# Loss of fuel economy



## silvertank (May 26, 2015)

Lost about 4 to 5 mpg since last oil change . Started off about 2mpg average and has been increasing slowly since, brought it up to the dealer and they told me nothing they can really do about it as its super hard to diagnose but to test the oil when i change it again and let them know if anything abnormal shows up. gonna change he oil this week and up date to see whats going on my average mpg stays pegged around 30 now instead of around 39 to 42. Im averaging 37 to 39 where i was averaging 41 to 42 calculated by each fill up. Anyone got any idea it should have went up not down


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## newsguy99 (May 24, 2013)

my LT/RS gets right at 30 mpg, no matter what. Highest I've seen is 32 mpg.. And thats at the pump, not with the DIC.


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## IndyDiesel (May 24, 2015)

silvertank said:


> Lost about 4 to 5 mpg since last oil change . Started off about 2mpg average and has been increasing slowly since, brought it up to the dealer and they told me nothing they can really do about it as its super hard to diagnose but to test the oil when i change it again and let them know if anything abnormal shows up. gonna change he oil this week and up date to see whats going on my average mpg stays pegged around 30 now instead of around 39 to 42. Im averaging 37 to 39 where i was averaging 41 to 42 calculated by each fill up. Anyone got any idea it should have went up not down


Do you know if your CTD is having short regen cycles? If it is that will effect mpg big time.


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## silvertank (May 26, 2015)

IndyDiesel said:


> Do you know if your CTD is having short regen cycles? If it is that will effect mpg big time.


No idea, how would i go about checking that i checked dpf pressure and it was spiking around 200 220 psi 


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## Snipesy (Dec 7, 2015)

You don't unless you have one of those scan gauges. Or the dealer tools...

Probably end up being a wild goose chase. It could be the... Air filter, MAF sensor, MAP sensor, fuel rail leak, clogged dpf, bad fuel, bad fuel filter, not meeting fuel pressure, bad egr valve, bad egr cooler, bad throttle valve, low tire pressure, worn injectors, exhaust leak, intake leak, bad dpf pressure sensor, bad egts, just to name a few.


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## silvertank (May 26, 2015)

I had a scan guage but was causeing massive feedback and tons of error codes, everything looked good and no codes but seems like it i also have less power


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## Snipesy (Dec 7, 2015)

Massive feedback? Explain.


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## silvertank (May 26, 2015)

Causeing error codes from esp malfuntion to loss of power steering and engine and transmission codes, removed it and they all went away


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## Snipesy (Dec 7, 2015)

Yeah that's pretty bad. Reset it somehow or get it RMAed. It's doing something it's not suppose to.


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## silvertank (May 26, 2015)

I sent it back ill buy another soon as i get this issue figured out with the fuel economy


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## ChevyGuy (Dec 13, 2014)

silvertank said:


> I had a scan guage but was causeing massive feedback and tons of error codes, everything looked good and no codes but seems like it i also have less power


What brand? From what I understand, most can deal with the Diesel Cruze. In fact, I think that's a special order item for the one brand that does support it.


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## silvertank (May 26, 2015)

It was scan tool . Net mx bluetooth scanner 


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## silvertank (May 26, 2015)

Worked great for a week then messed up 


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## Snipesy (Dec 7, 2015)

Oh I thought you meant the actual scan gauge. You can try to make it not refresh as quickly. Disable anything that rhymes with fast.... Not sure though.


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## silvertank (May 26, 2015)

I may try that with my next one


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## LulzT1 (Aug 24, 2015)

Those cheap Chinese bluetooth/wifi plug-in adapters have been known to cause all sorts of crazy issues, especially with newer cars. They make adapters that allow you to open/close windows just as an example of what they are able to control in your car when plugged in (there are complaints the device opened windows by itself, not good if it rains lol). Also, the wifi one I have has an LED that will drain the battery within a week if left plugged in.

I highly recommend getting a SC2 as several members have here including myself. There's a firmware version tailored to this car. I have torque pro as well and I don't think the diesel PIDs are correct for this car. No way the dpf is under 200psi, that would be crazy back pressure for the motor to overcome, should be more like 5-15psi range give or take. Then you'll have access to # of completed regens and when it's occurring. It's worth every penny.

