let me throw this out again :

MAzda Knows BeSST We KnoW NOTHING! NOTHING! NOOOOTTTTINNNGGG !

 

hey man, did you really have to insult my intelligence to make your point

Of course I know what it means to run an engine with totally worn out bearings - i've learned that lesson the hard way with piston engines in the past.

BTW, you do know that newer engines (not talking about rotaries only) have even tighter bearing tolerances that allow different oil grades - meaning - 'thinner.' (sorry, I had to!!!!!!)

I am not convinced - yet - that abnormal bearing wear is the leading cause of engine failures in the RX-8.

At the end, both MPG and oil debates continue to be holy wars on this forum and any other car forum I visit for that matter.

 

My commute is 50km one way. I seem to actually burn more fuel doing 100km/hr than I do at 120km/hr highway, though I haven't had the chance to actually measure the milage. As with most vehicles, I find the rx-8's fuel gague drops an extra notch after I shut it off and turn it back on to go home, but that might just be me

 

What is this chart telling me?

All I see is that on road trips I get 19+ and daily driving 15ish.
All 19+ peaks are road trips!

 

I can get 24mpg on the highway if I shut off all accessories and keep the windows closed and drive on a flat road with the cruise-control on. In real life, I could probably get above 22mpg on the highway in the spring if the weather where I live didn't turn hotter than Satan's anus the instant the gas stations switch to summer gas.

The primary determining factor in gas mileage is engine load. More Newton-Meters of torque sustained for the same length of time will require burning more gas -- with the sole exception of significant changes in engine efficiency at different RPMs. If the engine is significantly more efficient at converting combustion heat to torque at 4500rpm vs 3000rpm, then it is *possible* the gas mileage might be the same at 85mph vs 55mph, despite the extra torque required to push the car through the air faster.

However, that seems like too big a difference to be plausible to me. More likely, whoever invented that myth prefers to drive at 85mph, so their driving is smooth at 85mph, but twitchy and aggressive at 55mph. I notice a significant improvement in gas mileage when I use the cruise control, because it keeps me from wasting energy speeding up and slowing down and gunning the engine to pass people, so that seems like a more likely explanation for the origin of the myth.

 

Don't forget changes in altitude and prevailing winds. I always notice better gas mileage on long trips when my destination is at a lower altitude than my origin. Just being able to coast longer when slowing down makes a big difference on a several-hour drive.

 

You know to be honest I understand where hes coming from. Reason being, I have a 30 minute highway drive to my old school which i visit frequently. I also have about a 25 minute drive to work which is relatively stop/go, not too crazy stop go though, just about 5-6 lights.

Anyways, I find that I burn WAY more gas on the highway drives than I do going back and forth to work. I actually sometimes burn 1/4 tank going 30 minutes to the school and 30 minutes back, and its all highway. My speed varies from about 65-75. On the drives to work though, its much less costly.

I know that sounds very strange, but that is what I have noticed. I wanted to post this odd experience I have been having, and this seems like a pretty decent place to paste it.

 

My personal anecdotal evidence says having driven >70k miles in my 07, I alway got the best mileage at > 70mph rather than 55mph.


I've always used the garden-variety oil, 5W-30 or sometimes 5W-40, filter, and absolutely no pre-mix. I don't always uses 91 octane gasoline; I alternate 87-89-91. Currently at 70k miles + , and never any "issues" including flooding; though I do redline every other drive. My 8 has never been to a shop or dealership except for the initial recall for ecu reflash.

The stuff I read here at the forum seem all "myth" to me. Thus, I never had the inclination to register.

 

Don't get me wrong dude. we are friends ~

all 13B engine use the same Rotor Bearing, exactly means that hasn't been change for the past 30 something years.

and e-shaft is the same too except it has an extra hole drilled out for that extra 0.6 lbs of weight saving over the last one. and yes it works with ALL 13B engines.

so I'm not so exactly sure why you think it's "tighter"

I know some company saids you should check bearing clearance when using it, but so does all older Rotary engines ~~~ it's not just Renesis engines suddenly have tighter clearance. That's exactly the reason why Mazda actually sells different "size" of rotor bearing, just in case you need them for whatever reasons. same idea as the Spacer, 90% of the engines are ok with the "V" spacer(and for Renesis, it's "C" spacer I think), but they also have 5 or was it 6 other different sizes so just in case you have some "weird" problems, you can find something that fits.

the major problem with Renesis is They underestimate the heat generated from the side exhaust ports, when exhaust fume gotta take a 90 degree turn to get out, it will be out "slower", excessive heat build up there will kill the seals it sees the most ---- side seals. Out of spec Rotor Bearing (worn out) will put even more stress to every hard seal in the engine, it might not be the direct cause, but when it's out of spec ... well you get the idea.

