Tips for making sure that your motorhome’s engine keeps its cool as the hot summer months approach.
By Peter D. duPre
Nothing ruins a summer vacation quicker than an overheating engine. There you are behind the wheel of your weekend getaway when a quick glance at the instrument cluster shows a temperature gauge needle creeping upward. The next thing you know, a little red light comes on, the engine loses power, you are stuck on the side of a highway, and your holiday weekend goes up in the air along with the billowing cloud of steam emanating from the engine compartment.
Overheating engines are a common problem for all motorists and are one of the most frequent causes of summertime breakdowns, but they are particularly troublesome for motorhomers. High hills, low rpm operation, heavy loads, and hot weather all combine to put added stress on your engine’s cooling system. All too often, the overheated motorhome is precariously parked on the side of a steep grade with a portion of the coach sticking out into the traffic lane. Anyone who has ever driven the Grapevine or Baker grades in California or crested the Rockies in Colorado in their RV knows all too well what I am talking about. Even if you haven’t actually experienced an overheating breakdown, odds are you’ve passed numerous coaches that didn’t make the grade and were stranded along the roadside. And as we all know, having a motorhome towed costs a lot more than towing a Toyota Corolla.
Engine compartment temperatures during hot summer weather can be as high as 280 degrees Fahrenheit, and coolant temperatures frequently rise above 240 degrees Fahrenheit. Heat from inside and outside the cooling system breaks down coolant, hoses, and belts, and puts an additional strain on the water pump. As the system ages, drive belts fray and develop cracks, while the hoses deteriorate from both the inside and the outside. Sludge starts to build up in the coolant, eventually clogging the internal passages of the radiator and engine. After awhile, any additional stress caused by low-speed, high-rpm driving “” such as towing a vehicle or driving up mountains “” can cause overheating. Then you are not only stranded alongside the highway with a broken drive belt or burst radiator hose, but you also may have incurred serious engine damage.
According to Nick Gulli, marketing manager, replacement products for Goodyear’s Engineered Products business, “Almost nine out of 10 radiator hose and fan belt failures create an emergency situation … that can lead to major engine problems.” Caterpillar engineers agree and point out that 40 percent of diesel engine failures are caused or aggravated by cooling system problems.
To avoid a breakdown and serious engine damage, both Goodyear and Caterpillar engineers suggest having the cooling system inspected before the summer season. Take the vehicle to a qualified service center and have the technicians inspect the entire heating and cooling systems, not just the belts. They will test the coolant for acidity and its ability to withstand low temperatures without freezing, 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. If problems are discovered, don’t settle for a temporary repair job. Odds are that if a bad hose or belt is discovered, the rest of the cooling system is probably right on the edge of failure; you’ll need a major cooling system service, which includes flushing out the system, changing the coolant filter (diesels), replacing the coolant, installing new belts and hoses, and possibly changing out the thermostat.
How cooling systems work
An engine’s cooling system consists of a radiator, a radiator cap, a water pump, hoses, a temperature sensor, a temperature gauge, fan(s), a heater, a thermostat, internal engine cooling passages, a coolant filter (diesels), and the coolant (mixture of water and antifreeze solution). When the engine is started, the cooling system brings the engine up to its operating temperature as quickly as possible, limiting the flow of cold coolant through the engine by use of a thermostat.
When the engine is started, the thermostat is closed and a reduced amount of coolant is allowed to circulate. Once the coolant in the engine warms up to a particular temperature (165 to 210 degrees Fahrenheit), the thermostat opens, letting the coolant circulate through the radiator so it can cool down. As the engine continues to run, the excess heat from the block and cylinder heads is transferred to the coolant, which transfers the heat out as the coolant passes through the radiator. Depending upon conditions, the thermostat controls coolant circulation throughout the operating cycle to keep temperatures constant. Except in the coldest of climates, the thermostat and radiator alone are not enough to moderate temperature, so a temperature sensor is used to activate an electric or clutch-driven fan that forces more air to pass through the radiator, thereby reducing coolant temperatures more quickly and keeping the engine operating in the most efficient temperature range, no matter the operating conditions.
Because internal-combustion engines produce a considerable amount of heat, the efficiency of the cooling system is vital; this is why motorhomes and big trucks have huge-capacity radiators, heavy-duty water pumps, and possibly more than one fan. Engine manufacturers have designed modern gasoline and diesel engines to run at high internal operating temperatures in order to reduce emissions and improve fuel economy. To reach these goals, today’s engines run right on the edge of overheating with in-cylinder temperatures nearing the 2,000-degree-Fahrenheit mark.
When the fuel is ignited in the combustion chamber, approximately one-third of the energy in that fuel is converted to kinetic energy for moving the vehicle. (This is what pushes the pistons down.) Another third of the energy is expelled from the combustion chamber as hot exhaust gases through the tailpipe, and the remaining third of this energy (heat) is transferred to the coolant (and is reduced as the coolant passes through the radiator).
Without the transfer of excess heat to the coolant, internal engine parts would begin to absorb heat and expand. Pistons would seize and some internal parts would start to melt. That’s why an efficient cooling system is so important. To transfer the heat out of the engine, the water pump needs to move hundreds of gallons of near-boiling liquid coolant through the system every hour.
