Oil injection?

[CWCW]

In a DFI engine how is the oil injected into the combustion chamber? Is the oil mixed with gas before it is injected into the cylinder? Is this a mechanical injection or an electronic injection?

 

[JB]

Re: Oil injection?

Howdy, CWCW.

In DFI 2 strokes oil is sent to the crankcase, not the cylinder. The gas is injected, electronically, into the cylinder.

Oil is introduced to the crankcase in different ways by different manufacturers. Small amounts of the oil are carried to the cylinder by the airflow through the crankcase.

 

[seahorse5]

Re: Oil injection?

DFI engines use some type of a pressure pump to deliver oil to the crankcase. Yamaha HPDI uses a mechanical pump that only varies with rpm and throttle opening, just like their regular engines.

Evinrude FICHT and E-TEC along with OptiMax use an electric plunger pump that is computer activated to deliver oil to various parts of the motor. The ECU on the motor determines when and how much oil to pump depending on engine load, temp, acceleration, etc.

 

[CWCW]

Re: Oil injection?

I hear and see threads of people talking about the DFI engines blowing up in some past models, is this "blowing up" caused by the engines components that supply the oil into the cylinder failing and the engine ends up seizing because of too little or no oil to lube the engine?

 

[Chris1956]

Re: Oil injection?

CWCW, engines (2 and 4 cycle) do not need to burn oil, in order to be lubricated properly. Therefore DFI motors only inject gasoline into the combustion chamber. Oil comes thru the crankcase with the airflow. All you really need to do is pump the oil into the air stream at the throttle bodies or intake manifold, and it will be circulated.


BTW - OMC uses a high pressure fuel pump to inject the gasoline into the combustion chamber. The Optimax uses a low pressure fuel pump to put gasoline into a chamber next to the combustion chamber and a blast of high pressure air forces the gas into the cylinder.

 

[CWCW]

Re: Oil injection?

I understand how the old 2 stroke carb motors work (mixing oil and gas and then the mixture entering the combustion chamber together and getting burned together, hinse the blue smoke) and i understand how a 4 stroke motors oil never enters the combustion chamber cause it is below the piston down in the crank case. But i must not be understanding how the a DFI doesnt burn oil. So your saying the oil is not burned at all in a DFI 2 stroke motor like a Optimax? I thought the oil was still burned, you just didnt have to pre-mix it with gas and that the rate of oil burned was just more slim than the traditional 2 stroke carb outboards. If a DFI 2 stroke didnt burn a little oil, then why would you ever have to top off the oil reservoil, where else would it go?

 

[seahorse5]

Re: Oil injection?

If a DFI 2 stroke didnt burn a little oil, then why would you ever have to top off the oil reservoil, where else would it go?

A DFI does burn oil, but not as much as a traditional 2-stroke motor. The oil is injected into the crankcase where it recirculates and lubes various parts of the motor. At the same time air is going through the crankcase, as with all 2-stroke motors, and the air picks up oil vapors which are hanging around and all goes into the combustion chamber to be ignited.

 

[Chris1956]

Re: Oil injection?

Seahorse and others, I spoke to a Merc Mechanic/shop owner on this very subject. He has been working on Mercs for a while, and told me that the DFI motor burn the same amount of oil as traditional carb motors, but burn much less gas. At first this would seem to mean that a DFI will operate on a micher richer mix of gas/oil(25::1??), however, I think he means that the DFI motor still operates on a 50::1 gas/oil ratio, but since the DFI motors burn less gas, they also burn less oil, thus maintaining the 50::1 ratio.

 

[TOHATSU GURU]

Re: Oil injection?

Not really true. At WOT they tend to use about the same amount of oil or a little less, but at lower RPMs they use a lot less oil than conventional oil injected engines. The dealer probably has WOT in mind when he was talking to you. Also, the Optimax does use more oil than the Evinrude or Tohatsu DFI models.

 

[seahorse5]

Re: Oil injection?

Seahorse and others, I spoke to a Merc Mechanic/shop owner on this very subject. He has been working on Mercs for a while, and told me that the DFI motor burn the same amount of oil as traditional carb motors, but burn much less gas.

That is exactly what Mercury has been telling their dealers to tell their customers since the Optimax may burn a 30:1 oil gas mix.

Their reasoning is that for example a traditional 2 stroke goes out on a 100 mile off shore fishing trip-50 miles out and 50 miles back- and burns 100 gallons of gas and 2 gallons of oil (50:1).

Then the owner puts on an Optimax that burns 30% less gas per hour but still uses 2 gallons of oil per trip. That math works out to 70 gallons of gas (30% savings over 100 gal. per trip) and the 2 gallons of oil are still needed to protect the motor for 100 miles! That equates to 35:1 gas to oil mix for the Optimax, and sounds worse than the old motor's 50:1 ratio. That is Merc's explanation.

Now Yamaha HPDI and Evinrude E-TEC engines burn less fuel than tradtional motors and less oil also. Most E-TEC owners report about 70-80:1 ratios, depending on how hard the motor is run and how much trolling. That show that the other DFI motors burn less gas and much less oil. For example, the same 100 mile trip an E-TEC should burn about the same 70 gallons as the Merc, but will only use about 1 gallon of oil, compared to Merc's 2 gallon.

Yamaha HPDI is similar, but the 3.1L blocks normally burn around a 40:1 ratio while the smaller blocks are closer to 50-60:1.

 

[CWCW]

Re: Oil injection?

What is about the average cost of a gallon of DFI oil?

 

[TOHATSU GURU]

Re: Oil injection?

Anywhere from $16.00 to $30.00 a gallon depending on the brand, competition and the way in which you buy it. Huge difference between buying a gallon and buying a 55 gallon drum.

 

[CWCW]

Re: Oil injection?

Is there any way to determine how many gallons of gas will be used per gallon of oil? Im looking at a motor in the 90 or 115hp class (DFI motor) and i was wondering how much my spending on oil would be just on fishing local lakes. When looking at 4 stroke vs. DFI 2 stroke (Optimax) i want to determine fuel cost with price of oil on the DFI motor to see how much the extra money for a 4 stroke is worth when compared to oil cost of the DFI motor. I realize this may be a hard question to answer.

 

[TOHATSU GURU]

Re: Oil injection?

Your over thinking this and have some misconceptions. DFI outboards cost more, not less than four-strokes. The operational cost of 2-stroke DFI engine versus 4-stroke is virtually the same. One is not clearly better than another except in terms of an individuals personal boating habit. IE Running at an idle all day with a 4-stroke is probably more efficient than running all day at an idle with a DFI. Pulling a skier up out of the water is easier with a DFI than with a 4-stroke. But, do yourself a favor by not trying to compute theoretical oil usage.

 

[DJ]

Re: Oil injection?

No winner will ever be declared in this conversation.

 

[CWCW]

Re: Oil injection?

Tohatsu Guru,
Actually every dealer i have talked to thats sells Mercury has told me that the 4 stroke equivilant in a certain hp will be around $1000 more than the equivilant DFI motor. Even on Tracker's website the 115 4strokes are at least $1000 more than the Optimax 115 on the same boat. But if the difference is insignificant between the two in fuel cost then you have answered my question.
thanks everyone