Many motorhomers believe these “mobile legends” about diesel engines to be true. But are they?
By Jim Brightly
Technical Editor
February 2003
During FMCA’s 27th annual winter international convention in Perry, Georgia, in March 2002, I had the opportunity to sit down with Chuck Goode of Cummins Engine, C4251, and Mike Meloche of Detroit Diesel, C4620, and talk about some of the common questions and misconceptions related to diesel engines.
The following information applies to most turbocharged diesel motorhome engines, regardless of the manufacturer, and addresses some of the more common questions and myths associated with these power plants. If you’re a diesel owner, see how well you do answering these questions.
Warm-up
Q: Should a turbocharged diesel engine be fully warmed up to its operating temperature before being driven?
A: We’ve all heard –; literally –; this early-morning drill. There’s usually at least one diesel owner who thinks the engine must be warmed up to its full operating temperature before the motorhome can be moved out of the campsite. First, the owner starts the engine –; even before finishing that first cup of coffee –; and then proceeds to disconnect the shore power and hoses. Meanwhile, his campground neighbors are stirred from their sleep because of the engine’s noise.
The best advice is to be a good neighbor –; even if you’re pulling out –; by emptying your holding tanks and disconnecting all hoses and electrical connections before you start the engine. Allow the engine to warm up and your air brake system to pressurize while you do your final walkaround. Visually check to make sure all 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 approximately five to seven minutes –; all the time your engine needs to warm up and the air tank to charge. Any additional idling time merely wastes fuel, adds unnecessary wear to your engine, and annoys your neighbors.
Cooldown
Q: Is it necessary to idle the engine for a period of time to allow the turbocharger to cool before shutting it down?
A: We’ve all been stuck in a campground registration line breathing hot diesel fumes from the motorhome ahead of us. The owner, who believes that cooling down the engine in this manner is beneficial to the turbocharger, is busy signing in and buying groceries. Eventually, the owner returns to drive the motorhome to its campsite.
Our diesel experts, however, said cooling the engine in this manner is completely unnecessary. In fact, they contend that the turbocharger will sufficiently cool when the motorhome slows on the highway exit or while it waits for traffic to clear at a stop sign. No additional cooldown time is needed. So, turn off the engine and save some fuel.
Engine Idling
Q: Since diesel engines get such good fuel mileage, use virtually no fuel when idling, and take so long to start (which uses more fuel), isn’t it better to leave the engine idling when parked rather than shut it down and restart it again when needed?
A: It’s not uncommon to see long-haul trucks parked at truck stops or rest areas for the night with their engines idling. So you ask yourself, “If truckers do it, why shouldn’t motorhomers?”
The difference is that most truckers don’t buy their truck’s fuel –; the owners do. In addition, the drivers don’t pay for engine repairs –; the owners do. Also, in some cases, owners gauge a driver’s performance by engine hours used rather than the route. In such instances, a driver can sleep longer (with the engine running) and drive faster to make their scheduled arrival. All that matters to the owner is how much time the engine has been operating.
Since a motorhomer buys his or her own fuel and pays all maintenance and repair costs, it behooves the owner to shut the diesel engine down and start it up as needed.
Oil Changes
Q: Is it more economical for the owner to change the engine oil than to take it to a technician at the engine manufacturer’s local maintenance shop?
A: Yes and no. Many of us grew up in an era when maintaining our own cars and trucks was a sign of pride, and many of us continue that tradition by maintaining our motorhomes. However, the task of changing the oil in a diesel-pusher motorhome is a bit more daunting. At most, your gas-burning V-8 engine held only six quarts of oil with a filter. Today’s diesel-powered motorhome engines can hold three to five times that amount of oil.
The reality of changing one’s own oil involves more than cost. Sure, you can save a few dollars if the only thing you take into account is the cost of the oil. But other considerations also come into play –; for example, finding a safe and ecological location to discard the waste oil. Having a professional factory-trained technician maintain your coach could save you a much larger amount of money and aggravation over the long haul.
The trained eye of a technician can discover a mechanical problem in the making long before it becomes a major headache. Remember, breakdowns don’t typically occur while your coach is parked in the storage lot; they happen on the road. A trained technician may be able to spot signs of wear that you would completely miss.
Oil Filters
Q: Is it all right to use filters other than what the owners manual recommends? I can save $2 by using a different filter.
A: Always stick with your engine manufacturer’s recommendations. These recommendations are based on many years of experience with long-haul truckers and heavy-duty applications. After all, is it better to save $2 per filter on an engine that could eventually cost you between $10,000 and $20,000 to repair, or to spend the couple extra dollars?
Regular Inspections
Q: How important are regular inspections and preventive maintenance?
A: According to our experts, establishing a routine inspection and preventive maintenance schedule is one of the best things you can do for your diesel engine. If necessary, create a checklist for daily, weekly, monthly, and other inspections. Here are a few points to include on your list:
- Check the engine oil level daily when you’re traveling, but don’t keep adding oil to make it reach the full mark each time. Your engine will find its own oil level comfort zone, so just make sure the level stays between the “add” and “full” marks. And 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.
- Top off the cooling system with the recommended coolant/distilled water mix. Do not use tap water. If you’re using extended-life coolant, top off only with that.
- Check the engine’s 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 fraying, cracks, leaks, etc. on a weekly basis.
- Each month, check your batteries, their connections, and the cables for corrosion. Clean if necessary. If you feel uncomfortable doing this, make a note to have the technician perform this task at your next scheduled maintenance visit.
Just 10 minutes a day of performing preventive maintenance will give you the peace of mind to better enjoy your motorhome.
Synthetic Lubricants
Q: Is it all right to use synthetic lubricants that promise to last twice as long as regular motor oil?
A: Always stick with your engine manufacturer’s recommendations, which are based on many years’ experience with long-haul truckers and heavy-duty applications. Again, is it worth saving a few dollars and a little bit of time on an engine that could cost you between $10,000 and $20,000 to repair?
Supplemental Cooling Additives
Q: Do diesel engines really need supplemental coolant additives (SCAs)? Doesn’t the coolant recommended by the engine manufacturer do an adequate job of protecting the coolant system?
A: Supplemental coolant additives are chemicals (nitrites, phosphates, and molybdates) that form an invisible barrier on the surfaces of coolant passages inside the engine. An SCA provides protection from liner pitting, mineral scaling, oil fouling, deposits, rust, and general corrosion throughout the coolant system. In some engines, SCAs are not needed; in others, they protect against cavitation damage (erosion or pitting of the cylinder linings). Check your owners manual to be sure.
Coolant Filters
Q: Are coolant filters really necessary or a waste of money?
A: Coolant filters remove any solids that may appear in the coolant system. According to one diesel engine manufacturer, 40 percent of the used coolant filters checked in a particular survey contained moderate amounts of contaminants, and 10 percent contained heavy contaminant levels. Coolant filters reduce engine wear, corrosion, pitting, and passage obstructions. Filters will reduce scale formation in the system –; allowing it to transfer heat more efficiently –; and can extend coolant life. The use of coolant filters also has been found to reduce water pump seal damage and leaks.
How did you do?
If you’re a diesel owner and you knew the correct answers to all of the preceding questions, pat yourself on the back. If you didn’t, pull out your owners manual and brush up on your diesel knowledge.
If you have other questions about operating and maintaining your diesel engine, I encourage you to attend FMCA’s 69th International Convention, March 21, 22, and 23, in Pomona, California, or another future convention. There you can talk face-to-face with diesel engine experts at the diesel owners’ seminars. If your question has to be answered immediately, consult your owners manual for a customer service telephone number to call.