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So im out of ideas on my MPG. (Hate to make this thread)


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I feel like i have exhausted all options!!

 

I took her down to my shop, (they are alright, my last experience wasn't great, but nothing went wrong) and i had them check a couple of sensor's (mainly pre-cat O2's they said they were okay) and got the timing set.

 

Now, you may or may not know, i have been trying to figure out why i couldn't get my MPG over the 13 MPG mark. Everything that you would commonly expect to go, is new, or not in need of replacement. New dizzy cap, and rotor. NGK spark plug wires and NGK spark plugs, engine air filter, mobile 1 full synthetic full flushed through. new knock sensor, with OEM intake manifolds. throttle body cleaned, TPS set, idle is good (ish) O2's are good. The only things im aware of, are a leaking exhaust manifold. and a few unrelated suspension issues.

 

But, my shop told me that my engine "wouldn't get up to temperature". It never exceeded 180º during his test drive. I didn't give it a second thought, because he said that until the computer sees a pre-program engine temperature value, it will keep dumping fuel, till it reaches that set value.

 

It made really good sense to me, and im sure that's very true for a-lot of cars, if not the pathfinder. He recommended getting a new thermostat, and that made sense to me too, because i did my timing belt back in April, and my MPG issues kick in, around mid June. And i used a cheap, Stant thermostat, so maybe it had failed or started opening at the wrong temp.

 

I was ready to breath a sigh of relief that I finally found something that made sense, but out of curiosity, i went over to RockAuto.com (where i ordered my thermostat, among other things) and all of the thermostat temp ranges between 170º and 180º, and i have seen my running temp, through a bluetooth OBD2 reader, it reads between 179º and 186º. So i think its safe to say that my thermostat is working fine.

 

What the heck is left. here are my my mileage reports from as far back as i have.

 

 

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4/24 -5/1 was caused by timing being off, and on 12/22 i changed my knock sensor.

 

I know she can get 16 MPG, help me get her back up to that!!!

 

-Kyle

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You mentioned the leaking exhaust manifold, and that was a huge reason why I was at around 10mpg for a while. Mine had a crack in it, and after replacing it it was as if the heavens opened and I didnt need to make sure a gas station was within eyesight everywhere I drove. I'm no expert on the topic, but from my own experience, it made a difference to replace it.

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Based on what you've done so far(i.e. new plugs, wires, O2 sensors are good) my suggestion would be:

 

1. Check that exhaust manifold leak because if the O2 sensors read lean mixture (due to the leak) the computer will dump more fuel

2. Check your air-filter, replace it, they're cheap

3. Get yourself the 3M complete fuel system cleaning "kit" that comes in a box with three bottles. Run the fuel tank bottle with half tank of gas.

 

 

EF6B8D44-EAE4-4FE3-8EAA-49F8B95D1CCF-792

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Your thermostat is fine, it's supposed to fully open at 176F. How long does it take before it reaches that temp from a cold start?

 

Around 5-10 minutes of driving from a cold start, sooner if i let it warm up for a few minutes (i try to do this, but sometimes im just plain late).

 

You mentioned the leaking exhaust manifold, and that was a huge reason why I was at around 10mpg for a while. Mine had a crack in it, and after replacing it it was as if the heavens opened and I didnt need to make sure a gas station was within eyesight everywhere I drove. I'm no expert on the topic, but from my own experience, it made a difference to replace it.

 

hmmm you didn't change anything else in the process, that just seems too easy?

 

Just trying to see if this is my problem, before i go drop $3-400 on new manifolds. and then another $400 on a new exhaust (gonna do it all at once if its the manifold)

 

But that truely is the only thing really wrong with that engine.

 

I was told that the harmonic balancer is slipping (not oem, stripped my original one after doing the timing belt so many times with a crap tool)

 

That doesn't seem logical to cause this kind of problem.

 

And old (needing to be changed) trans/ transfer/ and diff fluid wouldn't cause this much of a drop either.

 

 

 

and Stioc and i have run 3 bottle of Chevron Techron fuel system cleaner, 3 bottles in a row at the recommendation of Towncivilian, no change.

 

 

Thanks for all of the suggestions guys, anything i can rule out, or explore further is very appreciated.

 

-Kyle

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Cold temperatures wreak havoc on mpg, also, because it takes longer for the engine to warm up and for the transmission fluid and gear oil to warm up, too. If you have an AT, the torque converter will slip longer until the ATF is warm.

