# should i trust oil injection?



## littlechub (Aug 1, 2012)

i recently purchased a new to me 2002 basstracker 175 with a 40 hp mercury two stroke. it is oil injected and is the first oil injected outboard ive owned and i am concerned with how trustworthy is the oil injection system? the last thing i want to do is seize a motor as it would be extremely hard to afford a rebuild or replacement anytime soon. thanks


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## crazymanme2 (Aug 1, 2012)

My only comment is, mixing is a for sure thing,oil injection is just a matter of time before it doesn't work. [-o<


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## DaveInGA (Aug 2, 2012)

This sums it up: Not if you want to be sure your motor will not fail from lack of lubricant.


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## Buddychrist (Aug 2, 2012)

Don't trust it at all.

Be safe and Premix all your fuel and use non ethanol gas, your motor will last longer and there will be no worries about correct fuel oil mix

If the oil pump fails and you dry run the engine... Better start looking for a new power head.... Just take it off man


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## Charger25 (Aug 2, 2012)

Well, all I can say is what happened to me. Awhile back I had a 20 ft Cajun bass boat w/ a 200 hp merc. The oil pump ran off a nylon gear at the crank shaft , apparently the gear stripped a tooth . It was still pumping enough oil that the alarm didn't go off but not enough to lube the engine. It seized at 6200 rpm while running 72 mph. It made the most gawd awful screeching and then rattling noise you ever heard, :shock: :shock: That's a sound I never want to hear again. Since then I've always mixed the fuel myself.


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## donmac (Aug 2, 2012)

It would reduce risk, but I haven't heard of too many 2000's and beyond having problems with oil injection.

I had a `99 Mercury EFI 200hp that I bought new and I ran for 10 years with oil injection intact without trouble. That motor ran like a clock and I never even considered removing the OI.

If it were a pre-2000's motor I guess I'd consider removing it. The `94 70hp Evinrude that I'm running on my jet was rebuilt in 2004 and, like most rebuilds, they removed the oil injection as standard procedure. Given the amount that I use it is not that much of a pain. 

There's no way I'd run a big bore motor tournament fishing, without OI - that would be too much of a pain for me personally. But on smaller motors or less frequent usage, where you are not using a lot of oil, those plastic jars with the pre-measured markings work great.


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## lovedr79 (Aug 2, 2012)

another vote for NO! do not trust it.


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## Butthead (Aug 2, 2012)

I had OI on my '87 Merc Black Max 150 and that was awful. The thing always ran oil rich at low RPMs which made it a pain to start just about every time. And when it did start, boy was it a death cloud of smoke that enveloped the boat. Fun times. :LOL2: 

Does your motor have an alarm to tell you if you're low on oil or pressure or anything? If not, then I would ditch it.


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## fender66 (Aug 2, 2012)

I blew up two motors last year that had OI. Neither were my fault. Both were OI fault. No more for me.

Just sayin'.


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## littlechub (Aug 2, 2012)

thanks for the replys fellas, it is a 2002 model motor. it does have the alarms on it but i think when i get this tank of fuel burnt up i will be disabling the oil injection.


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## JRyno10 (Aug 3, 2012)

I would disable/do away with it as well. I have a '95 Evinrude on my 15ft Key West and it blew due to OI failure. We now have done away with it and mix our fuel which I highly recommend.


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## Buddychrist (Aug 3, 2012)

You know someone should invent a gas tank tumbler so that you can just spin a knob and it mixes you fuel without doing the old gas can shaking


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## sixgun86 (Aug 3, 2012)

Everyone I know has disabled or removed their oil injection and premix their gas.


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## turbotodd (Aug 3, 2012)

Where does the Merc 40 inject the oil? Into the bowl or behind the carb throat?

Reason I ask....if it's injected behind the carb throat, you might have to up the main jet size by a little to avoid starving the engine of fuel. Reason being that the jets only flow so much fluid...they're designed to be perfect (or darn close) for gasoline only. Add oil and it displaces a little gas and can run a little leaner. Probably not a big deal on a merc but I have run into it before on a little Yamaha.

