VQdriver

iTrader: (1)

hello. this is my second consecutive tank of bad mileage so it's not a fluke and i was wondering if anyone could help me with a diagnosis. the car is getting somewhere in the low 17mpg range in my normal commute when i usually get in the high 19s (NEVER below). the car has about 36k on the clock. this is what i've done with my car before it happened:
*4 slotted rotors, stainless lines, axxis ult. brake pads
*manual trans fluid change to redline mt90 (75w-90)
*rear diff fluid change to royal purple synth (75w-90)
*oil/filter change to german castrol 0w-30, fram extraguard filter
*2 bottles of chevron techron fuel system cleaner prior to above maintenace run to about 2 gals to empty followed by a new tank of fuel.

after about 15 searches i'm putting my money on the fuel system cleaner doing something to my injectors, sparks, or O2 sensors. i've also tried re-adjusting my ebrake to make sure they weren't dragging. also, the trans oil isn't the exact viscosity as nissan recommends. would it make such a profound difference in mileage? (btw mt90 sucks when the transmission has been sitting in cold 30deg weather overnight. car doesn't want to go from 1st-2nd for the first shift.)
i would actually think GC 0w-30 would improve my mileage but heard viscosity tends to be on the higher range. any thoughts? is there anything else i could do to check my work or the operating condition of the car? i'm probably going to run another tank or two before i start going back to oem fluids.

ZU L8R

iTrader: (84)

Stop using a fram oil filter. That has nothing to do with you MPG just an FYI. Check you plugs and your air filter. If your real concerned with MPG I'd spend $40 on a k&N drop in filter Also, check your tire pressures

VQdriver

iTrader: (1)

true, i realize that fram filters might be crap. i've seen the many threads on it, but parts have to be made to a certain standard, plus certain guys here actually do run fram and have highly built motors and all my domestic friends swear by it lol. i figure i could run it for the winter. i only bought it because GC was on sale at autozone. my next change is already sitting on the shelf: GC/k&n oil filter.
as far as the drop in filter is concerned, i forgot to mention i've had a K&N drop in filter for about a year now. no problems with that. the rest of the car is stock.
oh yes, i also tried unplugging the battery a few days after the maintenance to see if that would help. i'm not sure it did anything...so here i am. thanks

Motormouth

iTrader: (44)

tire pressure.

you are also going to have alot more viscosity from all of the new oils in your diff, trans and engine. that could be the loss as well.

maybe your rotors and pads are rubbing slightly from slim clearances...

a 2mpg loss at a normal 19mpg is a little over 10% loss. that does seem high.

ZU L8R

iTrader: (84)

Have you cleaned the filter since installing it?

Motormouth

iTrader: (44)

where have you been getting your gas from as well? what octane?

blastoff99

iTrader: (5)

It is possible that your local refineries have just now switched to "winter blend" gasoline. This will drop your fuel mileage.

Entaille

iTrader: (16)

my thoughts exactly. that would explain the mpg difference.

VQdriver

iTrader: (1)

tom! haha long time. how ya been?
i've been getting my gas from citgo and BP hear in C.H area. 93 of course. and i've always done that since day one. the car has never been below 19mpg. k&n air filter isn't too dirty, but still hasn't been cleaned. yea, i hope my pads aren't scrubbing. when i installed them i didn't see things out of the ordinary, but they did slightly touch because they're brand new.

i thought about winter blend gas for a second, but yet again the car has never been below 19mpg since day one and this started happening exactly after my maintenance. i'll add a few more psi to my tires and keep monitoring. sucks that there could be several factors to eliminate rather than just one.

Motormouth

iTrader: (44)

I am good, glad to see you still doing well Rudy.

it could be that cleaner. I have never used them though and that is total speculation on my part.

Master Shake

Someone on here also mentioned something about the air being colder now (or even too cold?). Seems strange to me, especially since people consider CAI's with long tubes, etc. But I do get 1 MPG less in the morning when it is 45 outside, compared to the drive home when it is in the 70's. Same route, same traffic levels.

Still not sure if there is anything to air temp being too cold for the engine!

Dealsgap

All of the above listed + ethanol. Depending upon where you get your gas and how much they are adding (anywhere from 1%-10%) this will effect gas milage...not only that but I just replaced all of my fuel injectors in my maxima. My mechanic said that he has noticed since ethanol has been added to just about 90% of the stations in my town that he has been replacing a lot of injectors lately..There are stations out there that are ethanol free you just have to search (web helps out also).

VQdriver

iTrader: (1)

yes, i'm guessing that too. i came up on a post where someone reported absolutely horrid gas mileage for a few tanks before it came back up. does that sound like affected plugs or o2 sensors? i've used redline fuel sytem cleaner in my old maxima with no ill effects. i decided upon chevron/techron because of reports it actually does something. tires are now up to 38psi (from 32) and i'll just wait it out to see if something good happens.

blastoff99

iTrader: (5)

38psi!!! There are things that can happen here, but I can't offhand think of any good ones. This sounds like an outright overinflation to me, and could negatively affect your traction and cause weird tire wear. Your search for that missing 2mpg could cost you more in the long run. Just my $.02.

VQdriver

iTrader: (1)

i def understand your concern. as far as street driving is concerned, i've always inflated to 38psi on this particular car. mind you, my G35C has the 19" sport package so recommended psi = 35. i'm coming from the subaru world where they inflate to 38-40psi+ on their 16" wrx wheels. i'm still on my first set of bridgestone RE050As and they have served me well wearing quite evenly. of course i have a set of dedicated winters to help save my summers. i actually think the +3 is a good safety margin for 19" wheels. just imo. i have to go to infiniti for an unrelated reason and i might ask them to check my A/F if possible. it's still under warranty.

Motormouth

iTrader: (44)

wtf are you talking about? did you mistakenly read his statement as like 83psi? are you dyslexic?

rotchcrocket04

iTrader: (12)

Wrong. 38psi is normal.


I'm willing to bet it's the fuel system treatment. Almost 100% of the time the following tank will drop reasonably more than a 2mpg loss. I used to run tests with another guy on another forum. I want to say the number we concluded with was something like an average of a 4mpg drop the following tank on 90% of the vehicles tested. I don't remember exactly though, was a long time ago.

Also, are you using the same fuel station? That can also make a big difference. I notice approximately a 2-3mpg drop between two stations around here (Hess and Wawa).

rotchcrocket04

iTrader: (12)

Also, I recently swapped my trans and rear diff fluids as well and didn't notice any difference in mpg. I really couldn't see how that could be affected by it.

On a side note, the Redline gear oil that I used in the trans is horrible on downshifts in the cold. It pretty much has to be forced into gear after sitting a long cold night. After it warms up, it's fine. I'm thinking about switching.

VQdriver

iTrader: (1)

i wish i ran up on your posts in my searches about fuel treatment. so, we're both guessing the same, could it be the plugs or O2 sensors being messed up by the clearing deposits? was it a permanent drop in mpg or did it return? should i run ONE more tank of the stuff or no? i've read about someone saying it took a few tanks for the mileage to return which is BS. i would have left well enough alone.

as far as redline MT90 is concerned, yes, it's horrible for me on the first shift in the morning. one thing i started doing was lightly winding the first gear to about 4,000rpm until i reach that first corner out of my development to get the gear oil circulating completely. i've done this for two days and the first 1-2shift has been nice and buttery since. i still want to change back lol.

anyway, this is a situation where i truly believe "if it ain't broke, don't fix it!"

blastoff99

iTrader: (5)

I stand corrected. Thanks for the info.