With today’s fuel prices, it’s helpful to be familiar with the workings of your motorhome’s diesel engine, plus know how to conserve and keep more dollars in your wallet.
By Jim Brightly, F358406
As fuel prices have gone up, interest in better fuel mileage has kept pace. Plus, concern over reducing America’s dependency on foreign oil is also increasing. Even the Bush administration is promoting the wider use of both diesel and biodiesel fuel. At the FMCA international convention in Pomona, California, this past March, both diesel seminars I moderated included many questions from attendees about the use of biodiesel in motorhome engines.
These concerns expressed by FMCA members have spurred the writing of this article. Many of the ideas and suggestions herein you’ve heard before, but this article may focus your attention more clearly.
According to Cummins Inc., C4251, use of biodiesel fuel has grown dramatically from just 500,000 gallons in 1999 to 30 million gallons in 2004. The U.S. Department of Energy is forecasting a fast growth in production capacity beyond that. But before you fill your tank with biodiesel, ask yourself, “Do I really want to save a few dollars per tank at the possible expense of a $10,000 to $20,000 engine?”
The short answer is: Perhaps, as long as you limit your use of biodiesel to the B5 blend. B5 is a fuel blend of 5 percent pure biodiesel with 95 percent standard petroleum diesel. No modification to the engine is needed to enable it to operate on B5 biodiesel, and no impact on engine performance, durability, or maintenance is anticipated with its use. However, users of B5 biodiesel should ensure that the fuel is of a consistent, high quality appropriate for that of a high-performance diesel engine. (B5 is approved for use in RV engines manufactured by Cummins and Detroit Diesel. Caterpillar actually allows up to B30; however, Caterpillar officials suggest that owners refer to the Caterpillar Commercial Diesel Engine Fluids Recommendations bulletin — SEBU6251-09 — to better understand the requirements.)
The reasons higher percentages of biodiesel are not approved are simple. Actually, they are threefold. The first concern is the lack of an industry fuel standard for biodiesel in terms of fuel consistency and stability, which has resulted in product performance issues such as fuel filters becoming plugged. This becomes essential when moving beyond the relatively low blend level of B5. All three manufacturers wish to ensure that their engines will continue to offer the same high levels of performance and dependability RV customers have come to expect.
The second reason is the cost of engine replacement should unanticipated problems arise from using B20 or higher-percentage blends. It’s much, much better for all concerned to be safe rather than sorry. Currently, all three RV engine manufacturers are conducting extensive over-the-road testing with their engines.
Third in the list is meeting the 2007 Environmental Protection Agency (EPA) requirement for clean air emissions in combination with the introduction of ultra-low-sulfur diesel (ULSD). As the engines for all three manufacturers will be essentially the same as current products, they will continue to offer B5 biodiesel capability in 2007 models. The B5 biodiesel fuel used with the 2007 engines will need to conform to the same 15-parts-per-million sulfur content level as the ULSD fuel to ensure that there is no adverse effect on the various methods the companies are using to keep the exhaust gases clean.
Is biodiesel more environmentally friendly than standard diesel? In terms of exhaust emissions from the engine, the use of biodiesel at various blend levels is not yet fully understood — hence the exhaustive over-the-road testing that is being conducted. There are indications that particulate matter (PM) and hydrocarbon (HC) emissions may be reduced — but oxides of nitrogen (NOx) levels may be marginally increased. Therefore, the overall exhaust emissions impact of using biodiesel may prove to be very close to that of using standard diesel.
The major benefit of using biodiesel is that it is environmentally sustainable. As a natural substance, mostly derived from soybeans and other oil seed crops, it is renewable and biodegradable. Biodiesel also offers an opportunity to reduce the nation’s dependency on imported oil and ensure greater energy security. As President Bush said recently, “Every time we use homegrown biodiesel, we support American farmers, not foreign oil producers.”
Will biodiesel affect your engine warranty? Again according to Cummins, “The use of biodiesel does not affect the Cummins materials and workmanship warranty. However, any engine failure or performance issue caused by the use of biodiesel or other fuel additives cannot be considered as defects of the Cummins engine, components, or workmanship — and would, therefore, not be covered by Cummins warranty.”
