1992 40hp Merc Oil Injection Question

I have a 92 40 merc 4cyl that I've owned since it was new but it has done a lot of sitting. I'm planning on doing a tune up on the motor so I can use the boat for shallow water / giging this year.

My question is should I keep it oil injected or convert to pre mix? Are these systems pretty bullet proof on the mercs? I have not had a problem with it yet but I've also never done any maintenance to the oil injection system.

Re: 1992 40hp Merc Oil Injection Question

Man this is like a Ford/Chevy question. I personally like the system. It is nice not having to premix the gas, and the injected mix is a more precise mixture (you dont have to shake the gas tank every time you go out.) But pre-mixing does prevent catastrophe.... Its a tough call, although I'd have a hard time yanking that setup off. All of the older motors I have bought have had them taken off. Does it have an oil alarm?

Re: 1992 40hp Merc Oil Injection Question

Yes it has an oil alarm but I have checked to make sure it still works in a while. But the key does beep when you turn it to "on" like it should.
I just went through the process of disconnecting the VRO oil injection on my 225 Johnson and I'm glad I did I feel a lot better now running it not having to worry about the oil injection crapping out in the middle of the bay.

But I wasent sure if the merc oil injection had a better reputation the the VRO systems.

Re: 1992 40hp Merc Oil Injection Question

The Merc manual for your motor should have the testing of the oil pump supply to the motor in it. Not very hard to test to be sure that it is still working as it should, if you do not want to premix the fuel. If premix is wanted, the easiest way is to cut the hose from the tank to the pump, place a barbed T in it, then run the hose going to the fuelpump to that T. This way the oil in the tank will just recurlate, and it can be hooked back up with just a couple of new hoses later if wanted. You will need to put a small pice of hose on the fuel pump where the oil hose was and seal it off to finish the job. The4 call to keep or premix is up to you. If the spark plugs want to foul from idleing for long perides , you might have to change the plugs to ones reccomeded for a older premix motor. JMO
Oldman570

Re: 1992 40hp Merc Oil Injection Question

Thanks for the replies. I'll check the oil alarm and go from there.

Is there any wires I'll need to unplug so the no oil alarm won't sound off if I go to pre mix?

Re: 1992 40hp Merc Oil Injection Question

When doing the disconnect with a T as I discribe you will need to leave oil in the tank and you will not have to change any wireing. The alarm system will still work as it should, and should not sound as long as the oil leval is enought to keep from setting it off. This way you still have oil to the pump and not be running it in a dry state thus keeping it lubed.It is best to cut the hose from the oil pump to the fuel pump as it should have a check valve in the system . Then all you need to do is plug tat hose.JMO
Oldman570

Re: 1992 40hp Merc Oil Injection Question

If it's working and you're happy with it, why change from injection to premix. Premix can be a pain and you've got convenience now. And your alarms seem to be working. Never hurts to carry a quart or two tucked away in the boat if you forget to top up the reservoir.

Re: 1992 40hp Merc Oil Injection Question

I always run premix my system is completely removed. I never have to worry about my system not oiling my motor. Peace of mind for and old man.

Re: 1992 40hp Merc Oil Injection Question

I don't mind pre mixing it's a 12gal tank , I pre mix with my 225 and a 80 gal tank. I was just thinking that since I've had the motor sitting up for a while and have never done any maintenance to the oil injection I may be able to avoid a engine failure. But it seems like the merc oil injection is more reliable than the VRO system I'll think about it over the weekend while I'm doing some other work to it.