Is your motorhome’s circulatory system in good health?
By Peter D. Du Pre
Most people understand the importance of checking and changing the oil in their motorhome as part of the vehicle’s regular maintenance schedule. Insufficient or degraded oil can lead to poor engine performance and engine damage. The same is true for a vehicle’s cooling system, but it doesn’t seem to get equal attention. An engine that’s allowed to run hot over an extended period of time can suffer the same type of internal damage brought on by insufficient lubrication. So, it’s just as important to consider the health of your cooling system as you develop your maintenance schedule.
Many motorhome owners have the misconception that overheating problems occur only in the summer. That is not true, according to Nick Gulli, marketing manager of replacement products for Goodyear’s Engineered Products business. Overheating problems can occur at any time of the year regardless of the weather.
“Overheating caused by a faulty drive belt or a broken radiator hose can give RVers problems in the fall and winter, too, although it is summertime [when owners encounter] the most problems,” Mr. Gulli said.
Summer is when most motorhomes are on the road and when ambient temperatures are highest. Combine this with the fact that many motorhomes spend a good portion of fall, winter, and spring parked in a storage facility, allowing time for belts and hoses to dry out, and it is easy to understand why so many cooling system failures happen soon after the travel season starts.
Unfortunately, in a motorhome, overheating caused by a broken drive belt, burst hose, or malfunctioning thermostat can be very problematic, because the breakdown could occur on a busy freeway, mountain road, or other highway where pull-off room is limited.
“Almost nine out of 10 radiator hose and fan belt failures in RVs create an emergency situation,” Mr. Gulli continued. “They frequently happen far enough away from home that they increase both the cost and inconvenience of repairs, as well as ruin a family vacation.”
Drive belts, fan belts, and hoses are vital parts of your motorhome’s cooling system. Belts deliver power from the vehicle’s engine to other vehicle components, such as the alternator, air-conditioner compressor, radiator fan (on older vehicles), and other items. A broken drive belt can cause overheating and allow the battery to completely discharge, leaving you stranded.
Hoses are just as important. They transport thousands of gallons of hot, pressurized coolant to and from the radiator every hour, and also serve as shock absorbers between the engine and the cooling system connections, protecting them from possible damage.
Engine compartment temperatures during hot summer weather can reach as high as 280 degrees Fahrenheit. Heat breaks down coolant, hoses, and belts and puts additional strain on the water pump. As the system ages, the belts can fray and develop cracks, while hoses deteriorate both from the inside and the outside. Sludge starts to build up in the coolant, eventually clogging the internal passages of the radiator and engine. After a while, any additional stress caused by low-speed, high-rpm driving, such as when towing a trailer or driving up mountain roads, can cause the engine to overheat.
To avoid these problems, you should have the cooling system inspected before you head out on the highway at the beginning of the travel season. Take your motorhome to a qualified service center and have them inspect the entire heating and cooling system, not just the drive belt(s). Have the shop test the coolant for acidity and its ability to withstand low temperatures without freezing, as well as test the pressure relief ability of the radiator cap, look at the integrity of the overflow tank, inspect the belts for wear, and check the hoses and hose clamps for tight seals.
Belts And Hoses
When inspecting your motorhome’s cooling system, check the belts and hoses first, as problems with these components are the primary causes of overheating. Just make sure the engine is turned off, the vehicle is in park, and the emergency brake is set before you start. Examine the hoses for cracks, bulges, splits, hardness, or sponginess. Replace any that look damaged or disfigured, or are mushy, overly soft, or rock hard. Not sure whether a hose is okay? Simply squeeze it between your thumb and forefinger. The hose should feel firm and yet still be pliant. If the hose feels mushy or too soft or if it’s rock hard and cannot be squeezed, it should be replaced.
