Pre-mix in the RX-8 may not be a good idea
 

I was just thinking about the benefits of premixing oil the other day when this hit me. The Rx-8 saddle tank might only allow the the premix oil to mix with half the gas. The end result would be running half a tank with no or to little oil.

I took a quick look at the fuel tank diagram and it show the fuel filler line going into the drivers side of the fuel tank. That means that the only chance the oil has to mix with the fuel that eventually spills over and fills the passenger side is as the tank is being filled. In a regular gas tank the oil will mix as the car is driven and the gas splashes around, This can not happen with the saddle tank.

That is correct. I add premix when I fill-up.

Should be (pre!)mixed nicely.

just dump it in before filling up.

meh premix. I just put gas in mine and it runs damn fine, like 99% of the other rx-8 owners.

Were are using so little oil, I dont think this is an issue. Not like a dirt-bike that runs 34-1 which would require mixing in a seperate container before dumping into the tank.

Thats why u dump the premix in before fill up ?

Thanks for the input.....
 

So, you shouldn't pre-mix because half the tank might not get any oil :boring: ?

Ergo you should modify your pre-mixing method, right?

A little knowledge is a dangerous thing.

S

I haven't heard much to alter my initial thought. Even if you dump the oil in before filling you are in all probability going to get a different mix ratio in each side of the saddle tank. Weather that mixture in one side is too diluted to properly protect the engine is the question. I do feel it is enough of a concern to negate the advantages of using a premix.

if you don't want to, don't do it. Most of us still have the OEM MOP installed and active, so this is just added protection should Mazda suddenly find that issues remain with seals and oil delivery inconsistant.

4oz is such a tiny amount in 15 gallon fillups that it could not cause damage even if you had all your oil going into one side of the tank - ignoring the fact that we would not be filling up from an empty car, but one that stil has 1-2 gallons in the bottom.

There is an active transfer from one side of the tank to the other that will mix the fuel.......this is not a problem that will be borne out in reality.....as long as you add the oil before the gas when you fill up

Two questions.

Has there been any considerable evidence that premixing will keep the exhaust tips clean? (this came up in another thread)

Also, anyone do this in New Jersey, where attendants are legally required to pump the gas for you?

Logic....
 

Rudimentary logic would dictate that adding more oil to an oil burning system should not give LESS soot at the tips.

Empirical evidence would indicate that the only verifiable result of pre-mixing is a subtle warm and fuzzy feeling produced in the owner.

S :)

Before premixing, my exhaust tips would be covered in a black thick film between weekly washes.

After premixing, the tips still get dirty, but the film is much lighter in color and thickness. It is quite mild and not at all black like it used to be. It's a very light tan color, and you can see through it - so it still shines.

So to answer your question: Yes, premixing for me has removed dirty exhaust tips.

I was under the assumption that the MOP would be disabled when using premix. If you don't disable the MOP what's the point?

It is my understanding that the transfer only happens once one side is empty, then the other side is pumped into it. If this is correct then you could still have a problem.

It's insurance. Your car will still get oil even if your MOP fails, or if the required amount of oil being metered is incorrect.

It would likely be even better to get rid of the MOP completely since 2 stroke oil is nicer than the used engine oil, but this is a simple thing to do and the engine does seem to function better.

Scenario.....
 

It is my understanding that the transfer only happens once one side is empty, then the other side is pumped into it.

Another interesting theory, mugged by a vicious gang of facts!

How would the timing of that work?

How would the level sender work?

How would you keep the two "tanks" apart, when there is not even a baffle between them?

Etc..

S

Not sure what you're getting at, Stealth.

If you're saying premix doesn't work, there's a lot of rx-7 guys who'd disagree.

Not me......
 

I never suggested pre-mix wasn't a good idea - used it myself since Day1/Tank1!

Just trying to refute the theory that it won't mix in a saddle shaped tank, it will.

I use 200ml of ISO-GD two-stroke, 200mls of UCL, 100mls of fuel grade IPA, and a lubricity additive. This mix may be overkill...... :wink2: but my housings will be nice and shiny for a LONG time!

I always said the MOP on the RX-8 is cut back too far, to please the "average" owner.

Usually put five gallons in, then add the mix and top off.

S

oh, okay.

I thought when you said this:

You were talking about premixing, and how the oil would be metered into the engine properly.

Isn't 2-stoke oil and UCL essentially the same thing?

Your brew sounds almost exactly like FP60. Wouldnt' it just be easier to run FP60?

I could be wrong. It was relayed to me that once the one saddle tank empties at the half way mark the other side is pumped completely into the now emptied tank. Based on the behavior of the gas gauge this would make some sense and the tank diagrams indicate that it could function in this manor.

Do you know for a fact how the gas tank works?

If you do and I am incorrect I would like to learn how it really dose work. You have provided no fact only technical issues which any competent engineer could easily resolve. If you don't know for a fact how the tank works then there is a very good chance that your safety net has holes.

from the drawings it looks like the fuel pump suction is used to siphon the fuel from the one side to the other

Something strange happens with the fuel tank.
This is from the online service manual:

(quote)
When the fuel gauge indicates 3/4 or more, the fuel level is higher than the installation surface of the fuel pump and the fuel suction pipe bracket. Due to this condition, fuel may spill or leak out when performing this procedure. Before performing this procedure, always drain out fuel so that the fuel tank is half full or less (according to the fuel gauge needle).

