Premix your 8, get better gas milage [Archive]

fikren

03-06-2008, 04:39 PM

Well I started premixing my 8 and noticed an improvement on gas milage. I am taking my numbers based on the 1/4 tank marks of the fuel level gauge.

Between all the tests I have not changed my driving style, have not been taking different driving routes, and have not experianced any traffic or long time idling periods that would make the numbers change.

Prior to premixing I was seeing on average about 50-53 miles per 1/4 and this was consistant through all the 1/4 tank marks and also mainly based on the 1/4-1/2 tank, 1/2-3/4 tank, and 3/4-full tank. I never ran the car empty enough to justify using the empty-1/4 tank for my numbers.

So essentially at each 1/4 mark I had traveled somewhere between 50-53 miles.

After premixing I am seeing 55-60 miles traveled per 1/4 tank of gas. This is equating to 15-20 more miles per tank of gas while premixing then then when not premixing.

So not only can premixing offer you increased apex seal lubrication but can also help on the gas milage. Others have also said that premixing will make your car idle a little smoother. Since my engine is pretty much new (~1400 miles) I really haven't noticed any difference in the idle.

Just thought I would share.

Jonathan

ScreaminRX8

03-06-2008, 10:04 PM

So what are you using in premix and how much?

With mine I notice I get about the same as you from full to 3/4 but from 3/4 to 1/2 I get about 75 miles. I can't really complain about gas mileage after I have heard some of the mileages people get. I drove to Tampa FL in Jan of 07 and averaged 24 to 25 miles to the gallon at 70 to 75mph average with the exception of the construction zones.

fikren

03-06-2008, 10:23 PM

Premix wise I am using a walmart brand tc-3. Cost wise you can't beat it. I think when I went and picked some up I bought a gallon of it, a 16oz bottle of it (to use as the mesuring device) and a long necked funel and paid ~11 bucks for it all. I actually went with the walmart brand as Kevin made mention of it in another post and with 125K+ miles on his car I think its doing its job.

I mix 8oz per tank of gas.

I am going to run a couple of tanks where I am basing the findings straight off the odometer rather than the fuel gauge both with premixing and without just to verify that there is indeed a gain from premixing. Right now for example I am sitting just barly above a 1/4 tank of gas and the trip meter is reading 176.4 normally without the premixing it would be reading about 145-150 at this point. I don't think the fuel gauge would be reading over 25miles off but I will be doing the straight number calculations starting with my next fill up just to make sure.

ScreaminRX8

03-06-2008, 10:56 PM

Thanks! This is something I am going to look into getting and trying it out and see if I can see a difference! anything to help out on gas mileage! these days that is a must!

fikren

03-06-2008, 11:01 PM

This is something I am going to look into getting and trying it out and see if I can see a difference! anything to help out on gas mileage! these days that is a must!
No kidding and from what I'm hearing its only going to get worse (price wise) over the next few months. :(

Herblenny

03-07-2008, 05:24 AM

I might have to try this... as my MPG have dropped! I was averaging about 18-19 when I first got my 8 and now I'm avg. 15-17MPG. I know I drive fairly hard, but I say not much different than before..

I'm going to pick up a gallon of 2cycle and give it a shot this weekend.

Lets all give this a try and report:) I usually fill up my tank around 1/4 tank (160-190 Mile). Last night it took over 10 gallons fill to the top and I drove 155 miles.

fikren

03-07-2008, 10:47 AM

Well I filled up this morning, it appears that I gained about 25miles/tank since premixing. I am going to keep actual numbers this time as far as odometer reading, gallons of gas bought, etc. I should have a more concrete number after 3-4 fillups and working the numbers out.

Worst case is your not increasing (or just barely) your MPG but the premixing can only help with seal lub so either way I think its a good route to go.

Pink Flea

03-07-2008, 11:13 AM

I have been using the Pettit racing premix for a while. My car feels like it idles smoother but I havent noticed a change in my mileage, but I dont pay attention to it in the first place.

