Winter Diesel Cetane and Decreased Seasonal MPG

A write up from my friend PrivatePilot at DP Ontario Chapter
Winter Diesel, Cetane, and decreased MPG.
In the last few weeks it seems that that there has been a lot of threads dealing with decreased fuel economy with the arrival of colder winter temperatures.

Although many of us know why, many new diesel owners, or those perhaps dealing with the joys of winter diesel or cold temperatures for the first time may not know exactly why their MPG has suddenly taken a nose-dive.

So, I thought I'd write a little FAQ. At least this way I can link to it from my signature and point people towards this (hopefully useful) information instead of typing it out over and over again.

- What's "Winter Diesel"?

First, it's important to know that diesel fuel normally has a very high paraffin wax content. In the summer this is really of no concern as your fuel is never cold enough for this wax to create problems, but in the winter, this wax content can lead to fuel clouding/gelling, a situation that can lead to a clogged fuel system and the inability to start your engine.

Winter diesel is effectively regular diesel fuel but with additives (and some suggest, a slightly different refining process) that help reduce clouding and gelling of the fuel making for a more carefree winter season once the weather gets cold.

- Why does it reduce my MPG?

It's well known that these additives and changes in the formulation of winter diesel reduces the fuels level of Cetane.

What's is "Cetane"? While gasoline's octane number signifies its ability to resist auto ignition (AKA detonation), diesel's cetane number is a measure of the fuel's delay of ignition time (the amount of time between the injection of fuel into the combustion chamber and the actual start of combustion of the fuel charge).

Because a diesel engine has no ignition system, the fuel itself must be able to ignite under pressure. The sooner the better.

A reduced Cetane rating reduces the ability of the fuel to auto-ignite, a process that eventually leads to lower fuel economy, sometimes only a slight change, but in the case of many of us here with larger pickups, sometime a drastic drop.

-What's the season for Winter Diesel?

Winter blend diesel is common in most northern US States and all Canadian provinces from about late October until late April or May. Depending on how large the tanks are at your choice of fueling location, and the volume of fuel they sell, sometimes winter diesel may linger in the stations tanks later into the spring until fresh "summer" diesel is delivered.

- What can I do to recover this lost cetane?

There are several options that can help your fuel mileage when dealing with winter and a diesel engine. Dealing directly with the lower cetane rating of winter diesel, you can use a cetane booster. A quality product such as Stanadyne Performance Formula not only significantly boosts the cetane level, but also provides added lubricity for the diesel engines fuel and injection pump systems.

There are many other cetane boosters out there, but many do not post any statistical information on how much they actually boost the cetane rating of the fuel, so your mileage may vary.

Although the per-tank costs may seem high for a quality additive like Stanadyne, when you sit down and crunch the numbers it can quickly more then pay for itself on a tank-by-tank basis. If you're going to spend $2/Tank on a lubricity additive anyways, why not spend the $3/$4 per tank for some quality additive during the winter months that will actually significantly raise your cetane while providing injection pump lubricity at the same time?

- What else can I do to get my MPG back up?!

There are lots of other options, although arguably none will have as much as an effect as dealing with the cetane rating of your fuel first.

1/ Plug in your truck. A few hours of block heater time before your morning commute will help your engine start easier and can lead to notably reduced fuel use while your engine heats up. If you use a timer to run the heater for only 2-3 hours (all that is needed) the electricity cost can be very little.

2/ Change to synthetic fluids. 0W40 or 5W40 diesel engine oil flows easier in the cold, and not making your engine pump molasses-like 15W40 will aid in fuel economy. If money is no object, converting to fully synthetic oils in your transmission, differential(s), and transfer case (if equipped) can also have a notable effect. Just be sure to switch back to regular 15W40 diesel oil come the spring!

3/ Check your tire pressures! Yep, many of us have forgotten about those tires, but low tires alone can mean +15% more fuel use! Yes, nobody likes crawling around in the howling wind or snow and checking your tires (especially for those of us with duallies) but you may find yourself shocked at how low your tires have gotten since you last checked them in the hot summer months.

4/ Drive conservatively. This really goes for all year round, but in the winter especially your engine works that much harder to make your truck move, and pushing that pedal harder and harder only ends up using more and more fuel.

5/ Don't idle! A surefire way to kill your MPG is to idle. An idling truck gets ZERO MPG. Contrary to old-school tales of years passed, you don't need to idle a modern diesel constantly for fear or it never re-starting in the cold, nor is idling your diesel for 20 or 30 minutes before driving away after a cold start necessary. The contrary, on some diesel engines, idling can actually be harmful - On the newer diesels, all idling serves to do is clog your DPF system, and on old diesels it can cause issues like wet-stacking. It's a waste of fuel and potentially harmful to your engine, so if you really care about $$$, simply don't idle. Start your engine, wait for your oil pressure to build and stabilize, and drive gently away. Wait a minute or three if it makes you feel better, but any more than that is really a waste. Take it easy for the first mile or three, and then drive normally.

It's important to note that your winter MPG, even taking everything above into consideration, will likely never equal your summer MPG. Small things like increased rolling resistance of cold tires, the fact that fluids never reach the same temperatures as they would in summer, amongst other things *always* take a permanent toll on your fuel economy in the winter, but with some knowledge (and some Cetane!) you can put up a valiant fight none the less!

