# Sudden Increase in MPGs



## Rivergoer (Mar 30, 2017)

Might have something to do with regen frequency. Regens consume fuel, negatively impacting mpg.

I’ve noticed averaging 60 mph regens occur about 650-700 miles. If I avg 70 mph regens happen around 850 miles.


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## VtTD (Nov 5, 2013)

Yeah, but this is between regens where I'm noticing the higher MPGs. IE I wouldn't get this kind of mileage between regens before something apparently changed.

btw, sorry for posting in the tech discussion board. Meant to go into general discussion.


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## Taxman (Aug 10, 2017)

The Italian Tune-Up has long been associated with diesel cars, perhaps it works with modern common rail engines too?

Perhaps some other light throttle users could try blasting up a high speed hill or two at full throttle and report the results.
With a 30 year old Mercedes, you get a nice black cloud when you do that, and then reduced smoke for a month or so.


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## TX CTD (Oct 24, 2014)

My wife's CTD seems to be getting better mileage and it's been deleted for about 5 months now. I don't calculate it by hand unless we are on a long trip, I just observe what 50 mile avg is and what I can get it up to where ever we are going. Some of those same trips happen often so I have a pretty good idea about where I expect it to be when I'm done. Overall I would say it been about 5 mpg above where I expect. 

While I'm pleased, I think the time of the year has a lot to do with it. The winds tend to die down here in the fall and the cooler air make a little more power. I think those 2 things probably account for most of the gain. 

Something I'm kind of surprised nobody here has done is have a look in the intake. That seems to be a common thing with the TDI crowd and also with the BMW diesel folks as well. Over time the EGR starts to clog up the intake and a good cleaning restores the power and mileage. I haven't heard that mentioned with the CTD and I haven't heard anyone complain much about loosing mileage and power over time.


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## Rivergoer (Mar 30, 2017)

TX CTD said:


> While I'm pleased, I think the time of the year has a lot to do with it. The winds tend to die down here in the fall and the cooler air make a little more power. I think those 2 things probably account for most of the gain.
> 
> Something I'm kind of surprised nobody here has done is have a look in the intake. That seems to be a common thing with the TDI crowd and also with the BMW diesel folks as well. Over time the EGR starts to clog up the intake and a good cleaning restores the power and mileage. I haven't heard that mentioned with the CTD and I haven't heard anyone complain much about loosing mileage and power over time.


100% yes...Wind and air temp are BIG factors. Calmer cooler climate can easily bump CTD 5 mpg.

EGR...what a coincidence, I just pulled mine today to have a look-see. ‘14 CTD 76,000 miles. Followed the thread by @MP81 with great input from @boraz and @IndyDiesel. 

http://www.cruzetalk.com/forum/64-g.../210810-my-egr-throttle-plate-experience.html

No CEL, no rough running or mechanical issues...just curious. While the EGR was soot-covered, it wasn’t alarmingly so. I used a good carb/intake manifold cleaner with an old toothbrush and got it looking new again. 

Just completed a 250 mile drive from AZ to California. Mileage was good as expected for that drive, no earth-shattering changes. Nonetheless, glad I did this. Took about 45 minutes with a T-Handle T30 torx and a 10mm socket. Here are some before and after shots


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## TX CTD (Oct 24, 2014)

I'm sure mine is just about that nasty, the delete was done about 70000 miles. It's just weird that it doesn't seem to phase the Cruze, but it has a noticeable effect on other diesels with the same miles. I've been kicking around the idea of a BMW 335d and general consensus seems to be clean it out every 40000 miles. I believe Diesel's car was running almost the same as new with no cleaning @ 200000 miles.


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## MP81 (Jul 20, 2015)

Rivergoer said:


> 100% yes...Wind and air temp are BIG factors. Calmer cooler climate can easily bump CTD 5 mpg.
> 
> EGR...what a coincidence, I just pulled mine today to have a look-see. ‘14 CTD 76,000 miles. Followed the thread by @*MP81* with great input from @*boraz* and @*IndyDiesel*.
> 
> ...


