Peculiar Gas Consumption @ 3k+ RPM

[mister_pond]

First of all, my bad if this has been posted before but I'm brand new to the forums and didn't find anything regarding this specific issue in the existing threads.

I recently bought a 2003 Protege5 from a private seller with 140,000 km, regular oil changes, etc. etc. My mechanic deemed it is in astounding condition for an '03. Lately however I've noticed my gas consumption spikes significantly when I drive over 3000 RPM and above - mainly highway. Anything under (including shifting) is perfectly fine. To give you some perspective, driving from my girlfriend's house to Toronto - 26 km highway, my I lost 3/8 of a tank. Driving that distance in the city wouldn't scratch a quarter.

My mechanic has looked at it before and can't find anything wrong. Any suggestions? This is my first Mazda, so is this normal?

 

[booboo0809]

Interesting. Overall, the car does drive at a very high rpm. At 3000 rpm you would be going like 110-120km/h? at least in my manual 5spd that how fast I go. However, that's no excuse to lose almost half a tank. I have no idea what the problem could be but i do think there is a problem somewhere? Its odd but you don't have any issues while driving in the city? maybe someone can enlighten you a little more!
good luck!

 

[mister_pond]

I would say that my speed is about 120 km/h at 3200 rpm. This is an automatic transmission - I probably should have mentioned that earlier. I'm taking it to another mechanic. Hopefully this one will have a better eye than my usual guy.

 

[i12drivemyMP5]

Mine is 03 sportauto with 95k miles and if I stay under 3k it'll still pull 30-31mpg, 410 miles per tank and 13 gal to refill & using the AC. Has done so regularly. However, if I sport it about and drive over 3k on frwy, which = over 70 mph & with AC, it'll dip down to as little as 24mpg. Haven't ever got worse than that tho. I have mods and full interior, nothing gutted.

 

[tweety2300]

24 mpg? I get 31 runing 85-90 mph

 

[i12drivemyMP5]

Is your MP3 automatic? Or as heavy as the P5?

My info directed at OP in a P5 with an automatic is that yes, the mpg can vary 6-8mpg no problem based on driving habits and somewhat more based on winter or summer gas or if ethanol mix or using AC or not. With all variables it isn't too peculiar.

 

[mister_pond]

My info directed at OP in a P5 with an automatic is that yes, the mpg can vary 6-8mpg no problem based on driving habits and somewhat more based on winter or summer gas or if ethanol mix or using AC or not. With all variables it isn't too peculiar.

I don't doubt the mpg will vary between drivers and specific vehicles, but should I be able to watch my gas gauge needle drop on the highway? I hope not! I've used my AC maybe twice this summer. Getting a cross breeze is fine for me.

 

[tweety2300]

Is your MP3 automatic? Or as heavy as the P5?

My info directed at OP in a P5 with an automatic is that yes, the mpg can vary 6-8mpg no problem based on driving habits and somewhat more based on winter or summer gas or if ethanol mix or using AC or not. With all variables it isn't too peculiar.

Thought the Autos did as good as manuals on highway? At that point it's just load and rpms. Auto or manual shouldn't vary that much should it?

 

[JiggaBro]

it ALL depends or driving habits.
i ONLY drive city, car is usually never on for more than 20 min. (usually around 8min.) and i drive it like i stole it. (never going more than 5mph over the limit)
and i have never gotten better than 19mpg (i once got 22mpg but that was with 50miles of freeway)

 

[i12drivemyMP5]

I don't doubt the mpg will vary between drivers and specific vehicles, but should I be able to watch my gas gauge needle drop on the highway? I hope not! I've used my AC maybe twice this summer. Getting a cross breeze is fine for me.

no you shouldn't be able to watch needle move. that would be craptacular mileage and or hole in tank or leak in line or injectors spewing type bad.

Thought the Autos did as good as manuals on highway? At that point it's just load and rpms. Auto or manual shouldn't vary that much should it?

maybe when torque converter is locked up in steady cruise but any fluctuations in terrain or accelerating to deal with traffic, not so much and getting to hwy speed should be noticeably better mpgwise in manual.