Drive belts (fan belts or V-belts on older units) generally last longer than hoses, but they don’t last forever. Most maintenance schedules suggest replacing these parts between 40,000 and 60,000 miles. But on the average motorhome, it may take eight years to reach 40,000 miles. That’s why most RV technicians suggest replacing the belts every other year, especially since many of the new composite drive belts don’t exhibit any signs of fatigue until they fail, and because most motorhomes spend the majority of the time parked. During these prolonged periods of inactivity, drive belts can dry out and become brittle, failing soon after the summer travel season starts. When inspecting the belts, you won’t be able to tell whether they are in good condition by looking at the part that faces out. So, grab the belt with your fingers and twist it to show the underside. Look for glazed sidewalls, cracks, fraying, or missing chunks. Check for missing or cracking ribs on ribbed drive belts.
It is also a good idea to have the belt tension checked. Improper belt tension is a primary cause of belt failure. If the belt is too loose, it won’t drive the alternator or water pump and will wear prematurely. A belt that is too tight tends to crack on the underside and can put additional strain on the alternator and water pump.
One problem that can occur with serpentine-design drive belts is premature wear caused by misalignment of the belt tensioner. This is brought about by excessive wear of the bearing shaft on flat spring tensioners. The tensioner cannot be adjusted or repaired. So, if you notice that the edges of the drive belt appear to be wearing or fraying, have your service technician adjust the belt alignment and also check the flat spring tensioner. If the bearing shaft is worn, the tensioner will need to be replaced.
A properly adjusted fan belt (in older, puller-type RVs) should flex about 3/4-inch when pressed in between the pulleys with the thumb. Adjustment usually is done by loosening the alternator mounting bolt and moving the alternator slightly in the appropriate direction. Serpentine and ribbed drive belts used on newer motorhomes may not flex this much when properly adjusted. To check and adjust belt tension, a tensioning gauge is needed to measure the flex. Unless you have the tool, let a technician do the job.
Coolant is usually a 50-50 mixture of ethylene glycol or propylene glycol and water. The percentage can vary between 40 and 60 percent coolant mixed with the appropriate amount of water, depending upon the engine and the environment. Most large motorhomes use propylene glycol, while many Type B and Type C units use ethylene glycol. In addition, the coolant includes corrosion inhibitors, water pump lubricant, and antiscale inhibitors as a part of its makeup. The coolant’s job is to lower the freezing point and raise the boiling point of the water portion of the mixture. This makes it possible for heat generated by the engine to be absorbed and transferred to the radiator, so the engine can operate under a wide variety of environmental and load conditions. Coolant typically does a good job, but it breaks down with age, picking up contaminants from within the system that cause sludge. The coolant also becomes acidic, which is why it should be checked regularly for acidity and completely changed out on a regular schedule.
When having your cooling system inspected, have the technician check the condition of the coolant, radiator, and heater core. I don’t advise doing this yourself, because coolant, especially those formulated with ethylene glycol, is an environmentally hazardous substance. It pollutes the water table and is poisonous to people and animals. Your technician has special tools and procedures for changing coolant. In any case, when the coolant is replaced, have the technician backflush the system to remove scale, corrosion, and mineral deposits that build up over time and rob the system of efficiency. Some coolants need to be changed more often than others, so check the recommendations for your vehicle and the type of coolant that you are using. Depending upon operating conditions, more frequent coolant changes may be necessary.
Realize also that the chemical makeup of coolants used in newer motorhomes may differ from the traditional green ethylene glycol we all grew up with. Consequently, some coolants may be yellow, red, pink, or orange. These are designed for use in specific types of engines and may have recommended change-out frequencies that differ from the traditional two-years/15,000 miles. So, be sure to follow the recommended guidelines for cooling system maintenance that come with your motorhome.
For winterizing and long-term storage, an RV/marine antifreeze is recommended. RV antifreeze is made of propylene glycol and is intended to protect both the engine and the drinking water system and plumbing from winter freezing. This type of antifreeze contains a nontoxic corrosion inhibitor such as dipotassium phosphate, but since it is intended to be flushed out seasonally, the corrosion inhibitors are not designed to provide long-term protection.
On some larger diesel pushers, it may be necessary to add a supplemental cooling additive (SCA) to the antifreeze. Heavy-duty diesel engines require the addition of an SCA to protect the cylinder liners. In automotive use, antifreeze has a high level of silicates to do this job. In diesels, however, the silicate levels are lower. A universal-grade coolant designed for both automotive and heavy-duty use balances the silicates so that they are sufficient for both needs. Even so, certain heavy-duty diesel applications will require the use of SCAs because of the way some diesel engines are designed.
