Keep your motorhome’s moving parts operating at peak efficiency by selecting the proper lubricants and following a regular service schedule.
By Mark Quasius, F333630
November 2012
A motorhome chassis contains hundreds of moving pieces. The engine, transmission, axles, and other parts that help to propel these large vehicles down the road all require lubrication to keep everything in working order. Each component has its own unique job to perform, and the lubrication required to facilitate its operation varies greatly. Using the wrong lubricant or failing to maintain adequate lubrication levels or service intervals will result in expensive repair bills.
Fortunately, lubricants are designated with a series of American Petroleum Institute (API) or military (MIL) category numbers that identify their suitability for various applications. Choosing the proper lubricant involves reading your motorhome chassis owners manual to determine the API service level required, and then matching the lubricant’s viscosity and rating to the specifications that relate to the motorhome’s operating environment.
Ratings
Two types of ratings apply to any lubricant — viscosity and quality. Viscosity is just another term for thickness. Every engine is designed to utilize a specific oil viscosity for any given set of operating conditions. For this reason, oils are rated by the Society of Automotive Engineers (SAE) according to a standardized numerical rating. All you have to do is consult the owners manual to determine the oil viscosity that should be used for the engine in a particular climate, and then match it with a product at your local auto parts store or service center.
The quality of oil is determined by its chemical makeup and its imbedded additive package. The American Petroleum Institute has established the API rating system to identify oil quality, and both the API and SAE ratings will be marked on every container. Once again, consult your owners manual for the minimum API rating specified for your engine. Note that you can always exceed the API ratings and use a better grade of oil, but you should never use oil that is lower than the minimum API rating specified.
Viscosity
The SAE ratings of a lubricant will identify its viscosity. The larger the viscosity number, the thicker (heavier) the oil. For example, SAE 40 oil will be heavier than SAE 30 oil, while SAE 10 oil will be significantly lighter. The viscosity determines the ability of the oil to flow at a given temperature. As oil heats up, it thins out, flows faster, and doesn’t provide the same level of lubrication as thicker oil. If the oil is too thick, it won’t flow fast enough to provide lubrication for the critical components it’s supposed to protect. SAE ratings reflect the ability of the oil to flow at 210 degrees Fahrenheit; that rating can be useful when determining how oil will perform in summer use.
The SAE ratings referenced above do not take into account the low-temperature performance of the oil, which reflects winter use. A second test is taken at 0 degrees Fahrenheit to rate an oil designed for winter use, and these ratings are given the “W” rating. For example, SAE 10W oil is thinner than SAE 20W oil, but both are designed for winter use.
The majority of the wear and tear on any engine occurs during startup. During those first few seconds of ignition, the engine turns over and begins to fire, but all of the moving parts are cold, and the pistons haven’t yet expanded to their design tolerances. The oil begins to flow, but by the time it is pumped to all of the critical areas, the engine has been running for a few seconds. Using lighter-weight oil helps in that regard, because the oil pressure comes up much faster than when using thicker oil. However, once the engine is working under a heavy load, thinner oil will become too thin and will not provide adequate lubrication. So, you wind up using a heavier oil and live with the startup wear rather than using a lighter oil and paying the penalty when the engine is working really hard.
Multiviscosity oils are a huge improvement in that area. A multiviscosity oil has dual ratings. A 10W-30 oil will have the low-temperature performance of 10W winter oil, yet it retains the high-temperature performance of an SAE 30 summer oil once the engine reaches its operating temperature. This gives you the best of both worlds and does a better job of protecting the engine at both startup and when under load.
Engine Oil API Rating
Modern engines are fitted with extremely close tolerances compared to older power plants, because of improvements in fuel economy and stricter emissions requirements. The same motor oil that was used in a 1990 model-year engine won’t be effective in today’s engines. The owners manual for your motorhome’s specific engine will detail the minimum API rating oil that should be used. Gasoline engines use the “S” (service) series of ratings, while diesel engines use the “C” (commercial) series of ratings.
