I was getting about 230-300miles a tank (15gals at every fill up I did), I was running 5W20, and then switched to 5W30 synthetic. Everything was the same for a good month or so, then temperature started dropping a bit here in Florida (low 70s) and hair became much more dry (w00t).

Suddenly my mileage has dropped to 100-150miles a tank (still 15gals at every fill up). I haven't changed my driving style at all.

I still shift whenever I get to the 4k-5k mark and keep it at roughly 3k RPMs. I also don't really go past 45mph, except for the short burst on the highway to 70mph, after which I put it into 6th.

I'm only at 4,500 miles, I keep the oil filled, and I haven't noticed a loss of power or anything of the sort, no engine light, engine still turns over just the same, I haven't noticed any fuel leaks.

So I'm rather confused. I still do the same 16 miles a day, of 10 miles city, 6 miles highway, and I haven't gained any weight.

I could take it to the dealer, but they're located 30miles from me, so it's a PITA.

Any ideas?

 

That's crazy man...I will post a reply but your situation is different. I've tested my vastly different mpg's I get but I noticed it has to do with my oil levels running 5w20.

If it gets low...my gas mileage drops to 13 and ****.

Seems yours is full though...if you are in warranty still...this is a legitimate issue.

 

My gas mileage has dropped also. I attributed it to the change to winter formulations of gasoline.

 

did you change to gas with ethanol? that dropped me by 2mile per gal

 

I get Premium gas (93 octane) at Sam's Club, rated at 10% or less Ethanol, but I've gotten gas from Shell and BP as well, and mileage was still the same. What's odd is that Dad's SUV is still getting the same mileage, and he gets gas at Sam's Club too.

It's starting to really bother me, but I'd rather avoid taking it to dealership if I can, they've been a bunch of asshats with my transmission problems in the recent past.

 

When it starts during the cooler days the choke is on longer, so it is a richer mixture for the first few minutes. That plus the winter gas is your problem.

 

So winter gas is different? I also keep it in the garage, which stays roughly 78F during the night, it always starts with only 1 of the redline extension bars, never both (unless I parked outside).

Ninja-Edit:

Read up a bit on winter gas, it has higher ethanol content, but to give me a near 50% drop though? O.o

 

Something sounds really wrong...even on my worst tanks I still get over 200 miles. And that's with all the f'ing around I do and 10 min warm ups since it's been ***** cold out. I don't know what to tell you man. But your car is definitely running rich.

 

Would resetting the ECU or something do anything?

 

my mpg is like **** no matter which season.

I think it has something to do with engine ... Cuz I used to get 180-200 per tank. but since last year I'd be lucky to even get 160 per tank. now its like 140 per tank

Im thinking, if Mazda dont wanna honor its engine warranty, I might have to use Geico's mechincal breakdown insurance coverage. Buy an engine from one of our forum vendors then have someone to install it locally. :o

 

How many miles are on your car? It might be possible that your coils got a problem... as far as I know, that will result in a drop of the gas mileage... but shouldn't be this drastic like yours. It is definitely not normal. The car effectively uses twice the amount of gas.
Such a drop can not be attributed to winter gasoline or the temperature difference... which is not even that big in your case. Nothing like real winter conditions.
Did you notice anything in the way the car runs, or everything is exactly the same as it was except for the gas mileage?

 

^What he said

There isn't a gasoline that the car will actually still run on that will halve your normal MPG. Something else is going on. The car seems to run like normal in terms of smoothness and performance?

 

were u premixing? HAve you ever? are u sure u have no leaks because that much of a drop it has to b going somewhere other than the motor i dont' see ur motor using that much no matter what even if it was bad...I think u betetr check everything out again..but i still recommend taking it to the dealer and see if they see anything

 

I'm at 4,300 to be exact. It runs exactly the same as before, it's still responsive, quick, handling is the same powerband is the same, speed remains the same.

Yep, as smooth as always, same performance

Never premixed.

I've checked for leaks multiple times, had a friend drive behind me for 30mins at 15mph around his neighborhood, hitting stop signs and stuff, no leaks were seen to drip onto the road, I've run my hands over the underside, nothing felt wet.

 

might want to replace your thermostat- if its sticks the car stays in open loop longer. you can attribute up to about a 30% drop to winter gas. the rest is indeed a mechanical issue.

 

^oh sh*t I forgot abut the thermostat yeah taht is a good possibility I always overlook the thermostat!!!

 

Put a camera up where you park your car and see if somebody is siphoning your gas

Honestly, no idea. If she's still running good, and hasn't thrown any codes, the only thing it could really be to see that drastic of a change would be a bad (but still functional) front O2 sensor, but that doesn't seem very likely.

 

I doubt someone is siphoning the gas since you need to pop open the cover, plus it's in the garage, so I doubt they'd go to the trouble of opening my garage and then the fuel cover when my Dad's SUV sits outside

The thermostat like the one that shows on the dash? If so, it's not stuck.

Or is it a different one?

Thanks guys

 

There's nothing wrong with your car.

You only drive 16 miles per day. That's only 8 miles one way.

Now that it's cooler, your car takes longer to warm up. Rotaries are horribly inefficient when they're cold. You're spending too much time in the inefficient engine temps, so overall your mileage is suffering.

Tell you what. Go drive a full tank of gas-worth of driving this weekend (take a day trip and have some fun). You'll find your mileage is back to what is was before; the longer you drive the engine when it's warmed up, the better mileage you're going to have.

My winter mileage drops to about 15 mpg from 20 mpg, because I've only got a 12 mile one-way trip to work every day, and it takes almost 5 of those miles before the engine is fully warmed up.

 

Ah, sorry, forgot to say I do about 250 miles every weekend when I go to Miami (100 both ways, and roughly 50miles inside of Miami), and I gotta fill up three times otherwise I won't have gas on Monday

 

to all you spoiled people.. I'm lucky if I get 200 miles to the tank.

 

so you are getting the same 150-60 miles on a tank while driving to and around miami?

 

People, keep in mind that the "colder" temperatures he's talking about is low 70's high 60's The engine not warming up as fast is not the issue. It has nothing to do with the ambient temperature, and I doubt it has much to do with the "winter gas" either. Even in the worst conditions 10 MPG is far below "normal."

It's under warranty, I would take it to a dealer if you have one nearby that doesn't suck (fat chance, right?). Something is wrong. I'm really surprised it still runs well and hasn't thrown any codes... are you sure it isn't leaking somewhere? It should be pretty easy to smell if it is.

 

i've only owned my car for a couple months now and the most i've recorded was 220 out of a tank.

anything i should look at that the previous owner might have missed? the car has 46,XXX miles on it

 

Hm, Im usually getting 225 miles before I fill up. And thats with 12.5 to 13 gallons.

Since you have an 09, you SHOULD be under warranty. Take it back to the dealer .. and let them solve it.