(1) Disconnect the quick release connector (engine compartment side). (See QUICK RELEASE CONNECTOR REMOVAL/INSTALLATION.)

(2) Attach a long hose to the disconnected fuel pipe and drain the fuel into a proper receptacle.
(3) Ground check connector terminal F/P to the body using a jumper wire.

Caution

• Shorting the wrong terminal of the check connector may cause malfunctions. Make sure to short only the specified terminal.

(4) Turn the ignition switch to the ON position and operate the fuel pump for approx. 20 min.

Caution

• The fuel pump may malfunction if it is operated without any fuel in the fuel tank (fuel pump idling). Constantly monitor the amount of fuel being discharged and immediately stop operation of the pump when essentially no fuel is being discharged.

(5) When essentially no fuel is being discharged from the hose, turn the ignition switch to the LOCK position.

Note

• When operating the fuel pump with a full fuel tank, fuel discharge will become erratic after approx. 10 min but will continue for approx. 10 min more and then essentially no fuel will be discharged. At this time the fuel gauge needle will be at the halfway position.
(/quote)

That would indicate to me that the fuel tank either relies on sloshing to distribute fuel (my motorcycle does this), or there is some sort of special pickup or hose that distributes the fuel. This would also explain why the fuel gauge tends to be a bit imprecise.

the service manual shows a tube in the one diagram (but the picture seems to be a bit wacky as the tube is shown going through the fuel pump but the fuel pump only has 1 fitting)... hence i'm guessing the tube goes near the fuel pump suction line and siphons the other side of the tank

Oil in the tank
 

These "theories" of how the tank works are crazy. The fuel can get everywhere in the tank without isolation, thats for sure. I don't believe this pumpiing stuff at all. As for mixing before or after you fill, this is basic CHEM 101 stuff. The 2-cycle oil and gas are both Hydro carbons and 100% compatible. Surely they mix together all on there own at 250:1 ratio or leaner. There can be no "hot spots" of concentrated oil/gas except for the first moments when they meet.

Who thinks otherwise, I mean Come-on fella's. Drive it and that's what works!
Jeff B.

Isn't there is a jet pump in the tank or whatever they called it. Even with the lack of return line, the excess fuel from the pump will have to go somewhere creating its own fuel mixing mechanism in the tank all the time. I often put in the 2cycle oil after a full tank filled up when my bottle is empty at the gas station. I woudn't be worry about it; those oil mixed with the fuel pretty well in those low ratio.

The fuel is siphoned from the passenger side using the discharge of the fuel pressure regulator on the pump (in the drivers side tank) I know that..I have modified my fuel system...and left the siphon intact so that it will work normally. The passenger side of the fuel tank is empty at about 1/3 tank without any transfer from G loading in corners.....

Sorry for reviving this thread, it's been going on in my mind.
1. I premix every 4ml for 1liter of gas (as suggested), but i dont daily drive the 8, maybe once or twice per month, i pour the idemitsu premix first before filling up. my concerns are, if the car sleeps for a month, will the 2 stroke oil separate itself from the gas in the tank ? if yes, will it be dangerous/bad?

The premix available in my country :
Idemitsu 2T FC SS - Idemitsu

I doubt it will separate or stratify but, even if it does, it should mix pretty quickly at idle.

A healthy fuel pump pushes more fuel than the engine needs. The pressure regulator routes the excess fuel back into the tank. In the process, the fuel passes by a venturi system that draws fuel in from the passenger side of the tank. Mixing is a byproduct of this design.

If you're extra concerned, turn the key to "Run" but don't start. This turns the fuel pump on to prime the fuel system. Since the engine is literally using zero fuel, it will start mixing. I don't know how long the pump runs during priming but you can turn the key on and off a few times to make sure.

Nothing to worry about. The salt will separate in the ocean before premix does in the fuel tank.

Thanks for answering!

lmao

thanks for that gem.

beers :beer:

The solubility of one petroleum solvent in another petroleum solvent probably doesn't change very much as a result of the base stock.

Maybe if there were a difference in hydrogen saturation but the refining process usually takes care of that pretty well (minimizing aromatic content is usually a design intent with petroleum refining catalysts).

To extend Loki's analogy, the difference in solubility between synthetic and natural salt in the ocean would be greater than the difference between synthetic and dino 2-stroke in gasoline.

Your comment about synthetic 2-stroke oil not mixing with diesel got me searching. I can't find any actual evidence that this is true. I'll have to try this at work. I have some Lucas synthetic 2-stroke and I work with petrochemicals in the diesel range every day.

Yeah i remember seeing the diesel results and synthetic 2 stroke didn't mix well at all but mineral mixed well. Would be good to see a petrol test

Best way for you to see that test would be to put some gasoline into a clear container and add an appropriate amount of 2-stroke. Mix thoroughly and wait for it to separate or stratify.

Don't forget that these kinds of tests are easy to accomplish and you don't need special equipment, training, or facilities.

Just do it in a well-ventilated area and pay very close attention to all potential ignition sources.

What do you think happens when you drive around.... and when you add the gas to the tank in the first place...

This is such a hypothetical problem. The bypass of the fuel pump will mix it up as well...

I know some premix doesn't work well with ethanol fuel, so could be the same problem here.

Again, where are the data to back that up?

TBH I am just as curious as you are. Not that I use ehthanol fuel.

Yes... it's not an issue.

As for the different premixed for Alchohol fuels.... that is true... but it isn't because it doesnt stay mixed... it's mainly because the alcohol requires different lubricants to do its job properly