For improved heat transfer, many heavy-duty engines have wet sleeve liners that vibrate during operation. This vibration creates air bubbles that implode against the liners’ outer surface, or cavitate, which causes pitting that can damage or destroy the wet sleeve liner. Because of this problem, heavy-duty coolants must contain a special nitrite inhibitor, extra defoamer, scale inhibitor, and buffers that come in the form of an SCA added to the coolant.
Consequently, a proper maintenance schedule for adding SCAs is as important as adding the correct amount of initial supplemental additive to begin with, because over time the inhibitors deplete. Most experts recommend adding an SCA at least every 200 service hours or 15,000 miles (consult the engine manufacturer for exact recommendations). While this is a rough guideline, the only way to really know whether your vehicle needs additional SCA is with three-way test strips that check the coolant for SCA, freeze point, and pH. Testing for SCA should be done every six months. Too much SCA in the coolant is just as bad as too little. A trained technician should have no trouble determining whether your vehicle needs more SCA.
It is also wise to make sure that the coolant filter is cleaned or changed (depending on the vehicle) whenever the coolant is replaced, if your vehicle is so equipped. As previously mentioned, over time the coolant can develop sludge and scale, which reduces its ability to transfer heat away from the engine. The filter traps these impurities, which aids efficiency and prolongs the life of the coolant. Just as you change the oil filter with every oil change, make sure to change/clean the coolant filter with every coolant change, or more often if the maintenance schedule demands it.
Many diesel engines include filters that also contain SCAs. The filter can contain from zero units to 16 units of SCA. Filter replacement should be part of routine maintenance to help maintain the SCA level, and the filter should be replaced whenever the coolant is changed.
One way to keep temperatures down and help prolong the life of the coolant is to make sure that the radiator cooling fins are clean and free of debris, dirt, bugs, and so on. The clearances between the cooling fins on a radiator are extremely narrow, so anything that blocks airflow will contribute to higher operating temperatures and possibly cause the engine to overheat. Generally, spraying the radiator with a high-pressure wand will clear any dirt or debris blocking the cooling fins. (Do not use a pressure-washer on its hardest setting, as intense spray can bend the fins.) If a spray-off is not practical, use a whisk broom to gently brush away dirt and debris. Keeping the radiator cooling fins clean can make the difference between overheating and running at optimal temperature in warm weather. Also, in areas known for dust or heavy bug infestations, a daily check of the radiator fins is a good idea.
Rear-engine diesel motorhomes have the radiator at the back of the motorhome, and dirt typically is not deposited on the radiator but rather on the front of the charge air cooler. This equipment can be cleaned only from the front (access from a bedroom or closet floorboard). Cleaning the charge air cooler should be done annually.
Often, and especially with motorhomes that spend a lot of time in storage, coolant loss can occur even if the hoses and clamps appear to be in good condition. These leaks usually are caused by a loss of coolant system integrity at the point where the hose and the hose connection pipe meet. Most of the time these leaks are what’s known as “cold leaks,” and they happen when the engine/cooling system is cooling or cold. The problem is caused by the fact that hose connector pipes, rubber (or silicone) hoses, and hose clamps all expand and contract at different rates. When this happens, some coolant will leak out, but the leak generally stops when the system is brought up to operating temperature and the components expand, sealing the leak.
Cold leaks are often more noticeable when silicone hoses are used, since these don’t adhere to the hose connection pipes the way rubber hoses do. This is not a significant problem in the RV world, but it is a problem in heavy-duty commercial applications. Some large diesel engines used in motorhomes are equipped with silicone hoses instead of rubber, so a forewarning here is important. Another issue with units equipped with silicone hoses is that the material permeates water at a rate that is 10 to 15 times higher than other hose materials. When this happens and coolant loss occurs, many technicians and RV owners top the coolant level with straight coolant or even the “proper” 50-50 mix of coolant and water. However, the silicone hoses permeate only water, not the coolant part of the mixture, meaning that the incorrect mix of coolant will be present in the cooling system, which can affect the efficiency of heat transference. So, if your diesel pusher is equipped with silicone hoses, make sure to have the coolant tested for mixture strength, as well as acidity, when you top off the system.
