my mileage is going down the tubes. over the course of the past few weeks, i went from ~330 miles per tank to ~260 miles per tank, with about even mix of city/highway driving. i was at ~23 mpg and this past tank, all highway, was at 16.142 mpg. serious drop in efficiency. i've changed the oil, and i've removed my oscai. mileage went back up about 1-2 mpg after the oil change but now it's really bad again. oscai made no difference.
the only event i can think of within that time period is a flat tire. the sidewall on my driver's side rear tire blew and it tore the rubber cover off of what i thought was the emergency brake line. now i'm thinking it may have been the fuel line.
i'm no mechanic by any means, so let me run this by you guys. i'm thinking if that was the fuel line, does the pressure in that line increase with speed? wot? that would explain why there's no fuel on the ground when it's sitting still. any peripheral leakage would just evaporate pretty quickly anyways.
could it be anything not related to the flat? maybe a bum fuel pump? seals? i have no idea. i'd like a pretty good idea before bringing the dealer into the picture.
any suggestions/ideas are appreciated. i need a way to fix cuz i'm afraid this a prelude to something catastrophic.

 

also, i'm in southern california, which is basically at sea level and super hot... does it matter? would heat cause this kind of change?

 

Have you tried leaving the battery disconnected overnight to see if a good brain washing addresses the problem?

If you think you have a fuel leak, you can check under the car every morning/day, or place some time of tarp under there to inspect any "droppings".

The warmer weather could have an impact, but not as great as you describe.

Have you changed gasoline or service station you attend? Has the heat gotten to your brain, which makes you drive harder? How many miles do you have on your car? I have noticed my mileage increase with more miles on my car...

 

lucky bastard
i'm at 36600 miles in one year. high mileage. i'll try the battery thing tomorrow, along with yet another oil change.
thanks mdeal

 

Did you try asking your nissan dealer? It's worth a try, they seem to be pretty knowledgable about their cars

 

yeah. went to buena park nissan and got slammed repeatedly by the service guy for trying to get them to look at it. i swear i've never met someone so condescending. i just left there with him in mid-sentence and tried out another dealer, but they were technically clueless.
i'm thinking maybe i'll have a local mechanic check the fuel line pressure and just eat the cost. i cannot stand nissan service. they blow. i'll need a pretty good idea of what's going on before i go back to a dealer again.

 

Well, if it makes you feel any better, last week I got 16.44, down from my average of about 21.5. (I too, have seen my gas mileage go up about 2mpg from break-in.)

Mine was due to long idling with the A/C on *constantly* (avg 90-95degF) in humid, sweltering heat.

You don't mention a few things.

How do you measure your gas mileage? You need to completely fill your tank each time. If you estimated by a mark on your gas gauge, your mileage will fluctuate wildly.

Did your area recently go to oxygenated fuels? (i.e. MTBE or Ethanol?) If so, that could account for some of your mileage.

Did you accidentally fill with 87 octane instead of 91-93? That could do it too.

Do you smell gas in or around your car? If you do, don't use a lighter to find the source... Oh, also, mdeal's tarp suggestion may not work if you're not dripping gas (i.e. vapor leak), or the leak only occurs when the fuel systems is fully pressurized. The nose works best.

Got any friends that play practical jokes? In a movie (I think it was a movie) there were these guys that kept putting a gallon or two of gas in this guys car, without telling him. He thought he was getting like 50mpg, and bragged to everyone. The perps then started to siphon gas out...

 

1 - tank is full. i mean SUPER full each fill up.
2 - i have no idea if we're on oxygenated fuels. i'm in fullerton, california if anyone knows. what effect would it have?
3 - no 87 octane. even if i used it accidently, i don't think i would have made that mistake 3 three weeks running.

 

the keyword is seem my friend...

 

Other suggestions: 1) Change your brand of gasoline and see if the situation improves--make sure its a name brand; 2) Run a couple of fuel injector treatments through your fuel system. Chevron's Techron product is very good, cheap, and readily available. BG 44K is a better treatment, but its more expensive and only available at auto repair centers.

 

Be carefull with this one. Did you know if you overfill your tank, the vapor recovery system the gas stations use will suck gas out of your tank and back into their system?

Quote:

2 - i have no idea if we're on oxygenated fuels. i'm in fullerton, california if anyone knows. what effect would it have?

If you're near a large popluation center, you're probably on oxygenated gas. The amount varies depending on how far away you are from the population center.

We're forced (by the corn lobby) to use ethanol here. Ethanol has less energy per volume than gas, and raises the octane rating. So, instead of getting a better gas with fewer volatile compounds, we get gas that's partially octane enhanced with ethanol, and has less power per volume unit. I've found this also translates into about 1-2mpg.

I'm not sure if the same is true with MTBE. (However, if the environmentalists weren't the one's pushing for oxygenated gasolines, we'd *really* be hearing about the groundwater contamination that MTBE causes...)

