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Diesel Discussion........


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I was reading in a non-RV forum when this post appeared about diesel trucks. It has lots of interesting observations and comments. I have NO background to judge the quality or veracity of the information. So I am posting a copy here and hoping you diesel experts chime in on his comments. I was particularly interested in the lubricity issue, water and others that directly relate to RV' travel. Thanks.


Diesel fuel is wunderbar. It costs much less to refine than gasoline. It produces more energy per gallon than gasoline. In Europe, where people are smart and energy prices are high, diesel vehicles outsell gasoline vehicles. But buying a modern clean diesel in the United States isn't as simple as putting fuel in it and changing the oil on time. Why?

As wonderful as diesel is, older formulations produced massive amounts of particulate emissions, a contributor to acid rain and other environmental threats. To clean up diesel fuel, legislators (in Europe mostly) started regulating the permissible sulfur content levels of diesel fuel. By reducing the sulfur in diesel, the particulate emissions from burning it decrease. But removing sulfur from diesel also reduces the fuel's lubricating properties.

Adequate lubrication is essential for the proper functioning of high pressure diesel fuel delivery systems. By removing the sulfur and therefore some of the lubrication from the fuel, components like the fuel pump and injectors suffer increase wear. Failure of fuel delivery components can be catastrophic as it can send shrapnel from the fuel pump throughout the engine. Worst case, that is a massively expensive repair.

But wait, there's more. Lack of lubricity isn't the only potential issue affecting diesel fuel and engine reliability, performance and durability. Contamination of the fuel (typically with water or gasoline from the gas station's fuel tanks) is another potential problem. Lastly, the energy content of diesel fuel is rated using "Cetane" rather than "Octane". Manufacturers of diesel vehicles also provide minimum recommended Cetane values for their motors. Optimal combustion and emissions system function and longevity is affected by the Cetane rating of the fuels used.

So how do you, the would-be owner, navigate these issues (sufficient Cetane, proper lubricity, freedom from contamination) to enjoy the benefits of diesel power - clean, efficient and high-torque fun?

Cetane Deficiency:

Let's start with Cetane as it's the easiest to cover. BMW, for example, recommends ULSD (Ultra Low Sulfur Diesel) fuel with a minimum Cetane rating of 50 for its diesel vehicles sold in North America. Other manufacturers require from the mid-40s to 50 or better. So what's the problem? US law permits sale of ULSD with Cetane ratings as low as 40, which is well below the recommended levels set by vehicle manufacturers. Here are the claimed Cetane ratings for several US refiners:

BP (Amoco branded), 51;
Countrymark fuels Diesel-R, 50
Chevron, 49; or 51 with Techron D labels in select markets
ConocoPhillips through the 76 stations (California) 47-53
PetroCanada, 47-51
BP (Powerblend 47, otherwise 40-42)
Shell, 46;
Sinclair, 46;
Sunoco Gold, 45 (often +1-5) Sunoco regular is usually 40.
Exxon/Mobile, 43-46
Holiday Stations, 40-43
HESS, 40-42, can be up to 45.
Husky, 40 + diesel Max additives raise another 1-3 from there (41-45 max)

Pilot/Love's/Flying J/Valero/Sheetz/Walmart/Wawa: 40

Not very pretty is it? Most US ULSD (Good old Diesel #2) doesn't meet the Cetane requirements for consumer diesel vehicles. So what can you do about low Cetane fuel and what happens if you don't do anything at all about it? You can add additives to the fuel. In the case an additive that boosts Cetane. Or if you do nothing and habitually use fuel rated below the minimum optimal rating you can expect sluggish performance, rough idle, increased emissions, a shorter lifespan for your emission system components, and reduced fuel efficiency. It won't "break" your car quickly but it will impact its performance and efficiency and potentially compromise longevity of certain systems. If your vehicle uses Urea injection, it will also increase your Urea additive (AdBlue) consumption and AdBlue isn't inexpensive. In the grand scheme of things though, low Cetane isn't a major risk; it's a minor inconvenience.