As for the OP, have you changed driving habits at all? More summer traffic? Tire pressures? With the hot weather in the northeast I know have been cranking the a/c full blast. You previously mentioned using B20, have you switched back to straight diesel? I don't think an oil change would affect mileage unless they put molasses in there..


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## silvertank (May 26, 2015)

Driving habits have been pretty much the same other than ac route is the same i used both or a blend depends whose cheaper usually a minor difference in the economy, no real traffic 


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## silvertank (May 26, 2015)

Are you talking about the scanguage 2?


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## IndyDiesel (May 24, 2015)

silvertank said:


> Are you talking about the scanguage 2?
> 
> 
> Sent from my iPhone using Tapatalk


YES....That is where I would start...I have the Scanguage 2 and have to ask for it to be configured for the Cruze Diesel. Its about $150


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## silvertank (May 26, 2015)

Who did you get it through?


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## IndyDiesel (May 24, 2015)

silvertank said:


> Who did you get it through?
> 
> 
> Sent from my iPhone using Tapatalk


ScanGauge - Trip Computer + Digitial Gauges + ScanTools, get a scan gauge ii programmed for Cruze diesel. I would call them and have them answer your questions.


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## silvertank (May 26, 2015)

Thanks


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## IndyDiesel (May 24, 2015)

Welcome


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## cdb09007 (Aug 7, 2013)

Winter vs Summer Gas?


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## silvertank (May 26, 2015)

Should go up its diesle winter diesel causes a loss summer diese causes and increase


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## Kexlox (Nov 4, 2014)

silvertank said:


> Driving habits have been pretty much the same *other than ac* route is the same i used both or a blend depends whose cheaper usually a minor difference in the economy, no real traffic
> 
> 
> Sent from my iPhone using Tapatalk


Running the AC compressor drops my overall commute MPG from 46 to 42, or from 52 to 47 when I'm on the interstate. Note that the compressor comes on when you have it on floor only mode, regardless of what the AC button says.


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## silvertank (May 26, 2015)

Interesting, im still struggling to undersrand the guage now since it seems to wants to plummet for no reason. Maybe the ac does cause that much drag on the engine


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## IndyDiesel (May 24, 2015)

I recently added 35% ceramic tint all the way around, my ac still runs but not nearly as much and more important I am more comfortable faster on warm days. :grin:


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## silvertank (May 26, 2015)

Ive got the same tint makes a huge difference last summer i averaged 41 all summer with winter spikes around 43 so im still unsure why im loosinrg economy should have an oil analysis next week 


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## GlennGlenn (Nov 27, 2015)

Get a Scan Gauge II with the Cruze diesel firmware ( have to ask for it). The wealth of info it provides is invaluable. You won't regret the $150.00 you spend on it and it won't f*** with you car.


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## LulzT1 (Aug 24, 2015)

Type in CruzeDiesel and get $25 off when you order direct!


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## silvertank (May 26, 2015)

Ok thanks guys!!! 


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## silvertank (May 26, 2015)

Just an update had the oil changed no metal in it, gonna have it analysed, current hwy milage is around 31- 35 at 85 mph on my current trip seems like my mpgs keep dropping. 


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## Cruz15 (Mar 17, 2016)

Where are you located? You can Pm if u want.


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## silvertank (May 26, 2015)

Nashville Tn


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## Sperry (Aug 3, 2013)

check and make sure the under body panels haven't lost any clips and come loose . It would really effect the aerodynamics at 85 mph.. Try slowing down to 65 or 70 and see what your mileage is.. @ 65 you should get 50 mpg and @ 70 still be in the high 40's


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## Cruz15 (Mar 17, 2016)

silvertank said:


> Nashville Tn
> 
> 
> Sent from my iPhone using Tapatalk


If you were close I would see what I could do.
Just a guess but I had the Map sensor cleaned and the LTFT reset, fixed my mileage issues.
Cheers.