 

[stivine6]

Mine is auto 2001 with 227k km on it so far

i do mostly city driving and with a full tank i average about 400km-430km which isn't that great. I try to keep my rpms less then 3k but sometimes i go over.

 

[Bastian]

it ALL depends or driving habits.
i ONLY drive city, car is usually never on for more than 20 min. (usually around 8min.) and i drive it like i stole it. (never going more than 5mph over the limit)
and i have never gotten better than 19mpg (i once got 22mpg but that was with 50miles of freeway)

I deliver pizza in mine and regularly get 24~25 mpg... (boom05) hahah

 

[mister_pond]

I've been gathering a decent sample of my gas efficiency since my last post.

Before the ambient external temperature went below 7 degrees Celsius (I know there's a lot that affects the internal temperature of the vehicle and that's all way beyond me so bear with me):
City... 18 km/L (x 2.35 = 42.34 mpg) or 5.5 L/100 km
Hwy... 10 km/L (x 2.35 = 23.52 mpg) or 10 L/100 km

Of course what concerns me is the high consumption when I'm on the highway. Now that temperatures have gone below 7 degrees daily I don't touch the highway! Here's what I've recorded the last two weeks:
City... 10 km/L (x 2.35 = 23.52 mpg) or 10 L/100 km
Hwy... 7 km/L (x 2.35 = 16.47 mpg) or 14 L/100 km

My buddy who's a huge car enthusiast told me it may be the O2 Sensor and the MAF Sensor that is affecting my performance due to the previous owner's habits. Is this plausible? If not, do you have any suggestions?

 

[pcb]

I've got an 02 p5 manual and consistently get 37-39 mpg (12-14 km/L but I multiply by 2.82 to get our old school Imp. mpg. I always have to check whether or not the commercial is from Canada or the US when I see a new car is getting 58 mpg.) My mileage dropped down to 31 mpg so I changed the air filter and cleaned the MAF sensor (or maybe it's the MAS sensor,... the one in the intake tube anyway) and my mileage went right back to normal. My mileage wasn't temperature or rpm sensitive though so I don't know if that will help you or not. It's cheap and easy and should be done periodically anyway. Seafoam can't hurt either (at least I don't think it can) and there are how-to's for that,.. it's cheap and easy too. You might want to take a look at the input air temp. sensor in the air box when you clean your mas sensor and change your air filter. There is a test procedure outlined in the service manual for doing that. The service manual is a free download from one of the links in this site and it also lists other things to check when your mileage drops. P.S. I don't know how you ever got 18 km/L that's over 50 mpg in Canadian mpg.

 

[Fraya713]

Best I've gotten is 23 city. I think those spouting 28+ mileage are full of it or using creative math tbh.. but meh, i'm not the one driving their cars, what do i know.. still don't believe it

 

[pcb]

This guy say's he gets 50 mpg. I think I believe him,... he's obsessed. I get a kick out of what he's done. You should check out his thread.

http://www.mazdas247.com/forum/showthread.php?123812526-Protege5-Smarter-not-Harder!&highlight=

 

[rit14623]

I have an 02 auto trans P5. I can get a little over 33 MPG if I cruise highway at 55 MPH. If I drive 65 MPH, it drops down to around 28 MPG. If I drive 74 MPH, it drops to around 26 MPG.

I have a K&N air filter in the stock airbox which I clean around every 9,000 miles. I replaced the two O2 sensors at least a year ago. I've never achieved over 33 MPG.

I'll look into cleaning the MAF sensor. I've never cleaned it since I've owned the car, so that's like 100,000 miles. I don't know how dirty it is going to be but I keep the air filter cleaned. Anyone notice their MAF to be dirty?

 

[Installshield 2]

To touch on the differences between mileage at different sustained rpm...as it looks like you may have several different things effecting you.

the P5 ecu, manual or auto, goes from a very lean fuel mixture at low load and rpm (after warm-up) to a ridiculously rich one...its just how the closed and open loop protocols behave on these cars...the higher the rpm, the richer it gets (for a P5 ecu, anyway)...3100 rpm, iirc, is just about the switch position for these modes, but its not just rpm...its also load...so you can potentially get into 'rich' open loop at a lower rpm, and vice versa...and an automatic gearbox probably isn't helping, either.

