The Cost of Poor Fuel Quality
Dirt. It is all around us. It is in the food we eat, the clothes we wear, and the fuel our vehicles burn. In small enough quantities, we don't even notice it. But what "small" means depends on the system exposed to it. And what is dirty to one thing, may not be dirty to another. All that aside, we want this article to focus on your fuel and what it means to your engine.
The precision involved in manufacturing diesel fuel injection is by necessity, important. The close tolerances are necessary because we are trying to keep a liquid moving, between two steel parts, without that liquid going just anywhere it wants to. Consequently, parts are made so that a molecule of diesel fuel will have a tough time squeezing between what is essentially a doorway to a path we don't want, and one that we do want it to go through. If you think about an elevator in a building, when you step through, in or out of the elevator, you are that molecule. The elevator is intentionally designed so that you can only get into the elevator, and not the elevator shaft. Imagine if you had to step over a 3 foot wide gap between the elevator and the building floor. You would have a choice, albeit an unwise one to make poorly. You could get into the elevator car, or the elevator shaft. As the designer of the elevator, you would know this, so that gap between the elevator car and the surrounding doorway in the building has to be small. Now imagine, that you have a big rock with you. One that IS ALMOST small enough to fit between the elevator and the shaft it is in. Now that rock thinks it does have two choices, especially since the elevator is crowded and full of people. It decides that instead of getting in the car with all the people, it is going to wedge itself in the gap between the elevator car and the elevator shaft. When the elevator moves, it rolls and its irregular shape allows it to rotate to its widest part as it does so, and now the prying force between the elevator car and the walls of the elevator shaft is jamming the car in the shaft and it can't move. The elevator cables snap from the force being exerted to pull it up, and now we have a very broken elevator.
In the photos below we see the drive train of a rotary pump, in this case, a Stanadyne DB2 for a Chevy application. The drive shaft attached to the drive gear in the engine is on the left, and the hydraulic head and rotor assembly is on the right. In the first picture, the representation is as it would look when operating. In the subsequent photos we see what happens when our proverbial rock of dirt rolls over and causes chaos. The prying force it exerts causes metal on metal contact that normally does not occur. Since the rotor (the center part shown by the cut-away of the head) is turning at a high rate of speed, the resulting friction between the two parts causes a rapid swelling of the rotor. More swelling means more contact, and in a very very short time, the rotor has swollen to the point where it is essentially a brake shoe instead of a rotor, and it grabs the inside of the head with enough force to stop it. This stops the injection of fuel, and the engine shuts off like you just turned the ignition key to off. Of course, when you have 400 or more foot pounds of force being exerted on the pump drive shaft, the momentum is going to insist that it keep turning. The engineers at Stanadyne knew that, so they designed the drive shaft with an intentionally thinner region, which by design, now twists off. This saves your engine gear train from damage. The injection pump, however, is now junk. It's head and rotor welded together, and the driveshaft snapped. These are the two absolutely most expensive parts in the pump, and it is not good as a core, but it will make a great door stop.
While our example is of a rotary pump, the same holds true for an in-line pump or any hydraulic system. When two parts become firmly connected together when they are supposed to be moving, bad things are going to happen, and things are going to get expensive. So how do we prevent this? Well, our species has been asking this question ever since we invented this stuff. We do a lot of things towards that goal. Filtration has been the biggest servant. Kind of like a security guard at the entrance to a building who knows to look for rocks, these filters remove and capture most of the bad things. But they can't get rid of them. They can only detain them, which means unless you replace the filter frequently, your little rock jail is getting more and more crowded every time you operate your equipment.
Everyone is aware that prison over-crowding has been shown to be bad for society, and a full filter is bad for your equipment. But you can't tell how full a filter is, generally, by looking at the outside of it. If someone pours a bag of sand in your fuel tank, that filter is going to be full THAT DAY or the first hour of operation. But if you don't know the sand is in there, now you drive around for months or years with that bag of sand just itching to get through to your pump. But of course, we can't replace a filter every day. That's unrealistic. Only you can decide how often to replace it. Generally speaking, at Moose Diesel, our philosophy is to go half the miles, the hours, or the time that a manufacturer recommends. We don't always trust those folks. They have a predisposition to want to sell you a new machine sooner, rather then later. Their recommendations are often designed to get you through the warranty period without issue, but after that... who knows. We like our stuff to last a really long time, and filter changes are cheap insurance.