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## silvertank (May 26, 2015)

Cruz15 said:


> If you were close I would see what I could do.
> Just a guess but I had the Map sensor cleaned and the LTFT reset, fixed my mileage issues.
> Cheers.


Ltft?


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## Cruz15 (Mar 17, 2016)

Long term fuel trim.


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## silvertank (May 26, 2015)

Cruz15 said:


> Long term fuel trim.


Hmmm ill need to check that thanks


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## pandrad61 (Jul 8, 2015)

ummm 31-35 is not that far off at those speeds when in such hilly highways... when i went to lords town through Tennessee my mpg dropped since its very hilly. overall the whole trip i did 67.3 mpg but through Tennessee and Kentucky it was tough doing so even at 55mph. top off your tank, run factory tire pressure remove all non essential clutter in the car then try driving 100 miles on the highway at 55 mph cruise control and then top off again see what its at. my diesel compensated for altitude but i could feel a little under normal power compared to my home of Florida


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## silvertank (May 26, 2015)

pandrad61 said:


> ummm 31-35 is not that far off at those speeds when in such hilly highways... when i went to lords town through Tennessee my mpg dropped since its very hilly. overall the whole trip i did 67.3 mpg but through Tennessee and Kentucky it was tough doing so even at 55mph. top off your tank, run factory tire pressure remove all non essential clutter in the car then try driving 100 miles on the highway at 55 mph cruise control and then top off again see what its at. my diesel compensated for altitude but i could feel a little under normal power compared to my home of Florida


Depending on where i go usually i pull out 52 in the hills have since day one, but i have been averaging 42 on the same trip back and forth to work and on the trip to ms same route same speed every time then all of a sudden it dropped now im lucky to pull out 37. I keep track of every tank of fuel and lately it seems to be on the decline for no apparent reason.


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## pandrad61 (Jul 8, 2015)

ahh ok so its not so much a gradual decrease its a huge step off. hmm thats a strange one. do you think the computer may not be compensation properly for the high altitude? i could see it running a bit richer then it should thus burning more fuel and more frequent regens


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## ethana912 (Feb 24, 2016)

silvertank said:


> Just an update had the oil changed no metal in it, gonna have it analysed, current hwy milage is around 31- 35 at 85 mph on my current trip seems like my mpgs keep dropping.
> 
> 
> Sent from my iPhone using Tapatalk


Yeah I just took a long trip down I95 to Miami and set cruise on 80 the whole way and averaged 42 mpg.


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## obermd (Mar 3, 2012)

pandrad61 said:


> ahh ok so its not so much a gradual decrease its a huge step off. hmm thats a strange one. do you think the computer may not be compensation properly for the high altitude? i could see it running a bit richer then it should thus burning more fuel and more frequent regens


Anything under 3,500 ft (1,067 m) is considered low altitude. This has to do with a combination of overall air pressure and partial pressure of water vapor. The interesting thing is that turbo powered cars tend to do better as the altitude increases. This is because the turbo can maintain a consistent air pressure in the cylinders but the aerodynamic drag is reduced.

It's not altitude - something else is going on.


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## silvertank (May 26, 2015)

Right and no one at the dealer seems to not want to touch it unless i have something concrete to go on 


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## diesel (Jun 8, 2013)

I think the one question that was never asked is about the oil. You indicated that the oil was changed, then the MPG dropped. Improper oil can cause excessive regens which can cause poor fuel economy. Do you know 100% for sure what oil was used?


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## silvertank (May 26, 2015)

diesel said:


> I think the one question that was never asked is about the oil. You indicated that the oil was changed, then the MPG dropped. Improper oil can cause excessive regens which can cause poor fuel economy. Do you know 100% for sure what oil was used?


Yes i used liquimoly top tec 4605 and changed it, 


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## silvertank (May 26, 2015)

And its dexos2 approved i also just changed he oil again the other day went back to the total and its gotten slightly better economy not much 


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## GlennGlenn (Nov 27, 2015)

diesel said:


> I think the one question that was never asked is about the oil. You indicated that the oil was changed, then the MPG dropped. Improper oil can cause excessive regens which can cause poor fuel economy. Do you know 100% for sure what oil was used?