Insufficient Lubricity:

ULSD fuel lubricity is measured by measuring the scarring caused by impurities in the fuel on metallic fuel system components. The lower the lubricity, the larger the dimensions of the scars. The unit of measure used to measure such scarring is the micron. The scarring potential of fuel is tested using a device called a High Frequency Reciprocating Rig (or "HFRR"). Fresh ULSD contains no additives of any kind, though it may contain contaminates and may vary in lubricity by virtue of variances in the refining process. No station pumps raw diesel. Raw ULSD fuel can range from 900 microns to 600 microns in HFRR rating. When a refinery sells ULSD, the distributor or retailer is required to add lubricity additives sufficient to meet legally specified minimum lubricity standards. In the United States ULSD fuel (Diesel #2) legally must have an HFRR lubricity rating of 520 microns or less. But it frequently it does not meet this standard.

In one test the tester sampled retail diesel fuel from stations in 13 different states. Only 7 retailers met the legal 520 micron or better standard. 6 of the retailers provided fuel ranging from 605 microns to 845 microns(!) in HFRR rating. Yep, it looks like about half the distributors/stations in the country minimally treat or do not treat at all the raw diesel fuel the sell. There's a special place in Diesel Hell for such scumbags, but I digress.

So why does the HFRR rating of the fuel matter? Because almost every consumer clean diesel vehicle sold in the United States uses a high pressure fuel pump (HPFP) manufactured by Bosch. Bosch's maximum HFRR rating for its HPFP? 460 microns or less. Houston we have a problem. Though US law permits the peddling of fuel with an HFRR rating of up to 520 microns, and about half the time US retail ULSD fuel fails to meet even this lax standard, the fuel systems in the vehicles into which this gritty fuel is going risk accelerated wear and premature, catastrophic failure of the fuel delivery system including the HPFP and injectors. Easily a $8k to $10k repair bill potential. There's a 60 micron gap between what's legally allowed in the US and what is permitted by the HPFP manufacturer.

Why do vehicle manufacturers sell vehicles in the US that have a HPFP that requires greater lubricity than our fuel provides? Europe. It's always Europe's fault. Europeans buy a lot more diesel consumer vehicles than Americans. In Europe their fuel quality regulations are much, much tighter, the enforcement much more aggressive and the penalties for violation much more severe (you get caught pushing raw diesel in Germany and you'll *wish* they sent you to Diesel Hell). As a result Europeans enjoy ULSD fuel with superior lubricity (460 - hey! Just like the Bosch pump!) and Cetane (51 minimum) ratings compared to us, their poorer and more (diesel) ignorant cousins across the pond.

So owning a modern clean diesel in the US means that you need to worry about Cetane ratings (a little) and lubricity (a whole lot). What do you do about these risks? Additives. Like the additives that the US retailers or their distributors are legally supposed to be adding to raw ULSD fuel). There are many different kinds of diesel fuel additives available to consumers. You'll want one that increases lubricity. You may also benefit from one that increases Cetane. But there's a catch. There are no additives that address *only* lubricity or *only* Cetane or *only* these two, which brings us to the issue of contaminated fuel.

Diesel Fuel Contamination:

It's clean when it leaves the refinery. It gets contaminated, if at all, when it sits in storage either at a distributor's storage facility or in gas station pumping tanks. The two most common varieties of contamination are gasoline and water contamination. Gasoline contamination occurs when the storer puts diesel in a container that formerly stored gasoline and fails to remove all of the gasoline from that container first (aka "churlish laziness and sloppiness"). Gasoline in diesel fuel radically reduces its lubricity. Filling your near empty tank with gasoline accidentally and then driving away can almost instantly destroy your HPFP - boom. Blending 10k gallons of treated ULSD with 400 gallons of gasoline, makes for dirty poor lubricity fuel, but probably not catastrophic fuel pump failure. The cure for distributor and dealer gasoline contamination is using a lubricity additive when you fuel up. The cure for accidentally filling your own tank with gasoline instead of diesel is having the vehicle towed to a service center to have its stomach pumped.

Water contamination occurs due to leaky storage tanks. Water, like gasoline, reduces fuel lubricity. Water also can corrode the fuel delivery system. Water also allows biological contamination of diesel fuel. That's right. Water is heavier than diesel and will collect at the bottom of the tank (storage or your car's fuel tank). Amoeba and other foul and fetid micro-organisms will go forth and multiply in the water in your tank and eventually as the amount of water increases sacrifice themselves to gum up the works. Disgusting. So water in diesel fuel is triply bad. How do you deal with water in your diesel?