Although the hoses typically fit snugly over the hose connection pipes to create a tight seal, hose clamps are needed to maintain system integrity; to keep the hoses from working loose as the engine vibrates; and to maintain a tight seal when internal pressure mounts as the hot coolant circulates. Currently, there are multiple hose clamp designs on the market, and different types of clamps are used by various engine manufacturers. In addition to the aforementioned, the clamp provides a uniform tension and seal around the hose end where it fits over the connection pipe. The clamp also needs to have overtightening protection; to distribute tension evenly so that no cold leaks result; and to be able to withstand the tough environs of the engine compartment, where high heat, oil, rainwater, and leaking coolant can contribute to degradation of the clamp. For this reason, many clamps are made of stainless steel. The most common stainless-steel clamp features a worm screw design, commonly sold in auto parts stores. While the stainless-steel clamp holds up well to engine compartment extremes, it may not be the best to use on the hoses on your system, which is why so many different clamps are available. The specific clamp needed is determined by the type of hose pipe connection, the type of hose being used, and even the thickness of the hose, as well as the maximum operating temperature of the engine. Use the wrong clamp and you can damage the hose connection pipe, or even weaken the hose by cutting into it.
A new type of clamp that eliminates these problems is the polymeric clamp, which is made from a thermoplastic polymeric material. This “clamp” is actually a high-tech plastic ring that fits over the hose and hose pipe connection. Once the polymeric clamp has been installed, a heat gun is used to “tighten” or shrink it around the hose and hose connection pipe for a leak-free seal. Furthermore, the clamp will seal over any shape hose and even seal out-of-round connector pipes. While this type of clamp also expands and contracts, it maintains a leak-free seal when the engine is cold and it essentially reforms to the hose shape every time the engine is brought back up to operating temperature.
Thermostat And Temperature Sensor
Two other components that are very important parts of the cooling system are the thermostat and temperature sensor. The thermostat is the device that controls the operating temperature of the engine by opening and closing the lines to the radiator to maintain a constant temperature. It is usually located in a housing on the head of the engine. Although tests can be done to determine whether a thermostat is properly functioning, the best way to check it is to simply inspect the cooling system for leaks and then keep an eye on the coolant temperature gauge on the dash. If you are sure that the system is holding integrity and that all operating parameters are constant, a wildly fluctuating temperature gauge could indicate that the thermostat is faulty. But it also could signal that the temperature sensor has gone bad. If you are getting extremely high or low temperature readings, check the temperature sensor first, and if it checks out okay, then it’s likely the thermostat is at fault.
The water pump is the heart of the cooling system and is responsible for moving thousands of gallons of hot coolant through the system every hour. The pump is located at the front of the engine and is driven by the serpentine belt (V-belt on older units). It is a maintenance-free unit that should last for years and years, and tens of thousands of miles, provided you run the proper percentage mix of coolant and water. Although a water pump can fail without warning, there generally are indications that the system is beginning to fail long before it actually does. One such clue, of course, is a consistently higher operating temperature, even on flat roads and with no load placed on the unit. The elevated temperature is caused by the pump’s inability to move the proper amount of coolant mixture through the engine and radiator. Another clue to water pump failure is bearing noise. This can be difficult to hear, especially in a diesel pusher where the engine is located in the rear of the motorhome. Often, the noise is heard only from outside the unit while the vehicle is at idle. Either way, a failing water pump is not a repair job that can be put off. If the pump fails while you are on the road and driving in hot weather, not only will it ruin your trip, but the failure of the pump could severely damage the engine. So, if you suspect that the pump is beginning to fail, have it checked out by your RV service center and replaced if necessary.
As you develop your motorhome’s maintenance schedule for the upcoming year, make sure it includes a cooling system checkup to assure that your engine will run at the optimal temperature throughout the travel season.