What if the oils original and never been changed ???


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## diesel (Jun 8, 2013)

silvertank said:


> And its dexos2 approved i also just changed he oil again the other day went back to the total and its gotten slightly better economy not much
> 
> 
> Sent from my iPhone using Tapatalk


OK, no issues there. What about fuel? Could biodiesel have been introduced into your fuel supply?


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## silvertank (May 26, 2015)

diesel said:


> OK, no issues there. What about fuel? Could biodiesel have been introduced into your fuel supply?


Ive used b20 on and off since ive had the car with not measurable effects in economy


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## Cruz15 (Mar 17, 2016)

B20 has more potential energy which should translate to better economy.

If anyone has a link that shows more soot being produced from Bio diesel I would like to read it.

Bio cleans everything incredibly well so if you dont use it from new you will get extreme cleaning action that could produce a little extra soot in the short term due to all the dirty deposits getting cleaned out of the fuel system.
My 2 cents.

I would rather run bio to be honest.


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## diesel (Jun 8, 2013)

According to this site, biodiesel makes for lower fuel economy

https://www.fueleconomy.gov/feg/biodiesel.shtml


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## silvertank (May 26, 2015)

To be honedt ive never noticed a difference


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## Cruz15 (Mar 17, 2016)

I was reading about green diesel sorry bout that, it has has a higher energy density and much higher cetane rating, which should give nice improvement to mileage.


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## pandrad61 (Jul 8, 2015)

ive not researched it much but i never run bio. here in Florida we have straight diesel. during lords town trip i had to use bio from pumps on highway. not a huge drop that i noticed but i did feel my cruze a bit weaker on throttle.


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## GlennGlenn (Nov 27, 2015)

pandrad61 said:


> ive not researched it much but i never run bio. here in Florida we have straight diesel. during lords town trip i had to use bio from pumps on highway. not a huge drop that i noticed but i did feel my cruze a bit weaker on throttle.


Anecdotally and from my "butt dyno", I'd have to agree that non-bio diesel is better from an acceleration standpoint than bio. Still getting frequent regens, but it's only been one tank on non-bio diesel. 

Only a real dyno could tell if non-bio is better...


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## 2014Oilburner (Feb 1, 2015)

Thanks for that answer...although I realized after I asked the question that I posted it in the wrong thread and deleted the question and asked it in another thread...but yea it seems so simple now....can't believe I couldn't figure it out.


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## silvertank (May 26, 2015)

Ok so ive narrowed out fuel as a factor, tire drop it by a bit but i was having the issue before they got swapped, no mods, waiting for my oil test to come back


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## diesel (Jun 8, 2013)

silvertank said:


> Ok so ive narrowed out fuel as a factor, tire drop it by a bit but i was having the issue before they got swapped, no mods, waiting for my oil test to come back
> 
> 
> Sent from my iPhone using Tapatalk


You just reminded me, tire pressure could be a meaningful factor.


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## boraz (Aug 29, 2013)

diesel said:


> You just reminded me, tire pressure could be a meaningful factor.


gator gets better mpg than 90% of us

on 36 psi


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## IndyDiesel (May 24, 2015)

boraz said:


> gator gets better mpg than 90% of us
> 
> on 36 psi


That does poke a hole in conventional wisdom. Plus his tires have 114k miles and still look decent.


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## obermd (Mar 3, 2012)

Tire pressure makes a difference, but not as much as you might think.


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## silvertank (May 26, 2015)

diesel said:


> You just reminded me, tire pressure could be a meaningful factor.


All tires stay around 37 to 38 psi like recommended


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## diesel (Jun 8, 2013)

silvertank said:


> All tires stay around 37 to 38 psi like recommended
> 
> 
> Sent from my iPhone using Tapatalk


I am running out of ideas to help you here. Did the dealer see if there are any pending codes?


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## silvertank (May 26, 2015)

diesel said:


> I am running out of ideas to help you here. Did the dealer see if there are any pending codes?


Nope they wont touch it unless i have something solid to go on because there are to many variables of what it could be. 


