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Discussion Starter #1 (Edited)
I know I mentioned this awhile back when I hit 30K, but I've blamed it off on one thing or another for quite some time. This weekend the nail was driven into the coffin as I took a trip I've done many times before and clocked a fantastic... 33MPG for the trip. In the past that has been anywhere from 37-40 at the same speeds sustained. Is this possibly buildup on the valves over time? (TPMS has been being stupid, but tire pressures are 36PSI cold in all 4, checking every morning).
On my daily drive I had been returning (and griping about mind you) 32-33 (down from 35-36)... now more recently down to 29-30. Again, I've been finding excuses to write it off... but is it time to bring this up to the dealership service and see about having the valves checked for build-up and a general run down of other things?

Rest assured, I want to blame my own driving habits as well, but the other cars haven't taken a sudden slump in MPG they're both as good as ever clocking in 31-32 in the miata and 24-26 in the formula on trips. (a good portion of the trip I reference above in fact..)


Update 1 (Post techron additive):
I'm not far into the first fill after the additive, but so far performance hasn't dropped from the tank WITH the additive, and MPG is up back around 34MPG average so far this tank. That's a near 5MPG (re)gain indicated so far.. but I'm only 100 miles in, so we shall see :)
If this holds up, it's safe to say the valve timing definitely allows for valve cleaning, and a little boost every now and then with something like the techron/seafoam/etc wouldn't be a bad idea. For this to be effective, fuel must get to the top side of the valve, thus the concern of it not working at all on a DI engine.

Update 2 - 4 tanks in
Back down to averaging around 32MPG... still driving 80/20 hwy/city...

update 3 - Long trip fuel mileage still down, but up from what it had been.
To expand on that a bit, I recently took a trip I've done a couple other times when the car was new to the tune of 39-41MPG averages. This last time I got 36, and ended at 33 for the tank... vs typically ending with 39 on the tank. I think "blah" sums it up pretty well. At least gas is cheap again :/
 

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Discussion Starter #7
you guys seem to mis-understand what I've asked. This has not happened just since the switch to winter blends. This has been an on-going continuously detrimental problem. My last trip in the same conditions was also in winter with ambient temps in the 40s-50s with winter fuels... (roughly same time of the year). My gas mileage has been on a down-trend since 30K about.. (4 months ago?). I'm not grumbling about a 3-4MPG drop, this is nearly a 10MPG drop, in the same conditions on the same trip. As I said, I understand changes do occur, and I've been writing off the down-trending MPG for quite some time...

As for a couple of the other factors, car is still 100% stock and alignment noted as within spec at least OCI/inspection - 32K miles... oh yes.. fresh oil change too 2K miles on it, that's never been enough to adversely affect MPG before on it's own, usually detriment begins around 6-7K.

Dis-regard warm-up times to some affect.. this was 4 hours of driving non-stop. (on the particular shoved me over the edge crap MPG returned at least).
Again, overall I'm down 5MPG ON AVERAGE vs last year per my records.
 

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Discussion Starter #8
Get the service manual, pull the intake manifold and look at the intake valves for yourself...and take photos if there is carbon buildup. Mazda says that valve overlap prevents this, but I'm not sold given other people saying they have benefited from sea foam cleaner.

Also do direct injectors ever need to be cleaned? I know somebody else here said their car benefitted from some injection cleaner.

Also are you running a slippery oil like the factory oil? Not all 0-20s are created equal.

Freakish of all, you could check the engine compression to make sure there isn't an issue with combustion chamber sealing.

There's some points I hadn't really thought of.. I do normally run chevron cleaner every few tanks.. I've avoided that with this car, as I thought it was a complete waste. Maybe I shouldn't have? I also thought the same on sea-foam with a DI car, perhaps that's needed as well, but most comparisons using it even as often as every 5K, by 30K there is still crud on the valves.


Compression... If anything the car has more pep now more than EVER. If it's down on compression and performing better.. so be it, LOL.
 