Good work! Looks pretty similar to how mine looked as well. I can't say I've seen any improvements in mileage, but like you said - the peace of mind is well worth it.


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## Lugnut (May 4, 2017)

Another reason, depending on where you live, is because the fuel suppliers are starting to change the fuel blend over for the cooler weather. This does not apply to everyone, but to the majority of us, this is a benefit of cooler weather.


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## VtTD (Nov 5, 2013)

Lugnut said:


> Another reason, depending on where you live, is because the fuel suppliers are starting to change the fuel blend over for the cooler weather. This does not apply to everyone, but to the majority of us, this is a benefit of cooler weather.


I thought with diesel winter blend = lower MPGs. 

Had a 600 mile or so weekend. Probably all but 5-10% of those miles on the interstate with cruise at at 70 most of the time. 60-65 at the slower areas. Somehow managed 66.8mpg over 25 miles, 62.1 over 50 and 51.2 over 500. Really incredible compared to what I have gotten in the past. I think a year or so after I got the car I got to like 63 over 25 miles once but that was on a 50mph road with almost no stops/slow downs. Never hit 60 again that I knew of. Was constantly crossing 60 for short times this weekend.


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## Lugnut (May 4, 2017)

VtTD said:


> I thought with diesel winter blend = lower MPGs.
> 
> Had a 600 mile or so weekend. Probably all but 5-10% of those miles on the interstate with cruise at at 70 most of the time. 60-65 at the slower areas. Somehow managed 66.8mpg over 25 miles, 62.1 over 50 and 51.2 over 500. Really incredible compared to what I have gotten in the past. I think a year or so after I got the car I got to like 63 over 25 miles once but that was on a 50mph road with almost no stops/slow downs. Never hit 60 again that I knew of. Was constantly crossing 60 for short times this weekend.


It all has to do with the cetane rating of the fuel and the additive packages the fuel suppliers are adding. Have you noticed that diesel fuel prices jumped up when hurricane Harvey hit the gulf, just like gasoline prices? Have you also noticed that gasoline prices have dropped back down and are dropping more rapidly than diesel fuel prices? This is because the blends of the diesel fuels are changing in some markets. This is particularly true in the northern US and Canada. 

Let me try to give you a lesson on cetane. Cetane identifies the fuels ability to ignite. The higher the cetane number, the easier the fuel will ignite. For high-speed common-rail diesels such as the CTD, higher cetane = better fuel economy. This is one reason why cetane boosters are so popular with diesel enthusiasts. High cetane will also benefit low-speed diesel engines, but only to a point. If the fuel ignites too quickly on a low-speed diesel the engine will loose power and make a lot of noise. So fuel suppliers have to find the balance between high-speed diesel engines and low-speed diesel engines. A cetane rating of around 40-45 will usually do the trick in the summer months. 

During the cooler months of the year, diesel fuel must ignite more easily. To achieve this, diesel fuel suppliers increase the cetane and place additives in the fuel to prevent it from gelling or even solidifying. These additives work well in cold climates but not as well in warm climates. A good example is a vehicle that fills up with fuel in Florida in January. The vehicle will run great, have good fuel economy, etc. That vehicle has several fuel tanks that were all filled at the same time and give the vehicle a tremendous driving range. That vehicle drives from south Florida to northern Vermont. When the vehicle left Florida is was 80 degrees. Now the vehicle is in Vermont, the air temperature in 10 degrees above zero. The owners tries to start the vehicle and it fails to start. This is because the fuel is not conditioned for the colder weather. Take the vehicle inside, warm it up, and the engine starts right up. (By the way, this is a real story). The cause of the concern is summer fuel being used in a winter environment. So what is the difference? The cetane and the additives. By increasing the cetane, the fuel will ignite easier and thus start better in cold weather. 