Comments or additional suggestions welcome.

I have yet to put a fuel additive in my tank this winter, I've never had a problem with waxing/gelling because of winter fuel, I idle my truck for a good 10-15 mins because otherwise its like a freezer inside lol, Mileage isnt really a concern because if it was I would be like Robert and buy a TDI Jetta

Well I had to give it a try. On the advice of my friends at DP I went out and found a bottle of POWER SERVICE ( a winter diesel conditioner )

All I have to say is WOW !!! I could immediately notice the difference in the throttle. Now I'm beginning to notice it in my DIC

As soon as I get throw this tank.. I'll let you know the numbers . I can tell, I was burning an avg. of 27L per 100 before the Power Service additive.

Keep in mind, most D1 is not straight diesel, D2 is. D1, which is used mostly in the winter, is 15-50% Kerosene. Since Kerosene is a much lower BTU content, that alone will create lower fuel economy. On top of that, the cold (oil, grease, etc..) creates more resistence so it takes more energy to move the vehicle.

And Glenn, make sure any fuel additives you buy are rated for use with a DPF equipped vehicle.

I've never noticed a change in mileage/performance with any additive that I've used, I've tried PS white bottle and cant say it did much for me... ive tried howes... kleen flow... even 2 cycle oil, none of it really made a big difference, for me just buying good fuel makes a difference, going from the crappy local stuff to fuel from like a Flying J... thats makes a difference in mileage at least

merlin5577 wrote:

And Glenn, make sure any fuel additives you buy are rated for use with a DPF equipped vehicle.

I got this Power Service winter additive cetain boost on a tip from one of the local diesel guys here, and he is also a member of DP.
I've been hanging out with this group since last summer. Great bunch of guys, very knowledgeable and a lot of fun when we all go to the track.
So any suggestions and tips I can get from them is usually tried tested and true with one or two of the members.
But I will reread the bottle and go to the website to insure it is definitely safe for my truck.

In2Trux wrote:

merlin5577 wrote:

And Glenn, make sure any fuel additives you buy are rated for use with a DPF equipped vehicle.

I got this Power Service winter additive cetain boost on a tip from one of the local diesel guys here, and he is also a member of DP.
I've been hanging out with this group since last summer. Great bunch of guys, very knowledgeable and a lot of fun when we all go to the track.
So any suggestions and tips I can get from them is usually tried tested and true with one or two of the members.
But I will reread the bottle and go to the website to insure it is definitely safe for my truck.

PS is not one of the best additives, it ranks #10 in the test below, it actually ranks worse than 2-cycle oil

OPTI-LUBE XPD is practically the best for lubricity, one step down from bio-diesel, If you're really into putting an additive into your tank I would seriously look into it http://www.opti-lube.com/XPD.htm

Also Check out this thread on DP, Its a pretty comprehensive test, keep in mind that the fuel in this test was pure #2, no additives were added at the refinery, so it is worst case scenario, and the fuel your getting at the pump has additives to replace the lost lubricity, so the additives wont have the same effect on the fuel you get at the pump, and the lower ones may actually make pump fuel WORSE! http://www.dieselplace.com/forum/showthread.php?t=177728

This test is the reason that I personally see no need to add anything to my tank, if i could get Opti-Lube easily without having a petroleum product shipped up north from the internet I would consider using that, anything else doesn't seem worth it

Thanks Ram I'll check those out

Also keep in mind guys, the LMM was designed with ULSD in mind so adding lube to the fuel wont do as much as it would with an LBZ or older.

merlin5577 wrote:

Also keep in mind guys, the LMM was designed with ULSD in mind so adding lube to the fuel wont do as much as it would with an LBZ or older.

FWIW the LMM and LBZ share the exact same fuel system, except for the injectors, they changed the tips from 7 hole in the LBZ to 6 hole in the LMM, the cp3, rails, everything is the same, the ECM is the same etc., and I agree, additives aren't going to do as much on these engines as they would on say a 6.2/6.5 or a 5.9 12v, but the newer common rail engines are much pickier about the fuel they run, a GOOD additive will help, but like i stated, the winter fuel you buy at the pump is already treated with additives to increase lubricity and anti-waxing

Im not at all opposed to hearing about what kind of real gains you guys are getting with these additives, Keep us all informed

i added a can of cetane to my blazer and it blew my motor.. WFT.. i thought you knew what you were talkin about glen..

007jimmy wrote:

i added a can of cetane to my blazer and it blew my motor.. WFT.. i thought you knew what you were talkin about glen..

I hope you're kidding.

no why would you think i was kidding.. the fuel was gelling up and i was having a hard time starting it.. i added a gallon of cetane and it started up for all of .5 of a second and then there was metal frying EVERYWHERE...

007jimmy wrote:

no why would you think i was kidding.. the fuel was gelling up and i was having a hard time starting it.. i added a gallon of cetane and it started up for all of .5 of a second and then there was metal frying EVERYWHERE...

You got to be kidding. I don't believe you LOL I know, you know better LOL

lmao... yeah figured i would have a little fun with it since you guys are always bustin on my and my gassers.. lol