I will get into extending the mileage range of your fuel tank, but first a bit of basic information about the diesel engine. Unlike a gasoline engine, which can be turned off by shutting down the ignition’s electricity, a diesel has no electronic ignition per se, so it can’t merely be “shut off.” A diesel must be turned off by shutting off its fuel supply — basically that means turning off the fuel pump and stopping the fuel flow.
Modern diesel engines, however, are “controlled” by very sophisticated electronics, and they meter the fuel injections to the nth degree. A diesel engine gets its power from what is called “compression ignition,” in which the fuel-air mixture is fired by being compressed by the piston. Since most RV diesel engines are considered “four stroke” engines — much like a gasoline engine — let me take you through a firing sequence of a single cylinder:
a. The piston is pulled downward by the rotation of the crankshaft, which creates a near vacuum in the cylinder; the intake valve opens.
b. The turbocharger shoots in its charge of air at a much higher pressure than the ambient air pressure (this is why turbodiesels are much less affected by high altitude than normally aspirated engines).
c. As the crankshaft pushes the piston upward, the air is compressed, which causes it to become superheated.
d. As the piston moves upward in the sealed cylinder, the air is compressed by the piston; this quickly superheats the air to temperatures and pressures critical for ignition when fuel is injected.
e. In a matter of microseconds, the fuel is injected in three pulses; each pulse is critically timed electronically. For want of better terms, they could be called “pre-ignition, present-ignition, and post-ignition.” The pre-ignition pulse is fired, then the present-ignition pulse is added to the mix, and then the post-ignition is injected just as the piston begins its downward power stroke for an added boost, much like an afterburner in a jet plane. This triple-pulse is one of the reasons modern diesel engines are much quieter than their predecessors.
f. When the crankshaft pushes the piston upward again, the exhaust valve opens and the exhaust gases are pushed out of the cylinder. (And then the whole sequence starts over again.)
The heat of compression is what ignites the diesel fuel-air mixture. In extremely cold temperatures, the heat of compression may be insufficient to ignite the fuel that is injected into the cylinder. This is one of the reasons diesel engines require block heaters, whereas gasoline engines do not. In very cold weather, without heated cylinders, it may take several rotations before the cylinder pressures and temperatures reach the critical point for ignition, which will cause excessive exhaust smoke (much like a “flooded” gasoline engine). As the engine ages, clearances wear and become larger, causing less efficiency, exhaust smoke, and hard starting.
Now that you know how your engine works, you can watch the rpm readings on your tachometer while driving down the highway and realize that for every one of the 1,200 to 1,800 revolutions per minute (rpm) your engine is going through its full four strokes. In other words, at 1,200 rpm, all four cylinder movements are occurring 600 times each minute! In each cylinder!
IMPROVING OPERATION, FUEL ECONOMY
Now let’s get into extending engine reliability and fuel mileage. We all have heard the campground warm-up drill in the early morning hours. There’s always at least one diesel owner who thinks he has to warm up the engine until it’s at full operating temperature before he can move the coach. First thing he does is start his engine — he hasn’t even finished his first cup of coffee, but his engine is running. Then, he proceeds to disconnect his shore power and hoses. Meanwhile, his neighbors up to six sites away are also forced to get up because of the engine’s noise. Be a good neighbor, even if you’re pulling out; empty your holding tanks, disconnect all hoses and electrical connections, then start your engine. Allow it to warm up and pressurize your air brake system while you do your final walk-around. Visually check to make sure all of your awnings are in their stored positions, your TV antenna is down, all jacks are up and locked, and your towed vehicle is ready to roll. This should take you about five to seven minutes (a few minutes more if you have to pull out of the site to hook up your towable). It is all the time you need to warm up your engine and charge your air tank. Any additional idle time merely wastes fuel, adds unnecessary wear to your engine, and annoys your neighbors.
While you’re stuck in a campground’s registration line, kill your engine. You may think you’re doing your engine a favor by allowing it to cool down after pavement pounding all day, but that’s not so. Again, it’s a waste of fuel and engine wear. The turbo cooldown took place while you were still on the off-ramp or waiting for the cross traffic at the stop sign. No additional cooldown time is needed and is just wasteful. Give the other registering folks a break, and shut down while in the line.