ScreaminRX8

03-07-2008, 10:50 PM

Well I am going to try this and see how it works out!

WE3RX7

03-10-2008, 04:21 PM

fikren

03-10-2008, 05:54 PM

Good news considering I'm starting to premix on my engine now as well.. I'll have to start calculating the difference in MPG too.

I'm curious why premixing gains MPG though... I would assume the PCM would manage most of that, is there something that would detect the additional level of oil in the fuel? What would create this change?

I'm curious myself as to why it might increase MPG. Don't have the answer there, I just know that I have increased my overal milage after premixing and my driving style or conditions have not changed between the non premixed tanks of gas vs the couple of premixed tanks I've run.

It would be interesting to see peoples various results between running it and not running it.

85rx-7gsl-se

03-10-2008, 06:05 PM

Well, my guess would be less

A) Less Friction
B) Better compression means more of the energy created from the combustion process is transferred to the rotation of the rotary rather than slipping past the seal
C) The oil burns more slowly than gas ensuring a longer, cleaner burn

WE3RX7

03-12-2008, 10:07 PM

Just filled my tank back up w/ some 2 stroke - we'll have to see what I get. Last full tank went 280 miles last go (all city, no real highway) so we'll see what we get this time w/ the same kind of driving.

Herblenny

03-12-2008, 10:27 PM

WHAT 280 miles on a tank! Yikes!~! I get under 200 per tank in the city!

I just put 2 stroke and filled it up today.. We'll see what happens..

I8U

03-13-2008, 07:55 PM

I pulled 325 miles out a tank with 6oz of RP TC-3. Granted it was all highway miles, but none the less that is still some great mileage!

WE3RX7

03-14-2008, 10:30 AM

Yea 280 all city. My GF drives the 8 daily an her round trip with work is about 6 miles or less a day. I drove it around town a few times, but never saw any highway on that tank and the light JUST came on at 280 miles before filling it back up..

My GF also barely sees RPM higher than 5k from what I can tell though - I keep telling her to push the car more. Thats why I drive the hell out of it when I get a chance - keeps the carbon off :)

fikren

03-16-2008, 02:34 PM

I'm still seeing about 230-250 miles per tank premixing vs 200-220 not premixing. I will probley never see 280 or better because frankly I drive the hell out of the car. I'm opposite your girl, mine probley never sees below 5k rpm other than taking off in first.

Herblenny

03-16-2008, 05:47 PM

Update... I still have over 1/4 tank left... I'll be filling it up this week (Tuesday). But so far, Looks like Premix is in fact increasing MPG. Normally, I see less than 100 at 1/2 tank mark and I now see over 100 at 1/2 tank mark. I'll post here when I fill up on tuesday.

WE3RX7

03-16-2008, 07:30 PM

Well I had to fill up again after a long road trip w/ me driving - went 240 miles of highway/city mix with ME driving and driving hard! The tank took 14g to fill it back up, so really - to get to empty we could have put at least another 25 miles on it, so saying 265 of me driving vs 280 w/ the GF driving.. .I'd say the premix helped.

This week will be a better test though - I'm shooting for 300 to the tank w/ the GF driving, lol.

Herblenny

03-17-2008, 12:10 PM

I8U

03-17-2008, 08:39 PM

^HAHA! I know why you get shitty gas mileage Phil...it's cuz you have Lightning Yellow! :)

fikren

03-17-2008, 08:44 PM

OK.. I filled up my tank today and here is my result..

10.1 gallons
166 miles.

16.6ish miles per gallon!!!

So, I have to say, didn't do much difference. I put more two cycle and we'll see next time..
Any idea what your fuel filter looks like, tire wear/pressure? What would you call your driving style (average 3-5k rpm, average 5-7k rmp, or average redline). Do you end up in a lot of stop and go city traffic?