 

Mazda used a "better" ECU in 06-08 version, and yours is a 07, it's newer, so you will suffer less damage compare to say, 04-05-06. that's the reason why they did the updates to newer cars first, to minimized the damage.

I can tell you my engine went from regular compression to failed in 9 months --- if I remember correctly, when they test it the first time I had premix in it, but before the 2nd test, I stopped using premix about 2 tanks before hand, and the test came back as failed. so it's probably the premix that kept it "passing the test" before.

just telling you that your butt dyno is not a good way to tell if your engine is healthy.

You don't have to believe anything, it's your choice, but when it fails, unless something broke into pieces, you will not notice.

 

this is not true. the 1968-1991 engines all use the same bearings and clearances, but the FD uses different bearings, and uses a tighter clearance.

the high power Rx8 uses the same bearings as the FD, but it again uses some difference clearances, and the 04-08 cars use different oil pressure too.

Mazda actually had Idemitsu do an oil study for the Lemans engine in 1991, so actually the oil debate is settled, its fairly black and white what works in a rotary and what doesn't.

they found that in a racing engine, running a lighter oil = gains in efficiency, but it does wear more. they chose a 50 weight oil for the race car, but the race car had to cover something like 3,000miles at wide open throttle. so the duty cycle on the race car and a street car are totally different.

in a street car you could run a thinner oil and get the efficiency benefits, without encountering the wear that they would see in the race car.

 

Bingo.

 

this is from the paper. they chose the 3rd one from the top for Lemans, however Lemans is something like 3000miles @full throttle, which is totally different than a street car. also they have some margin in there in case the oil gets hot, there is another graph of basically oil overheating temp, and they chose the one that let them run it the hottest. test engines were single rotor R26B's

again, since this is linked to engine load, on the street its much less important, as the 13B-MSP makes less hp than the R26B (per rotor), and on the street its hard to see full throttle for more than 15 seconds.

on the street the 4th one down looks good, 2.6% efficiency gain, with trace wear, and hey this is what they choose for the Rx8.... obviously if you take the 8 to the track (and you should), a 40 weight oil would be more appropriate.





mike

 

haha, it's all good man. No hurt feelings

Although I am not 100% sure on the specific measurement of the clearances, I still would like to challenge your assumption. I've read somewhere the clearances are not the same for all rotaries. But again, that's info I read a while ago on an article while searching the web.

If that info is correct, then I stand clear on my aforementioned statement!!

 

Ultra Gauge (after calibrated) says 1 to 2 MPG difference between 55 and 80 (24 to 22). That is not much. On my Expedition, that difference is like 20 to 15.

8 was not always that way. I recently changed the fuel pump, MPG went up about 2 across the board, a little more at highway speeds, my guess is better fuel atomization with correct pressure.

Cruise Control messes with the throttle a lot. If you leave it for a bit, engine leans a bit and you get better mpg. Learn to drive steady.

 

I just finished a 1000 mile round trip to Michigan's upper peninsula. In the lower peninsula, I was cruising at 75 and got 23 mpg. Once in the upper peninsula, the speeds dropped to 60 and got an average of 25.2 over three fill ups. The tank was filled completely each time, and distance was divided by gallons to calculate milage. This was running 91 or 93 octane. Only time I have ever seen anything above 22. My wife couldn't understand why I was so excited.

I had just tracked my car two days before. No idea if this helped at all or not, but it was the only thing out of the ordinary.

Also, there are a few rare stations in the U.P. which carry ethanol free 93 octane. I didn't think it would make much difference, but suddenly the car just came alive. I had never felt it pull so hard. Or maybe it was just placebo effect, but it sure felt fast. Now I'm on a mission to find a local supply.

 

FD and FE uses the same size of Rotor Bearings.

N3A2-11-B11
N3A3-11-B11

they don't use the Yellow bearings anymore on FE cuz I think it will be too loose?

Same thing for Stationary Gear

NF01-10-E04
NF01-10-E05
NF01-10-E06
NF01-10-E07
NF01-10-E08
NF01-10-E22
NF01-10-E23
NF01-10-E24
NF01-10-E25
NF01-10-E26

as for FC, FD bearings are known to work (Mazda said it too) with it and same thing for all prior 13B.

yep, lower oil pressure + 5w20 = bearings eaten up. it's proven fact.

the 13B-MSP might not make as much torque (NA baby ~ ) but it also suffers from low oil pressure from factory, just like the FC. there is an oil thread(yeah , I know -_-) that talks about it and almost everybody (except me, I'm still under engine warranty lol) there swap the oil pressure regulator with a higher rated one and couldn't be happier. Remember people on FC (me included) also use FD regulator and have no problems.