An often unsung part of the cooling system is the heater. While we use the in-dash heater to warm up the driver’s compartment on cold mornings and to defrost the windshield, few of us think of the heater as an important part of the cooling system. The fact is, however, that under marginal operating conditions, turning on the heater will usually keep temperatures in the safe zone. Your engine’s heater core is nothing more than a smaller, secondary radiator. When the heater is turned on, a gate valve is opened that allows hot engine coolant to circulate through this smaller radiator where it passes the heat into the driver’s compartment. If you notice engine temperatures rising too quickly, turning on the heater will often keep the engine from overheating, provided you haven’t blown a hose or a drive belt. You may have to open the windows to help keep cabin temperatures tolerable, but being a little warm is always better than being stranded.
Doing your own system checks
Although having your cooling system checked annually by an RV professional is important, it doesn’t mean you can ignore the system the rest of the year. Make it a practice to regularly examine the cooling system components before every trip, looking for obvious problems “” even if you just recently had the system serviced. Because of the nature of RVing, motorhome cooling systems are more prone to problems.
Most motorhomes spend much of the time in storage, but when they are used, it is often for extended periods, so problems develop. When the engine is operating, ambient engine compartment heat attacks hoses and belts from the outside while hot coolant slowly breaks down hoses on the inside. When the vehicle is parked for extended periods, the belts and hoses may dry out and become brittle. Even the coolant isn’t immune from decay; it picks up acids and sludge and, over time, loses some or all of its ability to slough off heat efficiently.
As I said earlier, according to the engineers at Goodyear Tire & Rubber, hose and belt failures are the primary causes of overheating problems, so it makes sense to keep a close eye on them. To check the hoses yourself, put the vehicle into “park,” set the parking brake, make sure the engine is off, and open the engine compartment access. Take a close look at the radiator and heating hoses, looking for obvious problems such as leaks, cracks, splits, and bulges. Then, using your thumb and forefinger, give each hose a squeeze. (On longer heating hoses, check them in two or three different areas.) They should feel firm but pliant. If the feel is mushy, brittle, or stiff, they need to be replaced. Be sure to carefully inspect the hose clamps, too, and replace any clamps that are rusted, sprung, or distorted. Plan on replacing all hoses and clamps every two or three years, even if they appear to be okay.
Drive and/or fan belts operate the power steering pump, engine air-conditioning compressor, water pump, and alternator. They generally last longer than hoses, but they won’t last forever. Industry experts suggest replacing all drive belts every 40,000 miles or two years (whichever comes first) regardless of their appearance and especially if the vehicle has been operated under dusty and/or high heat conditions. The two-year rule for changeover is important, because today’s new-composition drive belts often don’t show any wear at all and the first sign of trouble is usually total failure. The maintenance schedule in your owners manual will give you the specifics for your engine, but when in doubt, follow the above maintenance schedule.
To check a belt’s condition, examine both sides for obvious wear such as chunking, splitting, cracking, or fraying. Any one of these conditions means the belt is near failure and needs immediate replacement. While checking belt condition, it is also a good idea to check for belt tension. Drive belts need a certain amount of tension to drive the pulleys on the various components they pass through. Too much or too little tension is bad. A belt that is too tight puts undue stress on the water pump, alternator, air-conditioning compressor, and power steering pump, causing the bearings to wear prematurely. A belt that is too loose will slip, become glazed, and fail to drive these important engine components, so you could end up with an overheating engine and a dead battery. To check tension, simply push down on the belt with your thumb midway between two pulleys. A properly adjusted belt will generally flex about three-quarters of an inch. Less flex than this means the belt is too tight and more flex means the belt is too loose. Either way, play it safe and have the belt replaced and properly tensioned.
Three basic types of coolant are used in modern engines: the traditional green ethylene glycol (EG); extended-life ethylene glycol, which is usually yellow; and propylene glycol (PG), which is usually red. All are mixed with water before being installed in the cooling system and all break down with age, picking up impurities and becoming diluted so that their effectiveness diminishes over time.
While EG and PG coolants are similar in makeup and do the same job of cooling an engine, they are not generally interchangeable, nor should they be mixed together. For example, PG coolants should not be used in Ford Power Stroke diesels because their chemical makeup can damage aluminum engine parts, certain gasket materials, and even some types of hoses. It is vital, therefore, to consult your owners manual or check with your RV service professional to find out which coolant your engine uses before adding to or changing the coolant in the system.
To assure that it is always in top condition, the coolant should be changed out every two years or 24,000 miles on gasoline engines “” more often if the vehicle is operated under severe conditions. Diesel engines can generally go longer between coolant changes (three years or 30,000 miles), because they have coolant filters as a part of the cooling system to remove impurities. Extended-life coolants can be changed even less often and have a service life of up to 100,000 miles or five years. Check your engine manual or consult the engine manufacturer directly to find out the recommended coolant change interval for your engine.
