Why Diesel Engines on Fire Pumps Fail PrematurelyBy Gene Allen,
Allianz Energy, Houston
Allianz Global Corporate & Specialty
Large diesel engines that are used to power fixed fire
protection water pumps appear to have a pattern of premature
failure due to “overheating.” When diesel engines are used in
over-the-road trucks, they normally operate over 6,000 hours before
major repairs are needed. However, many of these engines on fixed
fire protection water pumps are failing with less than 500 hours of
In large flammable and combustible liquids handling complexes,
the total area of process units can be as large as a small town.
Because of the facility size and quantities of flammable liquids,
multiple large (2,500 to 5,000 gpm) fire protection water pumps are
needed. These pumps are almost always powered by diesel engines and
not electric motors because if the facility has a large incident,
such as a Vapor Cloud Explosion (VCE), the electrical supply could
be impaired. Thus, the diesel engine is the driver of choice for
these large fire protection water pumps.
All Photos and drawings by author except as noted
Engine on upper left only had 150 hours of operation before the
top end overhaul / new head
Two ways to cool a water jacketed diesel engine
There are two methods of removing/rejecting heat from water
jacketed internal combustion diesel engines:
1. The method used in trucks and cars is circulation of the
heated water from the engine through a water to air heat exchanger,
called a radiator. Older engine driven firewater pumps, as well as
newer, very large diesel firewater pumps, use radiators for
In cold weather climates, firewater pumps installed outside
would have to be freeze protected.
For current installations, most fire pumps are enclosed in
buildings. If equipped with a radiator, the building can be very
expensive because it would require specially designed ventilation
systems that allow fresh air into the building and hot air exiting
the radiator out of the building. See figure below.
Fig A.11.3.2(b) from NFPA 20, Installation of Stationary Pumps
for Fire Protection, 2013 Edition
Two ways to cool a water jacketed diesel engine (continued)
2. When a diesel engine is used to power something in an
enclosed area, like a boat or other marine application (e.g. engine
room), a liquid to liquid heat exchanger is used to cool the engine
by exchanging the generated internal heat with the cool “sea water”
or “fresh water” from outside the boat. For decades, many diesel
engine drivers on fire pumps could be provided with these liquid to
liquid heat exchangers instead of radiators. These exchanger
equipped engines get raw cooling water from the discharge side of
the fire pump. Traditionally, a “shell and tube” type heat
exchanger is used. See the yellow exchanger mounted in front of the
engine photo below.
The idea of using water to water heat exchangers has been around
in very expensive pleasure boats since the 1920’s. During World War
II, between 1938 and 1945, they were produced by the thousands to
be used in small to medium sized watercraft, landing craft, service
boats, and even fighting craft like the Patrol Torpedo (PT)
All those boats used one or more water to water heat exchangers,
not only to cool the engine, but also to cool the engine intake
combustion air from the supercharger. Additionally, the engine room
was kept cooler by using the outside water to cool the engine
exhaust manifold. The limited space is more than evident when
looking at the photo below of a PT boat and its three giant 12
cylinder Packard engines.
These water to water heat exchangers typically were a standard
shell and tube exchanger with the hot engine water on one side and
the cool raw water on the other. For corrosion resistance, the
choice of metal depended on whether the raw water was “salty” sea
water or “fresh” lake or river water. Also, the exchangers were
bolted together so they could be disassembled for cleaning at
regular intervals. This was done in order to remove foreign
material and scaling accumulation before the exchanger plugged and
the engine overheated.
PT boat Engine Room with three Packard V 12 enginesPhoto with
permission of T. Garth Connelly
The death of the radiator on engine driven fixed firewater
When the economic pressures to reduce costs and expenses came to
the energy industry in the early 1980’s, many energy,
petrochemical, and chemical companies started outsourcing things
like maintenance and engineering. The design of fire protection
water systems slowly became one of the items that was outsourced.
Instead of an in-plant engineer designing fire pumps and systems,
outside vendors took on more and more of the water system projects
including new firewater pump design.
These vendor contractors turned to public standards like the
National Fire Protection Agency’s Code for Stationary Pumps (NFPA
20) for design information. Because NFPA 20 allowed the water to
water exchangers, and fire pump sets with these exchangers are less
expensive to manufacture and install, the contractors influenced
the firewater pump manufacturers to offer more pumps with water to
water exchangers. Industry quickly moved in that direction. Without
the experienced in-plant engineer to be the gate keeper on the
decision, the radiator equipped diesel engine began to
While NFPA 20 provides good information on the design of the
emergency bypass piping, (see above), almost all of the rest of the
raw water cooling loop, including the heat exchanger design, is
left to the discretion of the manufacturer or vendor.
Premature overheating engine failure is from insufficient heat
The “non-mechanical related” premature diesel engine failures
that have been reviewed had one thing in common: they all had water
to water heat exchanger cooling systems.