Little rocks of course, are not the only issue we deal with. While the parts of an injection pump or injector generally try not to rub together, there are some that by design do, and so lubrication is key. Rubbing means wear, and the main way to fight against wear is to remove as much friction as possible, and this is done with a quality fuel additive. Unfortunately, today's fuels are not designed that much with lubrication (referred to as lubricity in a fuel) in mind. There are minimum tests that fuels must pass to get certification, but these specifications are designed these days for common rail engines that have fewer moving parts. As engine oil viscosity has dropped in recent years, in a move to improve fuel economy, diesel fuel quality has also diminished. The lubricity removed when sulfur was removed from diesel fuel has never returned to the prior era, and older fuel injection systems have been left with a fuel for which they were not actually designed. This makes a fuel additive extremely important.
So filters, and fuel additives are our front line against bad stuff happening to our fuel injection systems. What else can be done? Well, water needs to be kept out. As does algae. This means keeping your fuel stored properly. If you every see a brown or black slime in your fuel system, you've got algae contamination and a biocide needs to be introduced to the fuel to combat this. Fuel tanks go for decades, usually with complete neglect, so occasionally removing them and giving them a thorough cleaning is of benefit. Fuel lines also can degrade. Rubber hose in particular can begin to shed particles if the inside of it begins to deteriorate, so replacing fuel line can be a wise move.
All of this relates to a closed, and in-service fuel system. Often times though, YOU can be the biggest risk to your fuel system. Many technicians with good intensions have inadvertently allowed dirt to enter a brand new fuel system component, simply by not being cautious or taking care. BEFORE servicing a fuel system, always... ALWAYS... clean the outside of the engine. This can be difficult, particularly if it is broken down and somewhere less then convenient, but remember that dirt we talked about at the beginning of this article? Yeah it is in your skin. On your fingers, your tools. Clean everything, wear new surgical gloves. Use compressed air to blow away any remaining dirt and then when you put your wrench on and break that connection loose... don't unscrew it all the way just yet. Use the compressed air to blow away the dirt that was hiding in that joint that you just started to expose.
With luck, and wisdom on your side, the chances of having issues with your machine will be greatly reduced, and long life and prosperity will be in the offing!
Some things to remember about filters. All filters have 3 numbers associated with them. An Absolute, and a nominal micron rating, and a percentage. The absolute is the number they don't usually give you. It is the largest particle size that will pass through the filter. Period. The nominal rating is the advertised Micron rating. That is the smallest particle that the filter will filter down to. The percentage is the relationship between the two. Let's look at two filters, both serving a fuel system with a 10 gallon tank. We will assume also, that in our example, the fuel system recirculates the fuel. That is, the unused fuel from the injection process, goes back to the tank.
So we go to a store and we find two filters to choose from. One says it is a 6 micron filter and one is an 8 micron filter. The 8 micron is strangely more expensive, so naturally we want the 6 micron filter, and hey! It's cheaper! We buy it and think we have done a good job. But did we? If you researched it, you may find that your 6 micron filter has an absolute rating of 30 and a percentage of 50. Well, that means on the first pass of that 10 gallons of fuel going through that filter, only 5 gallons is going to be filtered down to 6 microns. The other 5 gallons will be between 6 and 30. 30? My goodness, that sounds like a rock in an elevator shaft! But what about that 8 micron filter? Well, it has an absolute rating of 20, and a percentage of 60. That means that 6 gallons will be filtered down to 8 microns, but only 4 gallons will be between that and 20. Of course, we have a recirculating fuel system, so provided that we don't add any new fuel, all 10 gallons will eventually be that smaller number. But how many times did that 20 or 30 micron rock have a chance not to get in that elevator? This is why filter selection requires thought and don't shop just by price.
We hope this information has helped you make better choices for your engine, and thanks for shopping at Moose Diesel!