1. Pray. Pray that your distributor and retailer aren't complete idiots with water filled tanks.

2. Some vehicles have fuel filters that include a water separator. Theoretically heavier water is trapped and dropped into a separate container when fuel passes through the filter. You periodically empty the captured water from this container. Most cars however do not have water separators. It's more of a truck thing.

3. Additives do different things with water. You have emulsifiers, demuslifiers, encapsulators and biocides. Biocides kill critters in the water in your tank, so they don't eliminate water but rather one of the downsides of having water in your fuel. demuslifiers, emulsifiers, encapsulators and such, work on the water. Allegedly demuslifiers cause the water to clump into more massive gloubules and fall out of suspension in your fuel...where though? Most suspect in the fuel filter. But if you don't have a water separator this means that demulsified water should build up in your filter housing reducing the filter's fuel filtering effectiveness. Emulsifiers theoretically suspend the water in very tiny droplets in the fuel in such a manner that they don't affect lubricity and burn off as steam during combustion. The thing is, your diesel motor isn't supposed to burn water and critics say that emulsified diesel causes fuel delivery system corrosion and wear. Encapsulators are kind of a made up marketing term. The marketing-speak is that they are a better kind of emuslifier. Who knows.

In any case, water in the fuel - anywhere - emulsified, demulsified or otherwise is bad.

Curve Ball:

Many diesel fuel sellers shirk their responsibility to add additives to the fuel necessary to meet weak US lubricity requirements. Many of them, however, do use sufficient additive. What you'll never know is, beyond lubricity, what other characteristics do the additive used at the retail level have in them. Some have emulsifiers, some have demulsifiers, some have Cetane boosters, some have biocides, some have fairy dust. It's important to keep that in mind when deciding whether to add an additive when you fill up and if so what kind of additive you should add.

What Do I Do and Why?

The #1 threat to these powertrains in the US is our *krappy* lubricity diesel fuel. You are almost 100% guaranteed that no matter what the fuel you buy in the US it will NOT meet your HPFP maker's requirements. I use a lubricity additive. There are a couple I like. and we'll talk about why in a second. My vehicle has a simple fuel filter without a water separator. I can't buy any lubricity additive that doesn't also do something with respect to water in the fuel (they all have an emulsifier or demulsifier of some sort). Biodiesel (made from corn) has great lubricity. If I could get it I would run B2 (ULSD with 2% biodiesel) or B5 (ULSD with 5% biodiesel). But where I live we don't get biodesel at all. So I'm left with lubricity additives.

In 2007 there was a test done by diesel engineer Arlen Spicer that tested the HFRR lubricity rating improvement of many different additives when added to raw ULSD (636 micron HFRR rating). The report was full of surprises. Some additives actually reduced lubricity. Some did virtually nothing to improve lubricty despite being advertised as improving lubricity. Some commendably boosted lubricity. You can read that report here:


The two I like and have used are Stanadyne Lubricity (not to be confused with the nearly useless from a lubricity perspective Stanadyne Performance) and Opti-Lube XPD. Stanadyne Lubricity is good for a 157 micron lubricity improvement when added to untreated raw diesel. Opti-Lube XPD is good for a 319 micron improvement.

When I can get Chevron or Chevron D ULSD I use Stanadyne Lubricity as that fuel has sufficient Cetane and Stanadyne adds only lubricity and a water demulsifier (more on this in a bit - it's a potential problem). My theory is that if I'm otherwise in spec on my fuel or close to it, there's no benefit to boosting Cetane and I don't know whether there's a downside to the other characteristics of a broadband additive.

When I travel and find myself potentially stuck with low Cetane and very poor lubricity fuels often served up by interstate truckstops like Pilot, I run Opti-Lube XPD. Optilube boosts Cetane, boosts lubricity, contains a demulsifier, and also has chemicals to prevent gelling in cold climates and a host of other wonders. It's "multi-purpose". It's also a little cheaper than Stanadyne. But I really only want to treat the problem I know that I likely have (low lubricity) which is also the biggest potential problem facing these motors, and not recreationally medicate for lesser severity problems I might or might nit have, so broadband Opti-Lube XPD (which is a better lubricity booster than Stanadyne Lubricity) is my #2 choice.