One important consideration for owners of diesel engines that fall within the EPA’s “2007 Highway Rule” is the CJ-4 rating. Motorhomes using the new EPA-2007 spec engines generally began showing up in the 2008 model year. The new emissions requirements mandated use of ultra-low-sulfur diesel (ULSD) fuel because of the diesel particulate filters (DPF) that were added to the emissions controls. The DPF was susceptible to fouling by any contaminants, such as sulfur, and required ULSD fuel with less than 500 ppm of sulfur. Motor oil contained levels of zinc as an antiwear additive, but the DPF also became fouled by levels of zinc that would be present in the exhaust. So, a new motor oil was designed for use with these engines. This oil was the API CJ-4 specification. The zinc was removed from the oil and replaced with other antiwear compounds that won’t leave ash content in the DPF. Owners of an EPA-2007 diesel engine must be sure to choose API CJ-4 oil when performing oil changes.
A Case Study For Synthetic
Conventional motor oil is formulated from crude oil that is pumped from the ground and contains impurities such as sulfur, wax, and asphalt. Because conventional oil is “found” rather than “created,” its makeup is somewhat inconsistent. Synthetic oil is chemically created in controlled laboratory conditions, which eliminates any impurities and provides for molecules that are consistent in size and shape. Because synthetic oil is fabricated, it can be fine-tuned to have just about any properties the chemist chooses to incorporate. Synthetics have the ability to flow at much lower temperatures than conventional oil, which greatly improves cold-weather performance without diminishing high-end performance. It’s common to find a conventional oil that’s rated at 15W-40 that can be replaced by a synthetic oil of 5W-40.
All oil will boil once it gets hot enough and will vaporize and harden as carbon deposits once it hits hot spots within the engine, such as the area immediately above the top piston ring. This carbon buildup accelerates wear on the cylinder wall. Another problem area is the turbocharger oil galleries, where oil cokes up and plugs the critical pathways that supply oil to prevent failure of the turbocharger bearings. If this buildup continues, the flow will be restricted and the engine will experience premature turbocharger failure. Conventional oil tends to break down at approximately 250 degrees Fahrenheit, but synthetics typically remain stable at 290 degrees and beyond, so these issues won’t be as prevalent as with conventional oil.
| Allison Transmission Approved Product Listing Click chart to enlarge |
 |
Synthetic oil manufacturers claim that you can extend your service intervals when compared to conventional oil. However, not every engine manufacturer states the same, so you may not be able to do that without voiding your engine’s warranty. Most motorhome owners change their oil based on time rather than mileage, because their engines aren’t used as often.
Because of the increased cost of synthetic oil, the idea of saving money by extending service intervals may or may not apply. However, synthetic oil will give your engine better protection. Cold starts and operation in cold weather will be easier with synthetics because of the lower flow temperature of the oil. The increased boiling point of synthetic oil also will ensure that you have an edge on protection during those times when your engine is working really hard.
Automatic Transmission Fluids
Automatic transmission fluid (ATF) differs from engine oil. Engine oil is designed to lubricate bearing surfaces that are under compression, and it has detergent and additive packages to help clean the engine and trap combustion deposits that can be removed in the oil filter. ATF is designed to lubricate fast-turning shafts and clutch packs; to transfer power through a complex system of servos, pumps, and fluid couplings; and is the primary method of cooling the transmission. Because these needs are vastly different, so are the lubricants designed to protect them. The ratings used for ATF are also different, so SAE and API ratings do not apply.
If you own a Type B or a Type C motorhome, chances are you have a Ford or Chevrolet transmission in it. These transmissions utilize the Dexron or Mercon variants of automatic transmission fluid that are available on auto parts shelves almost anywhere. But most Type A motorhomes come equipped with the ever-popular Allison automatic transmissions. Allison transmissions can be filled with the same Dexron ATF that you run in your Chevy pickup truck, but it’s highly recommended to use synthetic ATF to provide the best protection and extend the service intervals. In fact, at some point during the 2004 model year, both Freightliner and Spartan began shipping their chassis prefilled with Allison’s synthetic TranSynd fluid. Synthetic fluid benefits transmissions greatly and raises the temperature at which the fluid will burn during hard use.