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Discussion Starter #10
10mpg is a 20-25% decline.

Something's wrong with the vehicle; I'd check for a drag sources (e.g. a dragging brake caliper) for starters.

My last 4 tanks have been down a few mpg but I've had a bike carrier on the back with bikes on it -- and that hits me for ~3-4mpg at 75mph. Drag matters, especially at highway speeds!
Hadn't thought of that ticker, thanks. I haven't noticed any dragging sounds, or anything overtly obvious hanging down (where I park it's usually obvious). However, I WILL take a quick look under/around the car for anything that sticks out that could be causing a problem! (would be quite fun to call the dealer griping about MPG to find a splash guard somewhere has come loose -.-)
 

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Discussion Starter #13 (Edited)
Also yes, Using just 87 octane when the weather got colder. After 50* ambient it's not worth the added fuel cost IMO.. but 70+ it's an easy choice to use premium. Brakes feel to be working well, and there is no excess wear on any one rotor... I will double check the free-play though to be certain..

I also got my best MPG's around 20-25K miles ticker.. held steady to about 30K and it's been downhill ever so slightly ever since. Much like you I hit 41+ MPG on a trip to myrtle beach. Wound up with 39.6 calculated out for the trip after a day of city driving to finish off the tank (50 miles out of the 620) as you can imagine a lot of that city driving was sitting, lol.
 

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Discussion Starter #18
Over the past few weeks, I've noticed a considerable drop in mpgs, from about 37mpg down to 32mpg. I don't remember having this drop in mpgs in my 2014, but then again I didn't have to drive that much. My commute has changed from a 20 mile round trip to a 60 mile round trip due to a move a 5 weeks ago.
that sounds more in line with what I've been experiencing, lol. It's not a happy thing... but at least it's not JUST me.. :/ With yours being newer too, that makes me feel a little better about it, I think....
 

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Discussion Starter #20
you do realize I'm talking about getting 5-6MPG less than I got in the same/similiar conditions last year vs this year? I think a lot of people are missing that point...
My normal winter drop for this car was 2 MPG.
How many times has that been said now?!
 

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Discussion Starter #22
Quite correct, beskhu. I've checked everything external to the engine except alignment, and that'll be done in a couple of weeks when I get new tires. After that I'll worry about tearing into the intake, lol.
 

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Discussion Starter #26
Thanks S100Y. I'll grab up a bottle of the Chevron cleaner and see if it helps mixed with a tank of premium. I had thought with the DI it would make no difference, but apparently something with the valve timing allows some fuel to get over the valve for cleaning on certain cycles occasionally, lol.
Hopefully it will help. Just took another 200 mile trip and chimed in at 33 for the trip... one that use to ring in at 38+ easily. (I.E. not trying and not putting around at 60-65) Now even trying - 33. -.-
 

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Discussion Starter #27
Wear and tear, tire wear, alignment, winter time, brake wear. All effect that mpg. My post was more of a statement that I don't think anything I physically wrong, but the car has alot more wear on it now then it did last year. It's not outrageous to see that drop in mpg at 30k+, a good de carb service would help at that mileage. If you know a friend that works at a dealership see if they can hook you up and do one for you. Or else you are looking to spend 160-200. On a real good de-carb service. The additives work overtime, but by the time they do work you spend as much as the de-carb service.
Gotchya, that makes more sense, lol. That's what I was thinking along the lines with the intake cleaning and such. I know on some brands it's regular maint. at around 30K.
 

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Discussion Starter #32
Well, we shall soon find out. I just went in DEAD EMPTY, dumped in the BIG bottle of techron.. filled with 5.2 gallons of gas. Smells like race fuel.. NICE. Let's see if it does anything to help aside from make my nose hairs tingle....
 