 

Your records go back to April '12, while the weather was warmer. Have you been running the same wheels, tires, and drivetrain since April?

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If you don't already have M1 75W-90 gear oil in your differential(s) (or a synthetic 75W-90) I would suggest doing so at some point since synthetic gear oil will warm up quicker and not be as thick when things are cold, resulting in a very small MPG boost.

 

Leaking exhaust manifolds sounds like it could be causing problems as the replies above stated. You seemed to have already ruled everything else out that could be causing a massive MPG hit.

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"hmmm you didn't change anything else in the process, that just seems too easy?

 

Just trying to see if this is my problem, before i go drop $3-400 on new manifolds. and then another $400 on a new exhaust (gonna do it all at once if its the manifold)

 

But that truely is the only thing really wrong with that engine."

 

 

Yes, that was the only thing I replaced, and I got it from rockauto.com(http://www.rockauto.com/catalog/raframecatalog.php?ck[viewcurrency]=USD&ck[iD]=0&ck[idlist]=0) for $40-60. The first one I got ended up cracking as well when my exhaust got caught on a stump, and so rockauto actually warrantied it out for me and sent me a 2nd one free. As far as parts go, they've been really good to me.

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Exhaust manifolds aren't that expensive and you can potentially source a used one too- I wouldn't worry about the rest of the exhaust for now if it's not broken.

 

BTW, Techron is one thing the cleaning kit is another - it includes a spray for cleaning the throttle body as well as you to decarbonize the intake valves etc. I went from 16MPG to 19.2MPG (highway) with a new air filter and the 3M kit treatment- didn't touch anything else.

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Ya i would address the exhaust leak asap. I think i saw manifolds somewhere for 45ish per, i was thinking at the time, wow thats really not that bad. come to think of it i need to do mine. that will probably get me back up in the 19 range. after i did all the work on it i noticed when i started it up and the sea foam was filtering out of the engine that i had a BUNCH of smoke comming from the passanger side under the hood. so ya, seafoam helped me find me exhaust leak. i almost forgot about it till you said something. im gong to go see if i can order those real fast. i know the pita to doing that job will be getting those studs out without breaking them (if they r not broken already) have a good one, and i hope u get er figured out soon.

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http://www.partsgeek.com/gbproducts/DC/6750-05054936.html?utm_source=google&utm_medium=ff&utm_content=DN&utm_campaign=PartsGeek+Google+Base&utm_term=1996-2000+Nissan+Pathfinder+Exhaust+Manifold+Dorman+674-431+Left+96-00+Nissan+Exhaust+Manifold+1998+1997&fp=pp&gbm=a&gclid=CKuhn_eE7LQCFYLd4AodPkYA5g

 

Found the link to the manifolds, supposed to be redone by these guys to fix the failure points of the originals. I will order them and get em on in a few months when it warms up. not standing out there in this weather and fighting with rusty/broken bolts or studs. =)

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Exhaust leak, especially around the O2 sensor will cause horrible gas mileage, since the O2 sensor is saying way more oxygen than it should.

 

Also, you have very heavy wheels and tires. a 15x8 steelie... I can only imagine those weigh 10-20+ pounds more than the stock alloys. It takes more power to get those rolling, and that takes a toll on your mileage. Just something to consider.

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Posted 31 October 2012 - 11:39 PM

Your Pathfinder looks great and is in great shape for a 96. I want a spare tire hanger. Just think how cool it would look with a 4" lift.
The 31's are killing your gas mileage. Our 3.3L engines have 165hp and are geared for the tires stock. I have 31's on mine but the gear ratio was affected and caused power and gas mileage decreases for me, thinking of going back to 30's and/or gearing it. Larger tires make you tall geared and make the engine work harder in order to get up to torque curve, like starting out in 2nd and never being able to get to 5th unless on a downhill with the wind at your back sort of feeling.
Lifting your vehicle and running 30's gives you more articulation clearance in your fender well and dosen't affect your mileage and power very much, but sure dosen't look as cool as big tires. Let's say you were to run 37's on your Pathfinder without gearing properly, you probably couldn't get the thing rolling and would have no power and terrible gas mileage.
You get the picture now, if you get huge tires you need to gear accordingly or the motor can't push the tire circumference and negatively affects gas mileage and power band. Lifting the vehicle dosen't affect the mileage very much.
It's all cool just keep improving on it is my game.