The biggest question with Allison owners is whether they need to find Allison’s TranSynd synthetic transmission fluid, or whether another brand will suffice. Allison has done extensive testing with other synthetic fluids and has published a TES 295 specification to identify which brands are compatible with Allison transmissions. Any ATF that is approved by Allison will qualify for the extended service intervals identified in Allison service schedules.
| Gear Lube Chart Click to enlarge |
 |
Gear Lubes
Gear lubricants are used for high-load areas that receive friction during motion, such as rear axles and wheel bearings. Gear lube is heavier than motor oil and ranges between SAE 75 and SAE 140 in viscosity. Gear lube does not have to deal with the combustion requirements of an engine, so its main concern is to provide lubrication to equipment under high operating temperatures and loads.
Gear lube applications generally fall into one of two categories — standard duty or extreme duty. Most situations require basic 80W-90 gear lube, used for wheel bearings, gear cases, and rear axle ring and pinion gear sets. In some automotive applications, limited-slip differentials are used. This adds a bit of complexity to the lubricant requirement, because the limited-slip differential utilizes clutch plates to tie both wheels together for improved traction, yet still allows them to slip when turning corners.
In some cases, the gear lube requires an additive, or a special gear lube that is designed to work in limited-slip applications must be used. If your motorhome has a limited-slip differential, be sure to check the owners manual to determine what is required. Gear lube that is designed for limited-slip applications also can be used in standard open differentials without any problems.
Sometimes conditions are extreme and the manufacturer has determined that greater protection is required. In those instances, a heavier gear lube, such as SAE 140, will be specified. Actually, this is the perfect place for a synthetic gear lube. Many synthetic gear lubes come with an SAE 75W-140 viscosity rating. This multiviscosity gear lube flows well in low temperatures with its 75W rating, yet it has the rating of an SAE 140 gear lube when things get hot. A synthetic 75W-140 gear lube is the ultimate protection for any axle or gearbox, such as a cooling fan jackshaft. Synthetics are also less prone to foaming than conventional gear lubes, which allows for more efficient lubrication.
Hydraulic Oil
Hydraulic oil is commonly used in diesel pushers to operate power steering units and any hydraulic fan motors. If your motorhome has a side radiator, it also may have a hydraulic motor driving the fan. This motor, as well as the power steering system, is driven via a hydraulic pump that is coupled to the engine and fed by a hydraulic fluid reservoir. Hydraulic oil doesn’t have to deal with combustion byproducts, but it needs to be clean and nonfoaming to provide adequate protection to the components in the hydraulic system and also to transfer power from the pump to the motor.
Hydraulic fluid generally is used in either AW32 or AW46 formulas. The “AW” abbreviation stands for antiwear, and it is strictly used to identify hydraulic fluids. The numbers 32 or 46 represent the weight of the fluid, with higher numbers indicating a heavier fluid. AW46 is the type most frequently used in motorhome applications. Keeping this fluid cool and free from moisture or dirt is critical, so filter changes and fluid changes are part of a routine service schedule.
Chassis Grease
You might think that all grease is the same, but there’s actually quite a bit of difference between the various formulations and their applications. Not every component has the same lubrication requirements, so the ideal grease won’t be the same in every situation either. Matching the correct grease to the application will increase the longevity of those components.
Classification of grease is much easier than motor oils. Whereas motor oil is rated in SAE numbers, the viscosity of grease is referred to by its NLGI (National Lubricating Grease Institute) rating. The most popular chassis grease is an NLGI 2, which is widely available. An NLGI 1 rating would be a thinner grease that melts and flows at a lower temperature and is probably the stuff you’d want in your equipment if working the Alaska pipeline, but NLGI 2 works for 90 percent of automotive applications. Conversely, NLGI 3 grease is stiff and designed to be used in extreme heat conditions; therefore, it has no real application in the RV industry.
Most greases are lithium-based, although synthetic greases that offer increased protection levels are available. In most applications, synthetic grease won’t offer enough benefits to offset its additional cost and is better suited for extreme-duty conditions.