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Discussion Starter #33
might I just add... I wish the car acted like this all the time. It LOVES octane o_O... less effort to accelerate, better throttle response, little more torque a LOT sooner. ECU is aggressive little monster on this thing. That really makes me curious about what's actually acceptable to expect from a tune without eliminating the efficiency in the early cycles.
Ah well, I digress. So far according to the instant MPG, I'm getting better MPG in the same places I usually glance at it. Avg is up a bit as well, and that's not even being fair because the new throttle response has been teazing me.

(on a ramp I normally barely get to 75 on with all of us in the car.. 85 without hitting full throttle as early as I normally do!)..
*disclaimer* I do NOT recommend doing this. If you do so and blow up your engine I'm not responsible, LOL.

even after the drive to work the exhaust still had a noticeable "smell" to it. At this point I'm not 100% sure if it's an octane smell or a smell from cleaning soot and carbon off of the top of the valves. DEFINITELY seeing more white smoke than normal on AWUS starts
 

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Discussion Starter #36 (Edited)
That's like taking 3 days prescription meds on a single day!! I don't know if the ECU is programmed to handle so much octane, hope it does'nt do anything bad. I went exactly by the instructions, 1 bottle followed by 14 gallons of 87 gas.
Basically.. LOL.

It's not the first time I've done that, usually on motorcycles that I can't get the time to tear down and clean the throttle bodies on properly. Works magic. I was a little worried about the car with it's timing advance and compression to be honest, but it's handled it AMAZINGLY. (but if a 1L 160HP motorcycle can with 13:1 compression.. well.. surely.)

As I said, I don't recommend it to others :p


Solar, I agree. LOL. This was the truck dose for 22 gallons of treatment even, hah. Even my wife made a comment about the smell of the exhaust. o_O

So far Hwy MPG is SINGIFICANTLY improved... but, hard to judge anything on this tank. I would be afraid to see the AFR at highway lean cruise right now!!!
 

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Discussion Starter #37
bump,

I'm not far into the first fill after the additive, but so far performance hasn't dropped from the tank WITH the additive, and MPG is up back around 34MPG average so far this tank. That's a near 5MPG (re)gain indicated so far.. but I'm only 100 miles in, so we shall see
If this holds up, it's safe to say the valve timing definitely allows for valve cleaning, and a little boost every now and then with something like the techron/seafoam/etc wouldn't be a bad idea. For this to be effective, fuel must get to the top side of the valve, thus the concern of it not working at all on a DI engine.

Also added to OP for ease of reading. :)

FWIW, I opted to go with 92 octane for this tank just to ensure things are cleaned out, and hopefully KEEP it that way. As noted before, I've normally LOST MPG with premium, so these gains so far are very impressive IMO.
Loosened up (or tightened up as the case may be) with less buildup on the valves FTW! :D
I'll be opting for a full top-end cleaning and media blasting of the valves at 50K (BMW regular maint.) if I still have this car at that point.
 

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Discussion Starter #42
yes.. it appears so. A partially fouled injector with 35K on the clock? seriously? o_O. I honestly wouldn't have even thought of it. Makes sense though.. and seems a LOT more plausible than a major valve cleaning from this little extravaganza. But it's not like I just putz around in this thing either, why would it have a partially fouled injector already? Heck My other car is still running OEM Injectors at 130K at 105% duty cycle at WOT, and they're doing just fine o_O I honestly never even question injector integrity at the age of this car... Maybe I should?
 

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Discussion Starter #45
Probably due to bad gas...are you regularly pumping non-top tier fuels?
pumping the same stuff I put in the "other" cars... BP/pilot/loves. The only difference is regular vs premium. Even then, shouldn't the fuel filter take care of anything that would potentially clog an injector this early in life?


Honestly performance is significantly better than it's been for quite some time. That same on-ramp I always have brought up isn't giving me any trouble at all (I can hit 85 by the end of it with a bit of ease now vs before.)
 