 

Exhaust leak, especially around the O2 sensor will cause horrible gas mileage, since the O2 sensor is saying way more oxygen than it should.

 

Also, you have very heavy wheels and tires. a 15x8 steelie... I can only imagine those weigh 10-20+ pounds more than the stock alloys. It takes more power to get those rolling, and that takes a toll on your mileage. Just something to consider.

Edited by rocky2
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Exhaust manifold needs to be done. A crack in the throws your O2 sensor readings way off. I have a cracked one on the passenger side that I will be replacing ASAP.

 

I was thinking that wasn't it for the longest time, but then again, i only just started noticing the leak a few months ago (being able to hear it on start up)

 

Cold temperatures wreak havoc on mpg, also, because it takes longer for the engine to warm up and for the transmission fluid and gear oil to warm up, too. If you have an AT, the torque converter will slip longer until the ATF is warm.

 

Your records go back to April '12, while the weather was warmer. Have you been running the same wheels, tires, and drivetrain since April?

 

Thats true too, were getting a especially consistent cold winter this year, every morning when i start her up at 8:30 in the morning have been in the mid to high 20's recently. Usually winter in Washington is just a lot of muggyness and rain, lots of rain.

 

No i haven't been running the 31's since then, but i only went from a 30 X 9.5 to 31 X 10.5, while i agree with you and rocky2 in saying that bigger wheels and tires will decrease the mileage, but there is NO way that it can go from 16.3 MPG to 13.3 MPG. Also to prove that, i bought my duratrac's on October 12th, and you'll notice there is really no appreciable drop in the mileage i was already getting.

 

If you don't already have M1 75W-90 gear oil in your differential(s) (or a synthetic 75W-90) I would suggest doing so at some point since synthetic gear oil will warm up quicker and not be as thick when things are cold, resulting in a very small MPG boost.

 

Leaking exhaust manifolds sounds like it could be causing problems as the replies above stated. You seemed to have already ruled everything else out that could be causing a massive MPG hit.

 

Ugh, i keep forgetting to do that, oh and BTW i got a hold of Pablo, once i give the word, im going to meet up with him, happily, he's local.

 

 

 

Yes, that was the only thing I replaced, and I got it from rockauto.com(http://www.rockauto.com/catalog/raframecatalog.php?ck[viewcurrency]=USD&ck[iD]=0&ck[idlist]=0) for $40-60. The first one I got ended up cracking as well when my exhaust got caught on a stump, and so rockauto actually warrantied it out for me and sent me a 2nd one free. As far as parts go, they've been really good to me.

 

I'm kinda hesitant at buying aftermarket headers, but the price is so hard to resist. Hmmm decisions, decisions.

 

Exhaust manifolds aren't that expensive and you can potentially source a used one too- I wouldn't worry about the rest of the exhaust for now if it's not broken.

 

BTW, Techron is one thing the cleaning kit is another - it includes a spray for cleaning the throttle body as well as you to decarbonize the intake valves etc. I went from 16MPG to 19.2MPG (highway) with a new air filter and the 3M kit treatment- didn't touch anything else.

 

Good, point, i might look into that kit later. Every once and a while ill go back through my created topics and see if i missed or forgot about any suggestions.

 

Ya i would address the exhaust leak asap. I think i saw manifolds somewhere for 45ish per, i was thinking at the time, wow thats really not that bad. come to think of it i need to do mine. that will probably get me back up in the 19 range. after i did all the work on it i noticed when i started it up and the sea foam was filtering out of the engine that i had a BUNCH of smoke comming from the passanger side under the hood. so ya, seafoam helped me find me exhaust leak. i almost forgot about it till you said something. im gong to go see if i can order those real fast. i know the pita to doing that job will be getting those studs out without breaking them (if they r not broken already) have a good one, and i hope u get er figured out soon.

 

Thats awesome, Seafoam is very versatile.

 

 

Thanks again guys, i think we have figured out my problem, or at-least another thing to rule out.

 

I appreciate all of the advise.