So the question becomes why does a diesel engine fuel economy drop in the winter? Diesel engines need heat to efficiently ignite the fuel. In the winter months, diesel engines struggle to warm up. So to help with this, diesel fuel suppliers increase the cetane which causes the fuel to burn easier. Winter fuel ignites easier, but it also looses BTUs (energy). So it takes more fuel to do the same work compared to when it is warmer. Consume more fuel, fuel economy drops. 

So why did Lugnut say that depending on where you live, your fuel economy increase could be caused by the fuel suppliers changing over the fuel to the winter blends? Well folks in the northern US and Canada will likely see the biggest increase in fuel economy right now because the temperatures outside have been relatively mild. As the temperatures continue to slide down, the fuel economy will likely drop as well. Fuel suppliers in the northern most states begin changing over their diesel fuel blends around September and other areas begin following suit in late September and early October. This process is a gradual process and is done on purpose. If a fuel supplier were to change over their fuel to a full winter blend, this would cause the vehicles that use the fuel to go into shock unless the ambient temps supported the drastic change. Low power, poor fuel economy, increased noise would be some of the symptoms. Consumers would loose faith in the fuel company and eventually their sales would suffer. So right now with warmer weather and higher cetane rates fuels, we are benefiting from better fuel economy. 

I know this is a lot to read, and I doubt many will read the whole story. It is a complex situation and it is not applicable to everyone. However, if you are experiencing a sudden change in fuel economy for no good reason and you also happen to live in a more northern area, the fuel change over could be the cause. If your diesel fuel prices have not dropped, it is likely the fuel is being changes over and resulting in the higher prices. 

I hope this helps explain this a little better.


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## MRO1791 (Sep 2, 2016)

I cleaned the Oxygen sensor on one of my cars, with 54k and did see a increase in MPG. The sensor can get soot covered and read inaccurate, which affects MPG, but many factors affect MPG. 

Sent from my Moto G (4) using Tapatalk


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## boraz (Aug 29, 2013)

Lugnut said:


> It all has to do with the cetane rating of the fuel and the additive packages the fuel suppliers are adding. Have you noticed that diesel fuel prices jumped up when hurricane Harvey hit the gulf, just like gasoline prices? Have you also noticed that gasoline prices have dropped back down and are dropping more rapidly than diesel fuel prices? This is because the blends of the diesel fuels are changing in some markets. This is particularly true in the northern US and Canada.
> 
> Let me try to give you a lesson on cetane. Cetane identifies the fuels ability to ignite. The higher the cetane number, the easier the fuel will ignite. For high-speed common-rail diesels such as the CTD, higher cetane = better fuel economy. This is one reason why cetane boosters are so popular with diesel enthusiasts. High cetane will also benefit low-speed diesel engines, but only to a point. If the fuel ignites too quickly on a low-speed diesel the engine will loose power and make a lot of noise. So fuel suppliers have to find the balance between high-speed diesel engines and low-speed diesel engines. A cetane rating of around 40-45 will usually do the trick in the summer months.
> 
> ...


check my fuelly, my mpgs do not change, 100f summer, -40 winter, same mpg.

studded tires, summer tires, same mpg


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## IndyDiesel (May 24, 2015)

I see about 1-2 mpg decrease in mpg and I use fuelly as well. I don’t pay too much attention, the biggest decrease I see is due to wind and just colder temps. If it’s windy, it’s much more than 1-2 decrease.


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## Cruzator (Dec 31, 2014)

I see a slight drop in winter mileage well. I attribute it to the increased warm up time before I start driving the vehicle. I typically like the coolant temp at least 100F before I start driving in the winter. This is the same temp the car comes off of "fast" idle. I'm not sure why the OP had a sudden increase in mileage (especially if it's over multiple tanks), but I wouldn't complain. As mentioned before, there are many factors that can affect this, so we can control, and many we can't.


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