By the numbers - Fuzzy Math:

I generally get Chevron Diesel at home with a 49 Cetane rating and likely at least a 520 micron HFRR lubricity rating. By adding Stanadyne my operating lubricity comes in around 363, which is great.

When I travel cross-country, I am much more likely to have to settle for fuels that have been untreated or been poorly treated, in addition to having woefully sub-spec Cetane ratings. Let's say I pull into the Gallup, NM, Pilot station on I-40 and fill-up with 40 Cetane. 725 micron garbage fuel. A 157 micron bump still would leave that fuel at an unacceptable 568 micron HFRR lubricity rating. A disaster waiting to happen. But if I instead add Opti-Lube XPD, the operating lubricity is around 406 microns, which is delightful and well within pump maker specs.

But there's a catch. Water. By using a demulsifier in a vehicle that lacks a water separator in the fuel filter, demulsified water (to the extent water is in my fuel and the demulsifier in the additive actually works) will collect in the bottom of the filter housing. Since both additives I've used contain demuslifiers, I've checked for water in the filter housing twice in 11k miles on my current vehicle and there's not been a drop of water in the housing. Some diesel enthusiasts in my area who also run demusifiers find about a half a teaspoon of water in the filter housing every 20k miles or so, but others find no water. My conclusion is that most of the fuel (at least Chevron which I run most often) is pretty well handled and stored and generally lacks water contamination.


Using demulsifiers in my vehicle that lacks a water separator is a worry because failure to detect and remove demulsified water in the fuel system (tank, filter housing, lines, etc.) isn't a good thing long term. Water sent through the injectors corrodes the injectors. Water in the fuel tank is a breeding ground for microbes. You don't want water in your fuel if at all possible.

Raw ULSD from the refiner is typically in the mid-600 microns range in lubricity. The stations samples with materially worse allegedly lubricity treated diesel likely had large scale gasoline and/or water contamination in their storage tanks on top of being too cheap/lazy to follow the law and pay the distributor to add lubricity additive to the raw fuel prior to delivery. Those numbers are nightmarish - criminal, really. Outright fraud on the buyer.


Let's face it. Hybrids suck. I put more than 140k miles on two of them commuting 180-240 miles round-trip per day for work. They are efficient, but sitting in the dentists chair getting a filling delivers more driving pleasure than driving a hybrid. They are souless, soul-sucking appliances for the automobile enthusiast. Enter the clean diesel. Our better-educated European kin have known about the supremacy of diesel for decades. In Europe diesels outsell both standard and hybrid gasoline vehicles. Europeans pay through the nose for fuel. They want to enjoy its consumption. Diesels are pure pleasure.

Diesel motors generate massive gobs of meaty, luscious torque right off the line. My VW TDI with hamster-displacement 2.0L motor nonetheless pumps out 236 ft-lbs of torque at 1500rpm. 0-70? Um, I wouldn't race for pinks. 0-30, Corvette URmyBICH. grin.gif And that's just a plain Jane VW station wagon with dual shift gearbox (automated manual). I'm a guy with a speed habit, so I am denied fast and furious vehicles forever more. So what'd I so? Bought the wife a FAST diesel.

Fast diesels? No such thing. Au contraire mon ami!

BMW has a high performance division called "M". It's like Mercedes' AMG, Ford's SVT, Nissan's NISMO, Honda's Mugen, Toyota's TRD, etc., etc. The 5 series is BMW's iconic mid-sized sedan. I've had a couple of them in the past. Great driver's cars. Krappy electronics. But I've never had an M series BMW. The M-series for the 5er is imaginatively called the M5. The M5 is NOT a diesel. The M5 has a 4.4L twin turbo V8 engine good for 560 horsepower and 680 ft-lbs of peak torque at 5750 rpm. But...at 1500 rpm, torque is "only" 500 ft-lbs. Torque is what launches a car from standstill. Horsepower is what defines it's top end speed and passing characteristics at speed.