 

-Kyle

Edited by ferrariowner123
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Kyle,

 

You said you switched from 30x9.50's to 31x10.50's on 10/12/12? Your MPG records indicate you haven't broken 14mpg since then, even though you were observing a downward trend in September

 

31x10.50's are 3% taller than your previous tires, so your MPG calculations will read 3% too low compared to your previous tires. Also, your new tires are 1" wider and likely have a more aggressive tread than the previous tires, which will increase the rolling resistance. Try running 35psi in front and 32psi in the rear. Running higher pressure than that will just wear out the center of your tread faster; your Pathy looks relatively stock.

 

I'm not saying the the only cause of your lower MPG is tires, but they definitely contribute more than you think.

 

Did you upgrade your wheels to the Rock Crawlers on 10/12/12 also? Steel wheels are usually heavier than aluminum wheels, and the different offset will cause the tires to stick out away from the body more, increasing drag.

 

Finally, did you put anything on your roof since the summer? When I first installed my safari roof rack, I observed an almost 2mpg decrease in mileage! It's amazing how much all the little things add up.

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I have a Scangauge II for monitoring lots of things on my truck especially intake and water temps, voltage etc but mpg tracking is a pain with it unless you always fill up the tank and never forget to enter the fillup in the scangauge. Maybe I need to RTFM lol

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I have a Scangauge II for monitoring lots of things on my truck especially intake and water temps, voltage etc but mpg tracking is a pain with it unless you always fill up the tank and never forget to enter the fillup in the scangauge. Maybe I need to RTFM lol

LOL. Using the SGII is a lot easier than manually entering mileage, gallons, etc. into a smartphone app! And the SGII tracks real-time fuel economy.

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Kyle,

 

You said you switched from 30x9.50's to 31x10.50's on 10/12/12? Your MPG records indicate you haven't broken 14mpg since then, even though you were observing a downward trend in September

 

31x10.50's are 3% taller than your previous tires, so your MPG calculations will read 3% too low compared to your previous tires. Also, your new tires are 1" wider and likely have a more aggressive tread than the previous tires, which will increase the rolling resistance. Try running 35psi in front and 32psi in the rear. Running higher pressure than that will just wear out the center of your tread faster; your Pathy looks relatively stock.

 

I'm not saying the the only cause of your lower MPG is tires, but they definitely contribute more than you think.

 

Did you upgrade your wheels to the Rock Crawlers on 10/12/12 also? Steel wheels are usually heavier than aluminum wheels, and the different offset will cause the tires to stick out away from the body more, increasing drag.

 

Finally, did you put anything on your roof since the summer? When I first installed my safari roof rack, I observed an almost 2mpg decrease in mileage! It's amazing how much all the little things add up.

Howdy guys, i see that a lot of you fellows r talkin bout the 31" tires. Im not sure what his had on it factory, but my 96 SE manual has 31's factory, and i was rockin the 19mpg for 4yrs since i owned the truck. unless he had the 30" package and a different gear set than mine, i would say it should probably have 31"s on it. Just a heads up on that. And 1" of tire shouldnt make that much difference in gear ratio. when u get to the 1:1 its like, 400rpm lower with the the 31" instead of the 30" so really not much at all. I do agree if you go BIG then ya. u need to regear, but 1" isnt really anything to worry bout. Just my 1/2 cent on the matter. have a good one guys.

 

PS im almost sure u wills see a big diff when u fix ur manifold.

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Howdy guys, i see that a lot of you fellows r talkin bout the 31" tires. Im not sure what his had on it factory, but my 96 SE manual has 31's factory, and i was rockin the 19mpg for 4yrs since i owned the truck. unless he had the 30" package and a different gear set than mine, i would say it should probably have 31"s on it. Just a heads up on that. And 1" of tire shouldnt make that much difference in gear ratio. when u get to the 1:1 its like, 400rpm lower with the the 31" instead of the 30" so really not much at all. I do agree if you go BIG then ya. u need to regear, but 1" isnt really anything to worry bout. Just my 1/2 cent on the matter. have a good one guys.

 

PS im almost sure u wills see a big diff when u fix ur manifold.

 

Yeah, I haven't noticed any difference in MPGs when I switched from 235/70/15 (27.95") to 265/70/15 (29.60"). :shrug:

I have an exhaust manifold leak too, but I don't think it's cracked. Probably the gasket or the studs. :popcorn:

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Yeah, I haven't noticed any difference in MPGs when I switched from 235/70/15 (27.95") to 265/70/15 (29.60"). :shrug:

I have an exhaust manifold leak too, but I don't think it's cracked. Probably the gasket or the studs. :popcorn:

You are still within acceptable gear ratio running (29.60) tires.