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## silvertank (May 26, 2015)

So oil came back completely normal and well within spec. So now im at a complete loss as to whats going on to cause this. Unless i have a leaking injector


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## diesel (Jun 8, 2013)

I have read on other automotive forums that the computer(s) can be reset by disconnecting the battery for X amount of time/ and possibly even touching the disconnected cables together. I am not sure if that holds true here so do so at your own peril. Maybe someone more familiar with that sort of thing can chime in. 

Here's a referenced article that seems legit, but again do so at your own peril!

How to Disconnect a Car Battery to Reset the Computer | eHow


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## obermd (Mar 3, 2012)

Resetting the computer by pulling the plug works on the gas models. I don't see a reason why it wouldn't on the diesel models as well.


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## silvertank (May 26, 2015)

So after much more driving and a new dealer they think they have a handle on it. Turbo blew a seal and just came apart today so they are replacing it and think it was the cause of the loss in fuel economy


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## diesel (Jun 8, 2013)

silvertank said:


> So after much more driving and a new dealer they think they have a handle on it. Turbo blew a seal and just came apart today so they are replacing it and think it was the cause of the loss in fuel economy
> 
> 
> Sent from my iPhone using Tapatalk


Wow, that's scary because a blown turbo seal can cause a runaway diesel in some cases. This is the first I've heard of any turbo issues on our cars. Can you go into more detail about what exactly happened to your turbo?


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## silvertank (May 26, 2015)

They arent sure its been in the shop for 4 days all they elaborated to was a seal blew and was causing the boost to leak and cause the loss in power and fuel economy. Ill try go find out more once i get it back 


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## diesel (Jun 8, 2013)

silvertank said:


> They arent sure its been in the shop for 4 days all they elaborated to was a seal blew and was causing the boost to leak and cause the loss in power and fuel economy. Ill try go find out more once i get it back
> 
> 
> Sent from my iPhone using Tapatalk


Thanks for the update. Keep us posted. That sounds like something different than a seal inside the turbo.


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## 1877 iris ave (Sep 23, 2011)

Post #60 by OP If I understand it correctly you changed tires, are the new ones Low Rolling Resistance tires?


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## diesel (Jun 8, 2013)

1877 iris ave said:


> Post #60 by OP If I understand it correctly you changed tires, are the new ones Low Rolling Resistance tires?


Great point!


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## silvertank (May 26, 2015)

Yes new tires are lrr. turbo was replace was leaking between the case halves sealed the system back up, advised its been leaking for a while and was probably the cause of the loss in economy


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## diesel (Jun 8, 2013)

silvertank said:


> Yes new tires are lrr. turbo was replace was leaking between the case halves sealed the system back up, advised its been leaking for a while and was probably the cause of the loss in economy
> 
> 
> Sent from my iPhone using Tapatalk


Very interesting. i assume that was covered under powertrain warranty? have you noticed a difference in fuel economy since the replacement?


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## silvertank (May 26, 2015)

Covered under warranty fuel economy seems to have come back but i havent put much on it since power is back now. Ill post back after next week im doing a 1300 mile round trip next week


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## diesel (Jun 8, 2013)

silvertank said:


> Covered under warranty fuel economy seems to have come back but i havent put much on it since power is back now. Ill post back after next week im doing a 1300 mile round trip next week
> 
> 
> Sent from my iPhone using Tapatalk


i am glad to hear it was covered. Keep us posted on the results!


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## silvertank (May 26, 2015)

Fuel economy came back less than a week later









Emissions failure crippled the car, just dropped it off ill see what happened


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## silvertank (May 26, 2015)

Dealer found out its a pcv valve heater failure, not under warranty down for a week till it comes in 


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## diesel (Jun 8, 2013)

silvertank said:


> Dealer found out its a pcv valve heater failure, not under warranty down for a week till it comes in
> 
> 
> Sent from my iPhone using Tapatalk


Ouch! Tell your car "that's enough!" Hopefully there's a light at the end of this tunnel


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## silvertank (May 26, 2015)

Hahaha right upside im getting the upgraded audio system from chevy at half cost so thatll work 


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