If I add 14 gallons of gasoline to our '94 FD and a full 32 oz of TCW3 2-stroke oil, that's a fuel/oil ratio of 56:1, right? (128 x 14)/32 = 56. That seems about right to me, but am I wrong in some way? Also, is it better to pour in the oil first and then add gas for better mixing, or gas first and oil last?

 

Yes, 56:1, and I always do the oil first, so the flow of fuel mixes it.

 

Your math is correct, that's a 56:1 ratio. Seems like a lot of oil though if you're still running the stock OMP too. On the second question, I prefer to add the premix to the tank first, then fill with gas. I have no scientific proof, but it seems intuitive that the act of filling the tank after the oil is added would mix the two liquids up pretty well.

 

You are using an entire 32oz bottle for 14 gallons? Do you still have a functioning OMP? That's over 2.25oz(oil) per gallon of gas. If you have an OMP, I think that is way too much. For my car, with OMP, I am using .5oz of 2-stroke per gallon of gas or for your 14 gallons, I would put in ~7oz of 2 stroke.

Maybe I am doing it wrong, but the only guys I know that run over 2oz per gallon are the ones on Ethanol and have the OMP removed.

I too thrown in the oil before a fill up.

Eric

 

I don’t worry about it, I just fill up and then throw in the premix… but that’s me

Edit…Ethanol here and I run 2oz per gal and sometimes more

Steve

 

Agreed, on both points. The generally accepted ratio is .5 oz. @ gallon with OMP or 1 oz. @ gallon with no OMP. I’m not sure how safe (over) twice that would be over time for a cat , and I would think it would really tend to aggravate carbon deposits and shorten plug life….even with AI. Not to mention emissions in California.
And I too add before fill-up…guesstamating the amount from my fuel gauge on ~16 gallon tank. But thinking about it, it probably would make little difference. The oil is designed to suspend and a couple of turns and the usual road bumps would probably do just as well.

 

That's a 256:1 ratio of gasoline to oil, with OMP functional, yes? I think my relatively new engine has the updated OMP nozzles, which look like seriously less oil flow than the original 1994 types. In the pic below, nozzle diameter looks to have been reduced from 2 mm to 0.8 mm. Is that correct, or am I mis-interpreting the illustration? If so, a "working" system (original oil metering pump plus newer nozzles) would seem to be pushing much less oil than the original.

 

I’m not all that familiar with the later model OMP nozzles but IIRC there was some mention that the dispersion or pattern was improved, but I don’t recall if there was a change in amount delivered. If the former is true, then maybe Mazda felt less would be needed (improved emissions maybe?)
Reguardless, I’ve never seen any other ratios (high ethanol fuel excepted) other than what I mentioned. If you feel the need you could increase it a bit, but not sure about 2 oz. @ gallon WITH the OMP as you initially suggested. That’s quadrupling.

 

I wonder if the theory is to increase the pressure as a result of the smaller.hole? Maybe pushes oil further onto the apex seal and rotor? Pure speculation, but I remember a few threads talking about oil pressure and different jet sizes.

 

I believe this was something of the case IIRC from old research. It didn't necessarily reduce the amount of oil but was supposed to have more of a "spray" affect and less "dropping" of oil for better dispersant properties was the theory. Not sure if it was proven but it makes sense to have oil spread wider rather than dropped mainly in the middle of the rotor if possible.

 

I believe one of the benefits of not shooting oil out a higher pressure was to let the oil wick heat away from the apex seal. As the oil dribbled onto the center of the apex seals, the smearing motion across the face of the housing causes the oil to spread from the center of the apex seal to the outside edges and pulls heat away from the center of the seal with it. There is a paper from Mazda showing their readings and calculations about this. It would seem that keeping the metals cool is also a contributing factor in addition to keeping the seals lubricated in extending seal/housing life.

 

"Apex seal lubrication has become a critical issue. In a race engine, oil supply to the rotor housing by means of injection was precisely monitored and controlled, whereas in the production unit, a larger amount is supplied, just to be on the safe side. Some of the lubricant is fed into the trochoid chamber through a metering nozzle. The previous nozzle's oil passage was 2.0 mm (0.08 in.) in diameter. Negative pressure created in the rotor chamber would cause all the oil within the nozzle to be sucked out. When the engine accelerated rapidly, oil supply could not keep up with the speed. To prevent oil starvation, the previous system supplied a larger amount of oil to be on the safe side. In the new metering nozzle, the passage diameter has been reduced to 0.08 mm (0.003 in.), halving its volume of 0.0005 L (0.03 cu. in.). A new rubber seal is also inserted to fill a gap within the nozzle body where oil used to be sidetracked. Now, there is still some oil left within the nozzle after each suction, so that the lubrication system responds to the apex seal's requirement."

Mazda leaked an SAE paper about the 99 updates, i've seen it a few places.

 

"In the new metering nozzle, the passage diameter has been reduced to 0.08 mm (0.003 in.)"

According to the illustration, the new diameter of the nozzle is 0.8 mm, which is 0.4 of the original (not 0.08 mm).

(If I had to give a name to a 256:1 gasoline-to-oil ratio, I would call it "gasoline.")

 

Well, that IS with an OMP. And I don’t think I went the sarcasm route in my responses, but keep using a quart of oil for less than a full tank of gas…which is about what my 50:1 two-stroke grass trimmer uses, and update this thread in 8 to 10k miles, or the next CA emissions test…whichever comes first.

 

I see your point. Car has just passed its CA emissions with about 16 oz TCW3 per 14 gallons, but have not yet tried 32 oz. Current emissions test results as of 7/19/2024:

Seems okay for 16 oz/14 gals, but you may be right.

 

I'm currently not running an OMP. I run about 9ml / 1L of fuel. I've seen people with an OMP run 3 ml / 1L of fuel