She said "no" to an M5. I was saddened, as I've always wanted to drive one but never been so lucky. I have driven M3s and M6s though, but never owned one. I was also very relieved. The M5 with options runs about $100k. I wouldn't pay $100k for a car. Any car. Ever. She wanted to save the world with another diesel. So I bought her a 535d. 3.0L turbo diesel. Down 1.4L in displacement and one turbo to the M5 (one versus two). But...at 1500 it pumps out 413 ft-lbs of torque with peak torque of 560 ft-lbs at 3000 rpm.

0-60 in 5.8 seconds with an EPA rating (matched in real world driving; typical of diesels, not typical of gasoline or hybrid vehicles) of 26 city/38 highway.

No, it's no M5 (though it's a lot faster than my first 911). The M5 does 0-60 in 4.2 seconds. But it's a pig at the pump; EPA 14/20 - worse than my full-sized truck. The diesel 5-series is fast. Fast enough anyway. It's the second fastest 5 series after the M5, in fact, and by far the most efficient. Who says you can't have your cake and eat it too? Well I can't. I rarely get to beat on it. But my wife can have her cake and eat it too, courtesy of your friend, the CLEAN DIESEL.

My lesser diesel is rated at 28/39 and my commute is almost 100% stop and go (1 hour for 21 miles). My lifetime commute average is 36mpg. My highway trip average is 45mpg usually achieved between 75 and 85mph. It didn't break the bank, holds as much as a Forester, CR-V or 4Runner, handles better than most cars in its price range, is quiet, comfortable, has a nice interior and has lots of useful features not available on other vehicles in its class. To me the extra learning and measures to correct for our lousy quality ULSD fuel in the States are well worth the rewards.

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Good points and bad here, some true, some not.


biodiesel made from corn - no, corn makes ethanol (gas) biodiesel comes from many OIL based items - vegetable oil, waste cooking oil, soy, etc - http://en.wikipedia.org/wiki/Biodiesel#Biodiesel_feedstocks


USLD has less lubricity then dinodiesel - true - distributors are suppose to add additives to replace it - true - survey says - 30% of the time it was not added (have to dig up an old reference. I add a lubricity / cetane modifier at every tank. I use dry gas also, when I run gas engines, and fuel stabilizers now.


Water in the fuel is bad - true - corrosive - true - I'll venture to say that 95% of the diesel vehicles out there have water separators - BUT, they can be overcome by way to much water to quickly - hint - so can gas engines - fuel line freeze up anyone.


I'm not racing so fast starts, eye burning burnouts, are not part of my thing. I'm pulling a trailer. A buddy of mine is into that, and his diesel will roll coal, and light all 4 tires up (4x4) when he wants to. His dyno is 500+ hp and 1000+ ft/lbs torque and he can spin his clutch in a heartbeat.(overpower).


Just saying, some issues, some not, and for what we're doing, use a big grain of salt.

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What he said is pretty much true. And, it costs more to refine Diesel now that we have to run ULSD.

I run a 1996 Dodge with the Cummins Diesel, the fuel system in it is old fashioned, not the high pressure of the new ones.

My Dodge has over 420,000 miles on it and I have not done anything major to the engine (one head gasket at about 130,000 miles).

I used to go to Alaska a lot in that PU so due to the cold (Below 0 a lot) it idled a lot to keep it running, so it has a lot of hours on it for the miles driven.


The additives I use now on the fuel I buy is

1. 2 cycle motor oil, the good stuff, sythetic, about a pint to 40 gallons.

2. Biocide, I do not want algae growing in my fuel.


The 2 cycle motor oil takes care of lubricity problems, that is what I am most concerned about with the fuel we buy now.

The cetane level can be tuned for in the engine, my injection system is mechanical and it is tuned for the cetane I can buy now.

The fuel mileage suffers some if the cetane is low.


My system works for my truck, it still runs better than new and I can go 10,000 miles on a oil change and never add any oil.

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When the low sulphur fuels came out, the injection pumps on many diesels started failing. The homemade remedy was to add a little 2 stroke oil to your fuel to put a little lubricity back in it. The VP-44 pumps that were on the Cummins, were fuel lubricated pumps that needed the sulphur to keep it smooth.

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