Its been a while...but from what i remember an auto p5 loses an additional 10 or so whp over the same manual...no offense to your car, but 'cheap' automatic transaxles are notorious for sapping additional power from already under powered cars...but, this alone is not enough to give you that kind of mileage imo...

there are a few sensors you could have your mechanic look over...namely the IAT and MAF sensors, as well as the throttle position sensor...I'm guessing your o2 sensor(s) are perfectly fine, as they are only used in closed loop (which is the lower rpm range, and where you are getting great mileage)...

there is the off chance also that a water temp sensor is giving mixed readings...That thing on its own doesn't do a whole lot, as the dummy water temp gauge in the car is pretty much worthless...but the ecu does use this sensor to determine when the engine is properly warmed up, and then begins using closed loop for lower rpm and loads...

Sorry, wish i could help more...bad sensors are always annoying because they 'should' throw codes...but don't always do that. There is also a chance of the VTCS system getting stuck closed (possibly related to the water temp sensor as well), which is starving the engine for air...and requiring you to increase throttle position to make up for it...do you have to press the throttle and 'abnormal' amount to get the car moving? I know that is a loaded question considering these cars in stock form, and even worse considering you're new to the car...but this is a possibility i guess, although i've never seen it happen before...

just for reference...what does a auto run, rpm wise, at 70mph? I know i can get better mileage staying at 70 than at 75...but for my manual P5, 70 and lower doesn't make a noticeable difference...always right around 32...

 

[pcb]

When I cleaned my MAF it didn't appear dirty and no dirt seemed to run off. I understand that the K&N can release some oil that can contaminate the MAF, especially if you over oil it. I'm pretty sure it was my air filter that made all the difference. It's the first thing listed in the service manual for poor fuel economy under trouble shooting. It would make sense to me that a dirty air filter would have more of an impact at higher rpm due to the increased air demand. Sea foam may just clear up the problem then it doesn't matter what was causing it and you don't have to spend the money to find out.
Installshield 2,... I was wondering about my temp gauge,... It never seems to move except on it's way up to warm then it sits there ALL the time at just smidge under half way. Even when it gets hot enough for the fans to kick in the temp gauge does not move at all. Is this because of the temp sensor or it's placement or is the gauge reading what the ECU is telling it and not the actual reading from the sensor. I was also wondering if there is also a separate idiot light that goes off when it gets too hot or if the MIL light will flash or something. I had a heater hose fall off of my 85 626 and it over heated and warped the head in about 2 minutes and I didn't notice the temp gauge rising.

 

[Installshield 2]

Thats another topic, but the stock coolant temp gauge is worthless. From what i can tell, it has 4 settings...cold, warm up, 'normal', and overheated...I have yet to overheat (knock on wood)..but i've heard many reports that guys said it didn't budge until it was too late...

Annoying, as it definitely has warm up resolution...it doesn't just pop up to just under half way...it moves up as the engine warms...but guys have aftermarket temp gauges in where it will fluctuate between 190 degrees to up over 230...yet the factory gauge doesn't change at all...ridiculous, as 230 is well above 'normal', and a good 25 degrees hotter than where the fans will kick on if not moving...

I actually today ordered a oil temp gauge today for this exact reason, as i'm only getting higher and higher in mileage...I'm not sure where the stock coolant sensor is, but i vaguely remember it being somewhere around the thermostat...ideally you need it on the hot side, opposite of the thermostat, before cooled by a radiator...as you want data on what is leaving the engine as soon as possible...but factory gauges almost never do that, as they also monitor radiator and thermostat performance as well...I'm only saying this as data loggers show the fans kicking on with a water temp of 204 degrees...that is most likely cooled already and about to enter the engine...hot side will give a higher number, but a better 'gauge' of engine condition in real time...there is some debate on that, but that is how i've always preferred it anyway, at least when you are only using one sensor in the system...and most aftermarket cooling systems will use a sensor before and after any heat ex changers, to better correlate with when to use the fans...