ssneakster

So my car can't get over 21mpg and I've never owned a car I couldn't beat the rated highway mpg rating in. I've noticed it won't use top gear (or maybe it's just torque converter not locking up) until the car has been driven for about 15 minutes in a mix of city/highway.

I checked the thermostat in hot water and it opens at 180°. Is the tranny using it's own sensors to monitor temperature or is it based off of engine temp?

The other issue is the brake and battery light coming on. I've replaced the alternator with an aftermarket unit and now when the vehicle is warm I get the warning lights. My obd2 scanner wouldn't give me the voltage so I haven't been able to see what it's doing while I'm driving.

Any suggestions to shut off the warning lights or get acceptable fuel mileage? (24mpg+ with premium driven like a grandma). Bad Maf? Water control valve? A/T temp sensor?

Thanks in advance for any advice you can spare.

Cotozic

The car's A/T has to warm up with about a 10 minute drive before it starts functioning 100%. That is completely normal. Temp is based off Engine temp. 180 is a normal half gauge read. My car normals sits between 185-200 degress F.

Do you have any SES codes? EVAP system in order? Are you carrying a lot of weight? How are your tires?

maxinout93

like cotozic said, what gas are you using? check tire pressure, and its normal for the transmission not to go into the last gear/ overdrive when its cold until it warms up. Air filters plugs also check or replace if you havent.

ssneakster

Plugs, filter, and tires are good. I usually run like 40 psi to try and get some fuel mileage out of this thing. I was running shell v-power 91 octane on the last tank that got me 21 mpg.

My 88 Supra with a 3 litre was heavier and still got 10 l/100km, maxima is at over 11 l/100km with taller gearing and higher compression.

foodmanry

iTrader: (15)

To be honest a car that old and getting a little less than the EPA MPG is normal. You are chasing pennies with dollars at this point.

Focus on fixing your warning light problem. What kind of alternator did you use? Did you replace it with a re-manufactured alternator? A number of org members have had issues with replacement alternators from aftermarket auto places. In some cases it take two or three alternators to get one that functions.

You may have to pull the alternator and get it bench tested. How is your battery? Even with a new alternator a bad battery can give you those warning lights.

Juan M. Marroquin

My Maxima gets 16.5 mpg. That's horrible compared to my buddy that has a Silverado 5.3 crew cab with a 3 inch lift and he gets 20 mpg.

ssneakster

The battery is only a year or so old so I doubt it's the issue. The fact that it only happens when warm makes me think the car isn't correctly telling the alternator how much charge to put out, assuming it's like Honda's Elextronic Load Detection system.

Some people are claiming like 28mpg on here. With the way I drive this car shouldn't be this bad. What are the symptoms of a bad/dirty MAF?

maxinout93

my i35 gets anywhere from 22 mpg to 21 mixed use driveing and it has a bigger engine than the 3.0, plus its not as good on gas as the 3.0 especially in overdrive. When i bought it, it was getting in the low 18s to 19s. So u def have a problem somewhere.

mclasser

You never said how many miles are on the car but an early sign of tired O2 sensors is poor mileage.

foodmanry

iTrader: (15)

A bad alternator can kill a good battery. I recommend getting both your alternator and battery tested. Do a search on here for charging system problems (a lot of people have had them) and you can get more information on the fuses, voltage regulator, and other troubleshooting. First thing is first, get those components tested (alternator and battery).

Good for them. You know most people don't know how to calculate MPG correctly? A lot of people say "I get 350 miles a tank" and guesstimate their mileage from it. Factory, brand new, 2001 Maxima MPG is 24 highway, 20 combined, and 17 city. This is for the auto. You really aren't that far off...again you are chasing pennies with dollars if you are going to spend a lot trying to get your MPG back up.

As I said before...focus on your battery light problem first and get the charging system taken care of. If you do this, you may actually find your MPG increases.

Donkeypunch

Ya that **** is funny.
I get 30mpg.
How do you calculate that?
I don't know, I figure it does though!

maxinout93

I guess they divide the amount of gas in the tank and reset the trip odo, and divide it like that.

Donkeypunch

How many miles per tank.

From full to where the light turns on how many miles?

Child_uv_KoRn

iTrader: (7)

You need a new maf or something like OP. That's attainable with all city and driving very aggressively.
Your buddy won't get 20 mpg with our 4 spd tranny LOL

As I've mentioned before, (spring '14) I achieved 24 mpg at 80-85 mph through the Appalachians (in WV) and 28 mpg at same speed through the rolling hills in a bone stock 2001. It's plenty easy to get 30 mpg if you're going 70, especially in Canadada :P

Juan M. Marroquin

My buddy does get 20 miles to the gallon. It's a flex fuel which shuts off cylinders unlike my car. That is why he gets 20 and I get 16.5.

ssneakster

The car has 195,000 km on it. I downloaded another app that lets me track the voltage. When cold the car charges at 14.4V as the car warms up the voltage drops to 14. After about 15 minutes the car is fully warm and the voltage drops to 13.8, the warning lights come on, and shortly after that the alternator stops putting out any power and voltage drops into the 11s. Is it overheating or something? Why is the maxima so picky about alternators?

ssneakster

I was running a full rad block, I've removed half of it to see if extra airflow to the alternator will make a difference.

Child_uv_KoRn

iTrader: (7)

He has a lot more torque, longer gearing and maybe even a 6 spd tranny (or cvt). Flex fuel means you can run stupid e85. If he had crappy gearing like our autos, then he would get **** mileage. I meant to say "our autos" instead of "4 spd" in previous post (edited now lol).

Driven aggressively that truck would drink a lot of gas. It has all the advantage for cruising minus aerodynamics.

You get bad fuel economy b/c you're not listening. You have a problem. Nor did you even read my actual mpg (tracked miles and gallons and used basic math oh no).

Juan M. Marroquin

I did read it actually. What's your problem with me? In every thread that I post in, you always have to post some smartass comment.

foodmanry

iTrader: (15)

Which is the correct way to calculate MPG. Fill up the tank, reset your trip ODO, and calculate based on miles to amount of gas needed for next fill up.

The tank method is for simpletons.

foodmanry

iTrader: (15)

Because of shi1ty electrical. It sounds like you need to get your alternator bench tested.

Not related to overheating or temperature fluctuations.

You may want to try checking and cleaning your ground connections.

ssneakster

I replaced the alternator with a Champion brand that had a similar issue (actually replaced it twice, first one had bearing noise, second one had the lights issue) they bench tested the second one and it checked out fine but I replaced it with another one from another manufacturer.

I read a post about somebody's radiator fan being bad and causing charging issues. Since it only happens after my car has warmed up that could be an issue. With half my rad unblocked today the lights didn't come on in my way to work, but did come on briefly near the end of my return trip home.

ssneakster

I might try removing the fuse for the rad fan and monitor my coolant temps via obd port. If the fan was shorting out it would explain the voltage dropping into the 11s.

ssneakster

Well it turned out to be a bad voltage regulator. My alternator tested fine but I had the regulator replaced anyways and so far so good. It was a Pure Energy alternator from Rockauto. Don't ever waste your time with one.