Herblenny

03-18-2008, 06:50 PM

I don't drive slow.. but I'm usually around 3-5k RPM range on cruise. City vs HWY, I'm about 50/50.

I haven't checked my fuel filter.. Don't even know where it is:) I haven't searched it.

Tire pressure is about 30-32 range. And since TPS, I know if I go below 28.

Could it be that I need an ECU flash??

fikren

03-18-2008, 07:53 PM

here is a link that shows the mazda service bulletins. There is a new flash that came out this month I think but I'm not sure if it addresses anything regarding milage, but I have not read through what all the flash is supposed to be addressing.

http://www.finishlineperformance.com/store/pages.php?pageid=11

I'm assuming the Fuel filter is in the tank, I can't remember if there was a access hole in the trunk like the FD has when I had the carpet up doing the strut bar install, I assume there is though.

Other than that, you might want to check your air filter, map sensor, and o2 sensor. I would say if any of those are bad it would have an adverse affect on your mpg.

I also came across lots of information about the 2004 rx8's haveing worse mpg than the newer models. Something about when the cars hit the united states the emissons didn't pass so the fix was to bump up richness or something to that effect, however I would assume that flashes past that point over the years would have addressed this issue with the 04's.

It seems with the complicated air/fuel ratio system the rx8 uses, that if you are doing steady driving (long distance highway at constant speeds), the map sensor is able to get consistant readings that are not changing much therefore the fuel economy seems to be better on a long distance drive where as with mixed driving the consensus is that fuel economy is worse based on the fact that your not getting readings that are staying in one spot but rather jumping up and down so the car is constantly readjusting the mix which can lead to a lower mpg.

I would think something is definatly off in your car though Phil, if you have just recently noticed lower mpg than previously.

I8U

03-18-2008, 08:38 PM

I haven't checked my fuel filter.. Don't even know where it is:) I haven't searched it.

Well, you might as well give up on the fuel filter...it's a combo piece part of the fuel pump. If the filter is bad the whole assembly must be replaced...$297 if I remember from when I was quoted about 6 months ago. Besides anybody really looking for better MPG's in this car might as well trade it in and get a Civic. I normally average 11 mpg in town and anywhere from 18-27 on the highway depending on how spirited I drive. But it's a sports car, I really don't care about shelling out money on fuel. Phil, be happy you're getting the mileage you're getting...I've talked to others that are far worse even driving all highway.

Also, when traveling the highway try keep your rpm's below 3800, it helps greatly since the secondary injectors don't open up until then. I know that's right around 70mph, but it does conserve the fuel..

Herblenny

03-22-2008, 09:47 AM

Thanks guys Great info!!

Here is a quick FYI... I drove my MB FD to Nashville on Wednesday.. On my way up there I stopped for gas 2twice. After about 86 mile run I was averaging about 80MPH and filled up 3.6 gallons of gas.

From there to next gas station, I was averaging about 90+ MPH (with occasional 120+MPH pulls) and 117 Miles I filled up 6.2Gallons!!

Bottom line, I'm getting better MPG on my FD than my 8 :)

It took me 2hours and45 mins to go from Downtown Bham to Downtown Nashville with 2 stops.. I thought i did pretty good.

I8U

03-22-2008, 09:00 PM

Damn Phil...SLOW DOWN!!! No wonder your gas mileage sux! HAHA! Oh yeah, with the distance traveled at a normal speed in my 8 I could have driven there on less than 3/4 of a tank...and only taken me about 20 mins longer to get there...food for thought. :)

Now I'm not saying you didn't get good mileage because you did! Hell, on your 117 mile stint you averaged 18+ MPGs!!! Not bad.:icon_tup:

fikren

03-22-2008, 09:56 PM

Herblenny

03-24-2008, 07:06 PM

Another Update!!

I just went to ATL and just filled up!

I got 180 miles and put in 8.05 gallons! Thats about 22.22 mpg.

The trick was I went under 3800 RPM and set the cruise at 73MPH (RPM 3600-3700).