Wrong, does not apply to 13B-MSP at least, there are wear using 5w20 engines, not so much on 5w30 (and up).

remember the study was done 20 years ago and things might look a bit "different" now.

Oil technology did improved over the years(a lot), but there is a limit. Cars with 5w30 does show less wear than cars using 5w20. I mean yea every car is different (drivers, how it driven,etc) but this engine (Renesis/13B-MSP) is the highest output NA engine, and seriously, Mazda is really pushing it, 232 hp ... and I wouldn't be surprised if they missed a few things here and there in their "studies"

and sometimes just because they did a study it does not mean they found all the issues, when you compare S1 and S2, you will know the stuff we talk about here(most) were right.

- Fuel pump is pathetic
- 2 Oil nozzle pointing at corners
- OMP rate is too low
- Lack of oil pressure, result in bearing wear AND OMP nozzle clogging up
- 1 oil cooler on AT? seriously?
- etc

"study" can tell us a few things, but I think real world owners is the only one who can find bugs for the manufacture so they can fix them

One good example is the Hyunda Sonata Hybrid that I bought, there was a serious bug in their software in the Hybrid ECU that will just stop working altogether under certain conditions, I mean it will just STOP working/moving altogether out of nowhere, there were people diving it on the highway and it just stopped working ... the car just died with the nice "HYBRID SYSTEM ERROR" message ... I'm sure Hyundai did their "studies" in labs like 50 million times. but it was found by owners and they fly out engineers all over the country to fight the problem and issued a fix in a month.

Forgot to add, if 5w20 is good enough, then you really gotta explain why Mazda recommend 5w30 all over the world except North America ? not like our 5w20 have magic dust in it. and friends over in Japan (also Rotary freak) said they don't have much engine failures over there, and most are over 100K without much issue.

 

i know you can put FD bearings into an FC, but it wasn't that way from the factory. also some of the difference is in the cut on the Eshaft, the FD and Rx8 engines have more clearance at the rear of the rear main journal.

Hyundai sucks. when i worked there we had this "smart stock" system. we had a new dealership with no sales history, but somehow we had every part we needed to fix every warranty problem. so since they knew what parts to stock, they knew what was going to break... think about that for a second.

we run 5w-20 in America cause we have CAFE standards to meet.

 

so which one is it? Are bearings/clearances different or not?

 

I drove to Mackinaw City (290 miles) this summer cruise at 78, 2 passengers and camping gear, A/C on... 23.5 mpg. I am documenting all fuel mileage in Excel... guess I got a good one lol

 

it wasn't like that from factory because ... well a lot has changed since 1985(first FC) to 1991(First FD)

they updated the part and it is ok to use either of them.

as for the rear main journal, some people said it doesn't line up but I have had no problems matching it, fits perfect. so I dunno -__-

at least they are willing to fix whatever problem they have.

They know what's gonna break, is it a good or bad thing? well think of it this way, most Mazda dealers have no idea how to fix a problem IF IT'S NOT IN THE FSM. is that a good thing ? even when they call the "tech line", they STILL can't fix some of the problems.

point is, some owners here said Mazda said it's ok to use it so it must be ok. they think Mazda's words = Bible. Well, for some of the stuff maybe. but when it comes to oil weight, not so much.

 

there are different bearings "sizes", it depends on what you wanna use (or what you have to use)

too tight, not good,
too loose, not good

FE shares the same bearings as FD. and it is ok to use FD bearings in FC and even older 13B engines.

Think of their side seals, they are smoking crack when they said its ok to have 0.06 clearance. when everyone do 0.02 some even go for 0.

point is, if you follow the FSM, it will be ok most of the time (FSM can be wrong too) but it's never the best.

 

The Renesis doesn't use the same stationary gears as the FD. The stationary gears in the Renesis have asymmetically-profiled teeth to reduce gear noise.

 

Well, I just did a ~2500 mile trip this last week. It seemed to do a bit better around 77 or so. I think keeping it under 80 (4,000 rpm) keeps the secondary port closed. That said, I was cruising through Texas at 90 average or so, and still got about 21 mpg. I was doing some hyper miling techniques a bit though, so it kind of worked out.

But for the most part, I got the same with mixed driving as highway. About 21 average. Doesn't matter much if I baby or redline it a good bit. Maybe 1-2 mpg difference.

 

more than 1/2 the stuff on 13B-MSP is backward compatible with prior 13Bs ...

Bearing is the same. gear has different part number BUT it's usable. just like other 13B parts.