I am not familiar with the Mercs but on the Yamahas (the small ones anyway) the oil pump physically cannot fail unless something else causes it to fail. It's a super simple design. Just a gear that runs off the crankshaft more or less. The only "injector failures" I have ever seen were due to air getting into the pump. EIther turning the boat (or watercraft) over/upside down while running or running the tank low and allowing air to get into the line. Once air is in the line, it WILL NOT pump oil, period. It tries to pump air and they don't do a very good job of that. The bigger motors (115+) that I have dealt with, the 2 that were seized were due to a shade-tree mechanic that did not adjust the linkage properly. Too litle oil at WOT. Takes a long time for the damage to be done and the owner (same guy both times) blamed the injection when in fact I found that the link was not reinstalled properly after the carbs were reinstalled. It was buried behind the starter and some wiring so it was hard to get to, but an hour of removal/reinstallation of the starter to gain better access would have saved the owner about $10,000. Same issues when the linkage is removed and then not installed right on some of the 150's that I've seen come from other shops....they'll over-oil at idle and smoke like cheech & chong when started initially. Guy thought it was "normal" but I pointed out what was wrong and he has been a happy boater ever since.

Point being....if you don't know what you're doing with it, dont screw with it.


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## nomowork (Aug 3, 2012)

I had a 40hp two stroke Merc (1996 model) installed on my glass boat recently. It has the oil tank for the gas under the cowling. I asked the shop that installed the motor and controls for me if I would be better off premixing the fuel/oil. The senior and junior shop owners emphatically said DON'T DO IT.

It's been almost a year now and it runs great.


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## TNtroller (Aug 4, 2012)

I would suggest you find out what type of OI your motor has. When OI first came out, it was unreliable, but improvements have been made. When I bought my 04 Tracker new, with a new 04 Merc 60 2s, I asked about the OI alot, and I was told the older/original designs were un-reliable but the newer design (don't know when it came out but my 04 has the new design) is much more reliable. I still use the OI on mine, no issues at all, but I don't dog my 60, I don't think it has ever seen 4500 rpm, 4200 is 26 mph for my rig, which is fast enough for me.


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## fender66 (Aug 4, 2012)

nomowork said:


> I had a 40hp two stroke Merc (1996 model) installed on my glass boat recently. It has the oil tank for the gas under the cowling. I asked the shop that installed the motor and controls for me if I would be better off premixing the fuel/oil. The senior and junior shop owners emphatically said DON'T DO IT.
> 
> It's been almost a year now and it runs great.



I'm interested in their reasoning behind that answer.


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## Rippen Lips (Aug 4, 2012)

fender66 said:


> nomowork said:
> 
> 
> > I had a 40hp two stroke Merc (1996 model) installed on my glass boat recently. It has the oil tank for the gas under the cowling. I asked the shop that installed the motor and controls for me if I would be better off premixing the fuel/oil. The senior and junior shop owners emphatically said DON'T DO IT.
> ...



New motor sales are down ?
but seriously , not meaning to highjack a thread, Ive been debating if i should stop using the OI on my 1991 25hp Suzuki. This motor runs on 100:1 ratio and i have had several people recommend that i should premix my gas at 50:1 and disable the OI. Would it be good for the motor to run it with twice the oil that it is designed to run ?


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## nomowork (Aug 4, 2012)

I can't remember where I read it, but I think the reason they call it a VRO system is that during certain conditions, it changes the oil to gas ratio for some reason.


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## Buddychrist (Aug 5, 2012)

Why would it be 100:1???!!!?!?

That's wayyyyy lean man


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## donmac (Aug 5, 2012)

Buddychrist said:


> Why would it be 100:1???!!!?!?
> 
> That's wayyyyy lean man



OI typically adjusts the ratio based on RPMs. Runs leaner at lower RPMs. While it may be 100:1 at idle it'll likely be much higher at WOT.

Since the early 70's I have had LOTS of motorcycles, snowmobiles, and outboards with OI that have worked flawlessly. If the oil tank ever ran low I made sure to bleed the lines to prevent air gaps. Never had a problem. 

I avoided Optimax when it first came out (99?) due to it blowing up a few heads - but they got that figured out over time. As I mentioned earlier, I'm currently running a 70hp on my jet that had the system removed when it was rebuilt - but overall modern OI systems are pretty darn reliable in my opinion...


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