Oh, and it's cracked you can bet on it.

Check this site out on ring and pinion gears

http://www.angelfire.com/va2/nissan4x4/differentials.html

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You are still within acceptable gear ratio running (29.60) tires.

Oh, and it's cracked you can bet on it.

Check this site out on ring and pinion gears

http://www.angelfire.com/va2/nissan4x4/differentials.html

 

I shall bet you one US dollar. :beer:

Nice table. Didn't know angelfire still existed.

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Kyle,

 

You said you switched from 30x9.50's to 31x10.50's on 10/12/12? Your MPG records indicate you haven't broken 14mpg since then, even though you were observing a downward trend in September

 

31x10.50's are 3% taller than your previous tires, so your MPG calculations will read 3% too low compared to your previous tires. Also, your new tires are 1" wider and likely have a more aggressive tread than the previous tires, which will increase the rolling resistance. Try running 35psi in front and 32psi in the rear. Running higher pressure than that will just wear out the center of your tread faster; your Pathy looks relatively stock.

 

I'm not saying the the only cause of your lower MPG is tires, but they definitely contribute more than you think.

 

Did you upgrade your wheels to the Rock Crawlers on 10/12/12 also? Steel wheels are usually heavier than aluminum wheels, and the different offset will cause the tires to stick out away from the body more, increasing drag.

 

Finally, did you put anything on your roof since the summer? When I first installed my safari roof rack, I observed an almost 2mpg decrease in mileage! It's amazing how much all the little things add up.

 

While i do agree with your reasoning and proof, i still maintain that there is an exterior factor beyond where the rubber hits the road.

 

Even with your calculations, i should only see a %3-6 (ish) drop, not including for the wheels (which were installed a few months before, im getting to that), that would be no more than 1 MPG over all. The AMI (angular moment of inertia) would go up with wheels because there is a lower potential energy, so yes, the engine has to work harder.

 

But, a taller tire means, yes, the engine has to work (every so slightly harder) to get the car at speed, but with the dimensions at speed, the engine shouldn't have to work as hard to maintain, it, to the new gearing. so TECHNICALLY a taller tire means less rotations per mile. (to a point i know, but work with me here, were only talking a inch) But depending on how much city verse highway driving you will see different gains or losses.

 

Meaning, that between all of this new gearing, and weight malarkey i shouldn't see an overall loss of what im seeing now.

 

But to answer some of your other questions, i added the wheels on July 23rd.

 

I have ski racks on currently, cant say they have caused anything due the recent erratic MPG i've been getting

 

 

By the way, since you are keenly interested in fuel economy tracking, you might really like observing it (and other real-time sensor information) in real-time using a Scan-Gauge. I have one for my Pathy and one for my G37.
LOL. Using the SGII is a lot easier than manually entering mileage, gallons, etc. into a smartphone app! And the SGII tracks real-time fuel economy.

 

I'll look into it, im kinda digging having it on my Phone though, really handy.

 

Howdy guys, i see that a lot of you fellows r talkin bout the 31" tires. Im not sure what his had on it factory, but my 96 SE manual has 31's factory, and i was rockin the 19mpg for 4yrs since i owned the truck. unless he had the 30" package and a different gear set than mine, i would say it should probably have 31"s on it. Just a heads up on that. And 1" of tire shouldnt make that much difference in gear ratio. when u get to the 1:1 its like, 400rpm lower with the the 31" instead of the 30" so really not much at all. I do agree if you go BIG then ya. u need to regear, but 1" isnt really anything to worry bout. Just my 1/2 cent on the matter. have a good one guys.

 

PS im almost sure u wills see a big diff when u fix ur manifold.

 

Thank you, i have heard similar claims for guys like devonianwalk, he maintained his MPG after his lift, with manual hubs.

 

 

You are still within acceptable gear ratio running (29.60) tires.

Oh, and it's cracked you can bet on it.

Check this site out on ring and pinion gears

http://www.angelfire.com/va2/nissan4x4/differentials.html

I shall bet you one US dollar. :beer:

Nice table. Didn't know angelfire still existed.

 

So who gets the dollar? because i've seen my passenger side manifold and can tell it was cracked.

 

 

-Kyle

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