury 115hp, My question is how reliable is the oil injection system on these motors, Or should i eliminate the oil injection and go 50:1 premix?

I've heard a lot of controversy about your question. I have oil injection and it seems to work fine. All of the newer engines have it also so it doesn't seem to be going away. I've always wondered how you get a perfect 50:1 mix in a large tank. I guess you would need to empty it completely and start from there. After that you'd have to estimate the amount of fuel required and always do the math. I guess you'd need to keep a log or you might end up with too little or too much. A small difference, say 60:1 or 40:1 isn't going to cause any major problems.

If you have questions as to whether your injection system is working there are tests you can do. For the most part, from what I read and my own experience, they seem pretty reliable.
 

Robs88

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Messages
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Re: Mercury oil injection system

Do you know if Mercury kept the same plastic impeller as previous years, or have they upgraded to a aluminum one.
 

sschefer

Rear Admiral
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Nov 13, 2008
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Re: Mercury oil injection system

Do you know if Mercury kept the same plastic impeller as previous years, or have they upgraded to a aluminum one.
Not sure, I've never had my oil pump down that far. Mine tested good at 25ml in 15 min at idle.
 

Sandjob

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Joined
Jul 10, 2009
Messages
56
Re: Mercury oil injection system

premix your fuel. I have blown 2 engines from injection failure. 1 qt of oil every 13 gallons. It takes all the worry and monitoring out. The only exception would be optimax motors. Every mechanic I know suggests it especially when the motor is over 10 years old.
 

j_martin

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Sep 22, 2006
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7,474
Re: Mercury oil injection system

The drive gear on the crankshaft is nylon. They will last forever unless you seriously overheat the engine, or get so much snot in the oil that the pump jams.

The oil injection is quite reliable, but it takes a little bit of operator awareness to keep it reliable.

When you turn on the key, you should get a series of beeps. That's the power on self test for the oil alert module. If you don't hear it, you aren't protected.

If the oil alert does sound the alarm, deal with it. It means trouble, sometimes real trouble, sometimes failed control parts, but it means trouble. You see posts here all the time. "keeps beeping, driving me crazy." :eek: When the engine freezes, it'll be the VRO's fault of course. :D

I beat the snot out of my XR4 all the time, so I run about an ounce of oil per gallon in the fuel tank, plus the oil injection. That gives me about 60:1 at idle, and 40:1 at WOT. It also gives me a few seconds of insurance if the oil pump should fail. One day the oil alert module gave up the ghost about 15 miles out on the Whitefish chain. I dumped the spare quart of oil I had on board into the 22 gallons of fuel I had on board, and kept fishing. I ran back at 1/2 throttle in the end, troubleshot the module, replaced it, topped off the gas tank, and went back to fishing. No harm done except a little smoke.

hope it helps
John
 

Robs88

Seaman
Joined
Sep 15, 2008
Messages
51
Re: Mercury oil injection system

The drive gear on the crankshaft is nylon. They will last forever unless you seriously overheat the engine, or get so much snot in the oil that the pump jams.

The oil injection is quite reliable, but it takes a little bit of operator awareness to keep it reliable.

When you turn on the key, you should get a series of beeps. That's the power on self test for the oil alert module. If you don't hear it, you aren't protected.

If the oil alert does sound the alarm, deal with it. It means trouble, sometimes real trouble, sometimes failed control parts, but it means trouble. You see posts here all the time. "keeps beeping, driving me crazy." :eek: When the engine freezes, it'll be the VRO's fault of course. :D

I beat the snot out of my XR4 all the time, so I run about an ounce of oil per gallon in the fuel tank, plus the oil injection. That gives me about 60:1 at idle, and 40:1 at WOT. It also gives me a few seconds of insurance if the oil pump should fail. One day the oil alert module gave up the ghost about 15 miles out on the Whitefish chain. I dumped the spare quart of oil I had on board into the 22 gallons of fuel I had on board, and kept fishing. I ran back at 1/2 throttle in the end, troubleshot the module, replaced it, topped off the gas tank, and went back to fishing. No harm done except a little smoke.

hope it helps
John


Awesome, As long as its reliable i'll guess ill stick with it. Yes key beeps once from the off to on position.
 

MercGuy

Petty Officer 2nd Class
Joined
Jul 20, 2006
Messages
195
Re: Mercury oil injection system

The drive gear on the crankshaft is nylon. They will last forever unless you seriously overheat the engine, or get so much snot in the oil that the pump jams.

The oil injection is quite reliable, but it takes a little bit of operator awareness to keep it reliable.

When you turn on the key, you should get a series of beeps. That's the power on self test for the oil alert module. If you don't hear it, you aren't protected.

If the oil alert does sound the alarm, deal with it. It means trouble, sometimes real trouble, sometimes failed control parts, but it means trouble. You see posts here all the time. "keeps beeping, driving me crazy." :eek: When the engine freezes, it'll be the VRO's fault of course. :D

I beat the snot out of my XR4 all the time, so I run about an ounce of oil per gallon in the fuel tank, plus the oil injection. That gives me about 60:1 at idle, and 40:1 at WOT. It also gives me a few seconds of insurance if the oil pump should fail. One day the oil alert module gave up the ghost about 15 miles out on the Whitefish chain. I dumped the spare quart of oil I had on board into the 22 gallons of fuel I had on board, and kept fishing. I ran back at 1/2 throttle in the end, troubleshot the module, replaced it, topped off the gas tank, and went back to fishing. No harm done except a little smoke.

hope it helps
John

Just to clarify, the smaller inline 4 115 doesn't have an oil pump rotation sensor (unfortunately). It seems that some of the 1998 115's have a module that sounds a beep when you turn on the key, and some don't (Mine doesn't).

For those that get the beep, it doesn't really tell you anything. The only protection we get on our 115's is low oil level.

I was once told by someone who should know that that 115's used a metal gear to drive the oil pump, but I don't know that for fact.

Mine has over 800 hours and the oil injection is still working fine (keeping fingers crossed) :) :)
 
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