I8U

03-24-2008, 08:29 PM

Another Update!!
The trick was I went under 3800 RPM and set the cruise at 73MPH (RPM 3600-3700).

Hey Phil, I think I said that already...oh wait I did! HAHA!

Also, when traveling the highway try keep your rpm's below 3800, it helps greatly since the secondary injectors don't open up until then. I know that's right around 70mph, but it does conserve the fuel..

I8U

03-24-2008, 08:30 PM

There is no such thing as "normal speed" in a modified FD. :lol:

I know that's the truth...LOL!

ScreaminRX8

03-24-2008, 09:23 PM

Also, when traveling the highway try keep your rpm's below 3800, it helps greatly since the secondary injectors don't open up until then. I know that's right around 70mph, but it does conserve the fuel..

I went to Tampa last year, before I ever started pre-mixing and stayed around 70mph and averaged 23 mpg. with one fill up getting 26 mpg.<----had to be that damn contruction zone all the way through south Georgia 55 to 60 mph.

Herblenny

03-24-2008, 09:25 PM

Hey Phil, I think I said that already...oh wait I did! HAHA!

I know!! I'm not trying to take credit.. Just stating what I did:)

I8U

03-24-2008, 09:53 PM

Well, see you worried about your mileage and thought it was your car but really it's your lead foot you have to worry about. lol

I8U

03-24-2008, 09:56 PM

I went to Tampa last year, before I ever started pre-mixing and stayed around 70mph and averaged 23 mpg. with one fill up getting 26 mpg.<----had to be that damn contruction zone all the way through south Georgia 55 to 60 mph.

Last year when I went to Deal's Gap I averaged 26.2. Not too bad for my 6 hr drive there. Now once I got there that was different story...I was getting about 9mpg's , HAHA!

Herblenny

03-25-2008, 08:21 AM

Yep! Its my lead foot.. and I'm having hard time lighting that up... Maybe $5/gallon might help out:)

Within next month, I'll be picking up my sister's 4Runner. I might start daily that thing.. She says it gets 18+ on city.. I never thought I will be driving an SUV to save gas... LOL!

I8U

03-25-2008, 09:16 AM

Yeah that kinda goes against all logic! HAHA!

bop_rocco

03-26-2008, 12:26 PM

to all using the tc3 2cycle oil in the 8's can you use it in fd's? i picked up a bottle of castrol tc3 from wallmart but have not used it yet. I have been using marvel mystery oil but want to change to this if i can use it.

I8U

03-26-2008, 03:54 PM

^Hey man, 2-stroke is 2-stroke. I don't see a problem with using it.

Nexcis

04-28-2008, 01:02 PM

Have you guys been checking your spark plugs often to see if there's any extra carbon build up that wasn't there earlier. Also how's it affecting the catalytic converter I would assume that it would have a coat of soot from premixing. Please correct me if I'm wrong here.

I8U

05-03-2008, 12:11 AM

^Actually, I recently checked my plugs and haven't noticed any extra build up. And as far as the converter is concerned, no damage that I can tell.

Herblenny

06-02-2009, 08:50 AM

SPICcnmFD

06-02-2009, 09:09 AM

05rex8

06-02-2009, 07:14 PM

I wanted to bring this topic back up as I believe that my cause to get a new fuel pump/filter was due to pre-mix. I've also talked to one of the GA RX8 owner who tracks and he has stopped using pre-mix on his 8.. Similar reasons to why I stopped..

So, before you start using pre-mix on your Renesis, please think twice!! It costed me close to $500 to replace the pump assembly.
you could have cleaned the fuel pump sock or replaced the pump yourself for ~$125
it does help however to have the SST for removing the pump, but not needed :)

I would rather spend $125 or even the $500 you spent if it meant not having to buy a new motor due to lack of lubrication

Fidelity101

06-03-2009, 01:48 AM

mmo is more like seafoam meets ATF. I'm not sure if it can be run as premix, try it in your small engine 2 stroke if you got a weedwacker or lawn mower that takes premix.