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Discussion Starter #48 (Edited)
thanks solar. I'll mention it. They're a really good bunch, so I know if I brought it up they would take care of it. As I mentioned though, I really didn't want to take the car in because "MPG is bad now!". I think even they would laugh me out of the garage for that one, lol. So I wanted to try a few things first to confirm :). This definitely has. I'm at 34MPG 200 miles into this tank now holding steady. That's normal for this time of year for me.

As for the fuel filter... I don't know? That's a thought for sure.. if the answer is no I may be looking into that route.




Besh, I checked the aero panels first as ticker recommended early in the thread, all good under the car. How many miles did your 6 have? I went through a period of REALLY REALLY weird steering feel at about 25K and it sorted out by 30K and the car feels good again. Also I'm due for a set of tires at 36K (buying next week in fact), and that certainly contributes some to those factors.


As for 36K.. turned to my wife this morning at 35914... "Anything you want me to get checked? Last chance on bumper to bumper, LOL"


Honestly.. with bumper to bumper toast, and a few random misc issues here and there that never really got 100% solved (rear seals sticking again, trunk still sticks, MPG taking a dump and being cured, steering felt wavy earlier and resolved itself with a few thousand miles, wind noise is still as annoying as ever with all procedures applied to all 4 doors).. I'm going to be looking hard for a nice low mile CX-7, or something similiar. I'm trying my best not to, as paying this car off is fast approaching, and I could get another really nice toy if I just suck it up. But I don't wanna... LOL.

Who would've thought performance wouldn't be on that list? hah. She feels great right now though, even has *decent* passing power at 2,500RPM now *shrug*
 

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Discussion Starter #52
I had a huge list of unresolved problems (axles, brake rotors, wind noise, engine startup noise, bushings, strut noises, clunks and bangs, trunk latch busted, throttle issues, power loss, horrible fuel mileage, seat heaters not working - the list goes on), partially due to the dealership... "car feels fine, nothing wrong" and due to the fact I live a ways away and had a hard time continually hassling them (better things to do).

An all time high of about 39mpg with ease to struggling to get 26 and no immediate recourse?

It was a relief to unload this one, sorry forum!!
That sounds terribly familiar.. unfortunately so. I mean, I'm glad the techron additive resolved my MPG and power issue, but to have so much of it so soon?

The CX7 we owned before is a more fair example I can give. I put ~50K miles on it from 24K-75K when we sold it. Direct injected turbo, and was practically 21MPG the entire time we owned it (2 years) *shrug*. Note there that in the same 2 years I put MORE miles on it, and had no problems AT ALL. Again using primarily BP and pilot fuels in it. (love's is pretty new to my area, lol)
 

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Discussion Starter #55
Racing Tiger, If I was in your shoes I would, despite your other cars never having problem with Pilot and BP gas, still make a new habit of filling up at a different subset of gas stations for the Mazda 6. If the problem happens again you will be able to completely rule out the brand/type of gas causing the problem.

Also, you should try "racing" your wife in the miata while on 93 octane again, perhaps you would be able to keep up now that your injectors are clean?
That I don't have much doubt about solar. 93, clean injectors, and this cold cold air right now, the 6 is rather peppy. It will still lose, but nothing as bad as the first time playing around. the on ramp where 80 was a struggle is now 85 with all of us in the car and a breeze with just me. Not the 120+ the formy cracks off, but pretty good for a daily family hauler. lol
 

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Discussion Starter #64
definitely run the techron and a few tanks of premium oc cc. I made the same run up to nashville this weekend that I did a few weeks ago (and posted this thread). I returned 36 on the way up, and dropped to about 35 by the time I got home (80-85 the whole way home.. I was sick of driving *shrug*) So my MPG is right back where it should be.... I would expect better, but with winter time, and tires due for replacement AND it's time for my next maintenance (37K) this coming week. I'll take it, because that's a LOT stacked against those #'s.

P.S. Injector cleaning definitely wasn't part of the regular 30K... if it was techron would NOT have fixed my problem (that or it was crap built up on the valves), and mine was a premium full circle service at 30K....
 
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