KEEP IT COOL
BY JEFF ROSENFELD
You`re pumping the attack engine at a house fire. It is a hot summer day, and you begin to smell a strange odor. After looking around the piece for the source, you notice steam blowing out from the engine covers. The engine water temperature gauge is pegged at 240°F. You think, “Sure hope the chief doesn`t blow like this when he finds out the engine has overheated.”
Overheating a diesel engine can have disastrous results. Even a minor run of high-temperature operations can lead to warped or cracked cylinder heads and blown head gaskets. Unit downtime and expense are debilitating for any department.
Diesel engines are designed to operate within a specific temperature range–usually 160°F to 185°F for natural aspirated engines, and up to 195°F for turbo-equipped models. Newer units with electronic controls can actually reduce the power output of the engine by throttling it down (NFPA 1901 prohibits shutting down the engine completely). This shutdown can occur at 205°F on some models. Imagine pumping on the fireground and having the engine slowing to idle with crews inside!
The cooling system is comprised of a radiator, a belt-driven fan, a water pump, a set amount of circulating coolant (water/ antifreeze solution), hoses, and two heat exchangers on the side of the engine block. Also needed is an uninterrupted flow of fresh air. The basic concept of a cooling system is that the coolant is circulated through the engine by the water pump, absorbing the heat and carrying it to the radiator where the moving air removes the heat from the coolant to the atmosphere.
ADDITIONAL HEAT LOADS
In heavy fire apparatus, however, additional heat loads must be dissipated. Two separate water-cooled heat exchangers that cool the engine oil and the automatic transmission fluid are attached to the side of the engine block.
A feature unique to fire apparatus is the midship engine with the radiator located behind the driver in the jump-seat area. With the radiator in this area, fresh air must be channeled through vents on the side of the cab and from underneath the truck. The heated air is then blown over the engine and forced under the rear area of the truck. While this was not a problem years ago, modern trucks have larger engines and increased pumping capacity that have added tremendous heat loads that must be dissipated.
Other advances in modern apparatus include turbochargers, high-amp alternators, and air-conditioning, all of which transfer heat to the cooling system. To combat air-flow problems, some manufacturers have moved the radiator air intake to the front of the cab. The air flows through a straight tunnel to the radiator.
Why does overheating usually occur during pumping and not while driving? When driving, air is forced through the engine compartment by the truck`s movement. But when stationary, the engine fan must pull all the cooling air through the radiator and push the hot air over and away from the engine. When pumping, the engine can be using most of its rated horsepower. The cooling requirement is substantial when the coolant also must cool the engine oil and the automatic transmission fluid. The automatic transmission is locked in high gear and is also under tremendous and continuous load. While the driver operator cannot control the elements of physical design of the apparatus, you can take steps to work around them to prevent overheating.
PRECAUTIONS AGAINST OVERHEATING
When inspecting the apparatus, check to see that the coolant is at the proper level and look for debris such as leaves or plastic bags that may be blocking air flow to or away from the radiator. Also check to ensure that all fan belts are in place and properly tensioned. During monthly maintenance, wash road grime away from the radiator with an environmentally friendly degreaser and water stream. This cleaning alone can reduce operating temperatures 10°F.
When you start pumping on a hot day, anticipate that overheating may creep up on you. To prevent being caught by surprise, take the following measures ahead of time:
Start by turning off the air conditioner, if the apparatus is so equipped. The attack pumper`s crew area probably will not be used for rehab.
Turn off any unneeded electrical loads. Full warning lights are not needed if you are parked on a dead-end street or in a driveway.
Ventilate the engine compartment by opening the engine covers. Opening this area will add to the noise level around the truck, but the fan will be able to push the hot air up and away instead of trying to force it under the apparatus. If you have enclosed jump seats, block open the jump-seat doors and open the engine covers–anything to give the hot air a place to escape from the engine. When you open the engine covers, remember to set up a safety area in the jump seats so no one gets injured by the rotating fan or belts.
Open the auxiliary cooler to help remove heat from the coolant and expel the heat into the pump`s discharge water.
As a pump operator, match pump pressures to fire conditions. High pump pressures are not needed for overhaul procedures. Reducing discharge pressures reduces the load on the pump, transmission, and engine.
As is always the case on the fireground, unexpected problems do occur. If you have done all you can to prevent overheating and you notice the temperature gauge creeping up anyway, try to get another pumper to take over your assignment. If this is not possible, try setting up a smoke ejector to blow fresh air toward the radiator. Another option is to spray a fog pattern from a booster line onto the radiator, taking great care to see that water does not enter the engine`s air intake.
Radiator refill valves, present on some apparatus, should be used only as a last resort. The radiator and cooling system work at about 15 psi. If you were pumping at a 130-psi pump pressure, this full amount could be sent to the radiator if the valve is opened too far, causing the radiator or other components to burst. If you must use this valve, open it only a crack. Do not remove the radiator cap. The system is extremely hot, and opening the cap may discharge large amounts of steam and water. When you see a small stream of water discharging from the radiator overflow line, shut off the valve.
Preventive maintenance and anticipation of problems are key to preventing unexpected breakdowns. n
THE CAB HEATER AS A HEAT EXCHANGER
Apparatus also are equipped with an additional heat exchanger that is often overlooked in summer: the cab heater.
If the engine begins to run hot, the following steps should be taken:
Set the temperature control on high.
Open the defroster vents.
Put heater and defroster fans on high.
Turn on crew cab heaters, if so equipped.
Open all cab doors.
JEFF ROSENFELD, a driver pump operator assigned to Engine Company 16 of the Virginia Beach (VA) Fire Department, joined the department in 1976 as a volunteer and became a full-time paid firefighter in 1979. He is a certified Fire Officer 2, Fire Instructor 3, driver pump operator, and aerial operator instructor; a National Registered EMT; and an adjunct instructor at the National Fire Academy.