Herblenny

06-03-2009, 06:07 AM

you could have cleaned the fuel pump sock or replaced the pump yourself for ~$125
it does help however to have the SST for removing the pump, but not needed :)

I would rather spend $125 or even the $500 you spent if it meant not having to buy a new motor due to lack of lubrication

I've heard that argument when I first bought my FD back 10 years ago.. People back then told me I should be pre mixing my FD... which I never did.. and I didn't loose my engine because of the wear.. And most I know either lost their engine due to bad tune (apex seal) or coolant failure. And for NA RX7, there are people who never pre mix'd go 200K.

If you look at the design of the Renesis, it already shoots in more oil than REW.. I'm sure more oil and premix might help lube the apex and side seals, but personally, I don't think it makes much difference but who knows.. But I think it does more damage when you might either detonate because less fuel is going thru or you get break up because your pump is no longer sending enough fuel.. When I first experienced problem with my 8.. It felt like I was having ignition issues.. Which I didn't know it was the pump until I took it to the dealership.. Hence why I didn't do that job.

Chibana

06-05-2009, 12:57 PM

There was a post over at another RX-8 forum that this issue is true when using many different kinds of oils that were not designed for pre-mixing in rotary powered cars. Idemitsu claims that fouling is common among people who use these oils, but that they have never heard of this issue happening with anyone using their pre-mix oil. Of course, they have a monetary reason to say that, but I also suspect it's true. I see an awful lot of people using ordinary two-stroke oil and such as premix, and it seems foolish to me. If you're going to do it, use one that's designed for the purpose, and has a lot of racing experience to back it up.

vex

06-05-2009, 02:17 PM

with regard to premixing, please see the oil discussion thread in the general rotary engine forum. There's appreciable wear when using premix oil on the wear surfaces.

SLOASFK

07-21-2009, 05:18 PM

So I get around 280 miles to the tank...is there something wrong with my 8? You guys seem to be getting more like 200 miles.

mfisher12

07-21-2009, 07:44 PM

I have an 86 N/A W/ the Racing beat true dual exhaust, K&N Intake, pineapple racing 5th and 6th port sleeves, light weight crank and alt pulleys, no A/C no P/S ( replaced w/ manual rack) and no air pump. I have never pre-mixed and I have 269825 original miles on the car. i get about 280 miles per tank and use 87 oct. and shift @ about 7,000 every shift (terrible but true, the injectors have been re-built more than the fuel filter has been replaced). the only thing i do is change the oil w/ castrol 10w/40 every 3 months or 3k and change the plugs every 30k or as needed.

may be just me but the best thing you can do is change your oil regularly and drive the piss out it! screw the gas mileage :)

mazdamaniac

07-22-2009, 02:52 PM

I wanted to bring this topic back up as I believe that my cause to get a new fuel pump/filter was due to pre-mix. I've also talked to one of the GA RX8 owner who tracks and he has stopped using pre-mix on his 8.. Similar reasons to why I stopped..

So, before you start using pre-mix on your Renesis, please think twice!! It costed me close to $500 to replace the pump assembly.

Pre-mix has no appreciable effect on your fuel pump. If anything, it will increase its lifespan.
The problem is the crappy Arram pump unit Mazda used in the fuel pump assembly.

You can read about this here:

http://rotarycarclub.com/rotary_forum/showthread.php?t=8540

I8U

07-25-2009, 03:04 PM

I have to agree with Jeff, the pump itself is crap. Probably why Mazda decided to go with Denso pump in the 09's...

therighthand

07-25-2009, 11:33 PM

Just saw this topic and thought I would chime in.

I think alot of what you guys are seeing isn't because of premix itself but rather because of the various types of Premixing you are using. You want to be making sure that injection type premix is used for injection applications and mix in fuel types are used once again in the proper application.

If you want to have no way of going wrong Motul 710 is the was to go!