Quote:

3 - no 87 octane. even if i used it accidently, i don't think i would have made that mistake 3 three weeks running.

Always the same gas station? Just because the label says premium, there are plenty of shady operators...

 

maybe an oxygen sensor went bad or is going bad?????

 

This I agree with. Try something else to see if it affects your milage

This I DON'T agree with. In the manual (take it for what Nissan says) states specifically NOT to use any fuel additives. Whether is to boost the money in their pocket or it has a true reason I cannot tell.

When you drained the oil the first time, did it look/smell/seem any different than it normaly does. Does the oil smell like gas? I found it interesting that your mileage went up when you did the oil change, but you also changed your oscai as well. I would be curious to find out which one gave you the mileage.

I was suffering mileage problems, but I found out it was because I was "topping" off everyweek (with good gas prices) and driving very little (less than 100 a week because I ride my motorcycle)

I took the car on a trip and went through the entire take ans suffered poor gas mileage. I then filled up with same gas (different station) and experienced much better mileage. The difference was about 4 m.p.g. An idea only, because if you have greater than 36K in one year, I am assuming that you drain the tank in between fills.

You were going to change the oil again...let us know what difference that makes

 

thanks for the input guys.
i don't change my own oil so i don't know the condition of the used oil. but i went and got another oil change today from a different lube shop. i'll have to wait and see how this tank turns out.
as for the gas, with all the driving i do, it's pretty rare that i use the same station too often.

 

What's MTBE? I've seen stickers on gas station pumps all over...is it bad for the car?

 

Methyl tert-butyl ether. It's an oxygenate used in fuel, in some places (i.e. all of California) a mandatory adjunct to gasoline. Oxygenated fuels generally lead to cleaner emissions from cars.

In the last five years MTBE has drawn considerable attention as an environmental pollutant, particularly as a ground water contaminant. I'm unaware whether it's bad for engines.

 

If y'all see any independent studies that support this, I'd like a link. Studies from the EPA, ADM, the corn lobby, etc. (i.e. those with a vested interest in having the additives put in) don't count.

The reports I've read show that there was only a *miniscule* to *no* effect by the additives. By no means is there any sort of cost justification for the oxygenates. 'Course, it's the government that's forcing this, and they're here to help you.

Quote:

In the last five years MTBE has drawn considerable attention as an environmental pollutant, particularly as a ground water contaminant. I'm unaware whether it's bad for engines.

If you had an old car, ethanol would have several effects:

1) It would remove all the rust from your gas tank/lines. While this sounds okay, you'd be changing fuel filters every couple of weeks for the next year.

2) The alcohol would attack the seals in the car, sometimes will very ill effects.

3) The acids formed from the alcohol combustion would eat away at cast iron manifolds, causing premature failure in the exhaust system.

But hey, it's all in the name of cleaner air, right? (Oh, and filling the farmer's pocket's too. Can't forget that.)

 

You might be right. This is a complex issue:

...while the benefits of reformulated gasoline for automotive emissions has been clearly demonstrated, it is not clear that the presence of MTBE as a component of RFG contributes significantly to the overall air quality
benefits.

http://tsrtp.ucdavis.edu/mtberpt/

 

what's with ur sig ??

taken in NM ?

U'r showing that premium is 90 octane ??

 

Is this in the high desert? Lower octane gas is sold at the higher altitude locations, usually above 5,000 ft or more above sea level. This is an adjustment for the thinner air, so its not a long term problem with high performance engines. Try driving above 8,000 ft w/o a turbo or a S/C though--its an experience.

 

hmmm...my friend works at Buena Park Nissan. but since he's a sales rep, i never checked out their service department.
try Connell Nissan in Costa Mesa, 405 Freeway off Harbor.
i've let them service my car their for few times and they were actually one of the few dealers i've come to appreciate.
they have very nice service reps and the machanics there were very knowledgable. once a mechanic even offered me an advice on how to build go-fast Maxima~!
anywayz...36,000 miles in one year surpasses me. i had 34,000 miles in my first year. now at 50,000. so i've cut down on driving alot this year(only(?) 16,000 in 8 month!), but my fuel mileage hasn't been affected greatly. i'm still averaging about 20-22 mpg, but that's also because i'm running 2 fuel pressure regulator set at 40psi.

 

Yes, this was taken at a gas station near Los Alamos, elevation >1 mile.That explains why my Mercury Sable rental had no guts!

 

Been there, done that.

You don't even need to go to 8K. Try driving a Denver rush hour. The local residents are used to only having 75-80% of their engine.

Not me. I felt like I had to flog the car to keep up with their insane style of driving. If I lived there, I'd definately have a pressurized engine.

 

thanks irvine78, i've been in search of a decent service dept. they don't even have to be racing freaks, just so long as they're stand up guys. i'll try them next weekend for sure.
anyone in particular in service i should ask for?