One of the reasons for recommending a specific mileage/time interval for changing the coolant is that there is no way to tell whether the coolant is at peak efficiency by simply looking at it. You may think that dirty-looking coolant needs changing and while this can be true, it is also true that certain coolant additives can make the regularly translucent coolant look dirty when it is actually in perfect condition. If you want to know the condition of the coolant mixture, you must have it checked for acidity. This can be done either by using a test strip that measures the pH balance of the coolant or by using an antifreeze hydrometer to check the specific gravity of the coolant. Either of these devices can be purchased at auto parts and RV supply stores, but when purchasing a hydrometer, make sure it is compatible with the coolant type (EG or PG) you are using.
For a more accurate reading, a refractometer can be used. This device is by far the most accurate way of checking the coolant temperature protection. It works by magnifying the coolant’s light properties and displaying the results on a temperature scale. The problem with using a refractometer is that its rather high cost ($80 to $200) makes purchasing one impractical for occasional use, so having a professional do this is generally more cost-efficient.
Whether you use an EG- or a PG-based coolant, it will need to be proportionally mixed with water to offer the best temperature and corrosion protection. If the proportion of coolant to water is too low, rust, corrosion, and scale can build up in the cooling system, which can lead to water pump and radiator failure. Rust and corrosion can also erode aluminum engine parts and gasket materials, resulting in costly repair work. If the coolant-to-water proportion is too low, the water in the mixture can freeze when temperatures drop, which can damage the engine.
Too high a concentration of coolant is just as bad. When the concentration of coolant to water is too high, the silicates in the coolant separate out, forming a sludge that plugs heater cores, the radiator, and heater core tubes, as well as the cooling passages within the engine.
The exact proportions of the coolant-to-water mixture depend on the operating conditions and the amount of temperature protection required. Generally, the recommended proportion of coolant and water for most conditions is a 50-50 mix of the two, which will provide temperature protection to approximately minus 34 degrees Fahrenheit. Under severe operating conditions, such as winter in Alaska, the proportions of coolant to water can be as high as a maximum 60 percent coolant and 40 percent water, and under certain operating conditions a mixture of 40 percent coolant to 60 percent water may be acceptable. Check your owners manual for specific recommendations.
A common mistake most people make when mixing coolant with water is to use tap water. Always use either demineralized or distilled water in the cooling system. City or tap water can be used in an emergency, but it is too hard for long-term use, as it contains minerals and chemicals, such as chlorine, that can cause scale and corrosion in the system. Never use soft water in your cooling system; the salts in it can be corrosive to engine parts as well as affect the cooling ability of the coolant mixture.
Diesel engines that use green or EG coolants need supplemental cooling additives (SCA) to protect against erosion that occurs on the outside diameter of the cylinder wall. This erosion, called cavitation, occurs when tiny vapor bubbles form in the cooling system and attach to the outside cylinder wall. The vapor bubbles are caused by the slight rocking motion of the pistons as they move up and down in the cylinders. This rocking motion produces vibrations on the cylinder wall, causing vapor bubbles to form in the cooling jackets on the outside of the wall and creating a low-pressure area. As this happens, more and more bubbles form until the mass of the bubbles causes some of the vapor bubbles to collapse, which, in turn, creates a localized high-stress area on the outside cylinder wall that causes it to erode slightly. Over time this corrosion can make a pinhole in the cylinder wall that allows coolant to enter the combustion chamber and cause severe engine damage. But SCA in the coolant mixture will put a protective coating on the cooling system passages and stop vapor bubbles from building up. Supplemental cooling additives also help to neutralize acid buildup, provide antifoam protection, and reduce scale and general corrosion in the system.
If your coach is powered by a gasoline engine, cavitation generally is not a problem. Diesel engines typically have twice the cylinder pressure of a gasoline engine, and cylinder wall vibrations are more extreme than those in a gasoline engine. So unless your gas-powered RV sees long-term extreme-duty operation, cavitation won’t be a severe problem.
If you experience a coolant spill due to overboiling or while changing out the coolant, be sure to mop it up immediately. If that is not possible, hose it away using plenty of water. All automotive coolants are toxic (especially EG-based coolants), and what’s worse is that they have a sweet smell and taste that makes them attractive to small children and pets. It takes only a small amount of this toxic substance to make a child or pet severely ill, and it can be fatal. Spilled coolant also pollutes ground water, so dispose of it carefully by taking it to a recycling center. You may see PG-based coolant listed as being “nontoxic.” This isn’t true. They are listed that way because in its pure form, propylene glycol is not harmful to humans when ingested in small amounts. In fact, it is often used in food products such as eggnog. However, coolant manufacturers add silicates and toxic chemicals to propylene glycol to make it an effective engine coolant, which makes it harmful to people and animals.
Hire a professional
Although a thorough examination of the cooling system may show that the system looks healthy, you still may be experiencing overheating problems. If you find this is the case, you’ll need to have the cooling system inspected by a professional who can pressure-check the radiator and cap, examine the heater core (an oft-neglected part of the cooling system), test the thermostat and temperature sending unit, and make any needed repairs to the water pump or the fan clutch. By performing regular cooling system examinations and preventive maintenance yourself, you can keep repair costs down as well as avoid a costly and troublesome roadside breakdown.