INSPECTIONS AND PREVENTIVE MAINTENANCE
Most of us grew up in an era when maintaining our own cars and trucks was a sign of pride in ownership, and we try to carry that over into maintaining our coaches. The task is a bit more daunting, however, with a diesel pusher. At the most, that gas-burning V-8 held only six quarts of oil with a filter. Today’s diesel motorhome engines hold three to five times that amount of oil. The reality of changing one’s own oil involves more than cost. The cost of just the oil will save you some money, although having to find a safe and ecological location for disposing of the waste oil could create problems of its own. In addition, having a professional factory-trained technician maintain your coach could save you a bundle in the long haul.
While you could change the oil, the trained eye of a technician familiar with your chassis could perhaps discover a problem in the making long before it becomes a major headache. Remember, breakdowns do not occur while your coach is parked in your storage lot; they happen on the road. A trained technician might spot the signs of wear, whereas you may not even know what you were seeing if it reached out and bit you.
If you decide to perform your own work, definitely do not use cut-rate filters. Always stick with your engine manufacturer’s recommendations. These recommendations are based on many, many years of experience with long-haul trucks, RVs, and heavy-duty applications. After all, where’s the logic in saving $2 per filter on an engine that could cost you between $10,000 and $20,000 to repair?
Know this: regular inspections pay off! Set up a schedule for inspections. While traveling, you’ll need to do some inspections daily, some weekly, some monthly, and others on different time schedules. In order to keep all the inspections straight in your head, you’ll need an established routine (perhaps even a checklist). When traveling, set a daily routine. Check the engine oil level, but don’t keep adding oil to make it reach the full mark each day. Your engine will find its own “comfort zone” for oil level, so keep the level between the “add” and “full” marks. Don’t forget to check the oil reservoir if your engine is equipped with one. Remember, use only factory-approved oil, which should be the same brand and weight that’s already in the engine.
Check your air cleaner daily, especially if you are driving in dusty areas. Replace only with the correct factory-approved filter. Check all belts and hoses for checks, cracks, leaks, etc., weekly.
Check your batteries, their connections, and the cables monthly for corrosion. Clean if necessary or, if you don’t feel competent to do this, make a note to have the technician perform this task at your next scheduled maintenance visit.
As little as 10 minutes a day in preventive maintenance will leave you with peace of mind to better enjoy your motorhome.
When it comes to coolants, always stick with your engine manufacturer’s recommendations. Again, these recommendations are based on years of experience with long-haul truckers, and using the wrong product could result in a hefty repair bill.
Supplemental coolant additives (or SCAs) are chemicals (usually molybdates and nitrites) that form an invisible barrier on the surfaces of coolant passages inside the engine. They provide protection from liner pitting, mineral scaling, oil fouling, deposits, rust, and general corrosion. In some engines, they are not needed. In others, they protect the engine against damage due to cavitation (erosion or pitting of the cylinder linings). Check your owners manual to be sure.
Top off the cooling system with distilled water, not tap water. If you’re using extended-life coolant, top off using only extended-life coolant.
Do you need a coolant filter? The short answer is, possibly. It depends on your engine’s design. Coolant filters remove any solids that may appear in the coolant system (a survey found that 40 percent of the used coolant filters checked contained moderate amounts of contaminants, and 10 percent contained heavy contaminant levels). Filters reduce engine wear, corrosion, pitting, and passage obstructions. They reduce scale formation, which maintains a more effective heat transfer, and filters can extend coolant life. It has been found that coolant filters also reduce water pump seal damage and leaks. Check your owners manual to determine whether your engine design incorporates a coolant filter.
If you have more questions, one good way to have them answered is to attend the next FMCA international convention and ask the experts yourself at the diesel owners’ seminars. If the question has to be answered as soon as possible, your owners manual will have a toll-free number for customer service.
10-Minute Preventative Maintenance Inspection
- Check the engine oil level.
- Top off the cooling system.
- Check the air filter.
- Check all belts and hoses for leaks and cracks.
- Check batteries, connections, and cables.
- Check battery cables for corrosion.
Diesel Engine Manufacturers
Caterpillar Inc., C4743
Cummins Inc., C4251
(800) DIESELS (343-7357)
Detroit Diesel, C4620