Not all lithium greases are identical, because there’s more to grease than lithium, which is just the base upon which the grease is formulated. Plain lithium grease works well for wheel bearings but is marginal for driveshaft universal joints and front-end components. The latter rely on a thin layer of grease to separate two metal surfaces so they don’t gall and bind. If enough force is applied to these two surfaces, the grease can compress and slide away, allowing metal-to-metal contact and increased wear. In addition, when surfaces pull apart from each other, the grease film can fall away rather than stick to the surfaces. Fortunately, more advanced greases improve upon the basic lithium grease. These are still lithium greases, but they’ve been enhanced with additives to improve the characteristics of the grease. Naturally, they cost a bit more than entry-level lithium grease but are well worth it.
One of these characteristics improves the tackiness of the grease. If you place a small wad of lithium grease between your thumb and index finger and squeeze, much of the grease will ooze out, but a small layer will remain. When you pull your two fingers apart, however, you’ll see that the grease breaks free and leaves a slight film on your fingertips. Each time you squeeze and release, you’ll lose more of the lubricant, and eventually there won’t be any left. Better-quality greases are available to improve the tackiness of basic lithium grease. If you were to place some of this better-quality product between your fingers and do the same test, you’d find that the grease would tend to stick to your fingertips and it would be harder to pull them apart. When you did pull your fingers apart, if you looked carefully, you’d notice that the grease would stretch like strings between your fingertips. This “tacky” version of the grease will do a better job than less-expensive lithium grease by staying in place more effectively.
When two surfaces are being forced together, which is typical of a ball joint or tie-rod end, the grease tends to squish out from between the two surfaces. Finding a lubricant to keep these two surfaces from coming into contact with each other is a huge benefit to component longevity. Moly grease meets this need. Molybdenum is technically a metal, but moly particles are actually lubricants and won’t scratch or damage metal surfaces. When moly is added to grease, it comes in the form of small, round particles that act as miniature ball bearings. Moly’s unique characteristic is that it will not scratch the metal, yet it is very hard and won’t crush or be destroyed when put under pressure as two surfaces are trying to squeeze the life out of the moly particles. The moly particles are carried in the grease to prevent metal-to-metal contact and allow the grease to filter in and around the small moly particles to cool and lubricate the components.
Moly grease typically is black in color and is messy to clean up, but it’s an excellent choice for front-end components and universal joints. One application where moly grease is not recommended is for wheel bearings. The moly particles tend to force the rollers away from the races, which tightens the bearing clearance and increases heat. For wheel bearings, it’s best to go with a fibrous general-purpose or tacky grease that has no moly in it.
There are super greases available. Synthetic grease is available from many lubricant suppliers. Synthetics offer a greater temperature range than conventional greases and are great for extreme conditions, but the vast majority of RV owners won’t realize the benefits of them, because they don’t encounter those extremes.
My personal favorite is a lithium-based grease with a tacky property that also contains moly, such as Schaeffer Oil #221 Moly Ultra, Kendall’s L-428 Tough Tac, Mobil Centaur Moly, or Valvoline Palladium. These greases offer excellent tackiness, as well as moly particles. They resist water penetration, hold up well to heat, stay in place, and resist shock loads. I’ve been running this type of grease for a long time in numerous vehicles, and my universal joint and front-end component longevity is remarkable.
One area in which you don’t want to use a good grease is on the slack adjusters, which are used on air brakes and are designed to self-adjust as you apply them. In order for the self-adjusting feature to work properly, some friction is necessary. If you use a good moly grease, the adjusters will be too slippery and won’t self-adjust. Your best bet is to buy a tube of inexpensive grease and keep that loaded in a second grease gun that is used strictly for lubricating the slack adjusters.
Keeping It On The Road
A proper maintenance cycle for your motorhome revolves around matching every component with the correct lubricant. The owners manual provided by the manufacturer will detail the minimum specifications required, but keep in mind that exceeding those specs with a higher-quality lubricant generally will yield greater longevity. Always follow the recommended service schedule for the vehicle, and keep your components clean and the filters changed. Taking proper care of your motorhome will save you money over time and allow you to continue to enjoy your travels.