Why are these water to water heat exchanger equipped engines
1. The raw cooling water flow may be reduced below the minimum
recommended rate before the heat exchanger:
• In some cases, the raw water line is reduced in size at the
supply connection to the source water piping, as can be seen in the
photos to the right. These small connections may have produced
enough cooling flow when the pump was installed, but over time,
these smaller orifices can be restricted by rust or
Raw water Normal and Bypass piping NFPA 20, Installation of
Stationary Pumps for Fire Protection, 2013 Edition
Premature overheating engine failure is from insufficient heat
exchanger cooling (continued)
• The inlet water strainers and/or regulator may be too small
for the larger diesel engines or may be clogged with debris. It is
recommended by some engine manufacturers that the inlet strainers
be disassembled and cleaned before each weekly engine churn test,
not just blown down.
During a recent flow test of a new 3,500 gpm firewater pump,
when the pump was at rated capacity with 150 psi discharge
pressure, the raw cooling water regulated pressure was 35 psi, as
expected. When the discharge was increased to 150% of rated
capacity, the discharge pressure was
97 psi, also as expected. However, the raw cooling water
regulated pressure surprisingly dropped to 26 psi! Closing the
primary supply side valve and opening the emergency bypass side
also resulted in 26 psi. But with both the primary and bypass
valves open the pressure returned to 35 psi.
The strainers were clean, so the strainers and/or the regulators
on this “new installation” unit were simply too small to allow the
correct amount of raw cooling water to flow through the exchanger
at the lower inlet water pressure.
2. Even if the cooling water is flowing at the correct rate, the
diesel engine may still overheat if the heat exchanger loses its
thermal transfer efficiency due to some plugging and/or internal
parts “fouling” (coated with silt or sludge) – see below. Neither
the NFPA nor the manufacturers suggest a schedule for internal
inspection of the heat exchanger.
The raw water going to the heat exchanger is expected to be
“clean”, maybe even potable water. The strainers on the supply line
and even the screen in the regulator (a well-kept secret ) are
designed to remove small particles like sand and gravel. Typically,
the raw water source for fire protection water pumps
(at most of the large flammable/combustible liquids processing
complexes) is from rivers, ponds, or utility water. These are
certainly not potable water sources. These water sources have
materials, silt, mud flakes, small shells, biological growth,
organics, and slime which can slide through the strainers, but
collect in the exchanger due to velocity changes or turbulence. Any
time the fire protection water is supplied by these non-potable
sources, the inspection of the internal parts of any heat exchanger
should be conducted on a regularly scheduled basis.
FM (Factory Mutual) Approval, a third-party certification
organization, has recognized the low flow problem in the raw water
cooling loop by requiring an automatic low flow alarm if the raw
water flow is reduced more than 75% of the required cooling water
requirement. This is a requirement of the FM approval standard for
diesel engine fire pump drivers, section 3.6.1.A May 2012. This
could be a flow sensor, differential pressure sensor, or other
sensor. It should be tested during the weekly and annual test.
Raw water Emergency bypass Per NFPA 20
Why is the engine temperature gauge slow to warn of a pending
The water temperature in the engine is regulated by an internal
“automatic” thermostat. Any diesel or gasoline internal combustion
engine must be warmed before it can perform at peak loading. This
thermostat is closed at temperatures less than 180° Fahrenheit (F)
and then slowly opens to maintain the operating temperature as
close to 180° F as possible.
The thermostat in the engine slowly continues to open as
additional engine cooling is needed if the workload on the engine
is increased. Typically, a thermostat is about half open at 190°F
and fully open at about 200°F. Once the thermostat is wide open and
if there is not enough raw cooling water flow to cool the engine,
the temperature of the engine will quickly rise over the safe
operating limit and result in engine damage, unless manually
stopped within a short period of time.
The engine thermostat will complicate the readings of an engine
temperature gauge, but a well designed raw water system will
provide the necessary cooling capacity to keep the engine
temperature between 180°F and 185°F, even at full engine load while
the pump is flowing at 150% capacity. The closer the temperature is
to the 200°F side or “hot” side of the gauge, the poorer the
exchanger is operating.
Three changes complicating the overheating problem
Diesel powered firewater pumps installed since 2008 could have
three other “things” that will further impede the efficiency of the
raw water cooling system and could very easily contribute to the
diesel driver overheating:
1. Most of these new pump sets have heat exchangers that cannot
be opened for an internal inspection; the heat exchangers,
including the end caps, are welded in construction. Therefore they
are simply replaced when they fail to perform properly . It is
critical to note that a serious obstruction can cause an engine
overheating failure in a matter of minutes.
Today, and for some time prior, almost all fire pumps packaged
with Cummings and John Deere engines, will have these welded heat
exchangers. However, some engine manufacturers still offer engines
that are supplied with a shell and tube heat exchanger that can be
A small welded engine cooling water exchanger on a large diesel
Three changes complicating the overheating problem
2. The raw water going to the engine heat exchanger will
probably be preheated an additional 20° to 25° Fahrenheit. Today,
because the current series of the diesel engines were originally
designed for construction equipment or transport vehicles, they are
being altered to obtain more power and to meet more rigorous
federal emission standards by having better fuel injection system
control and more combustion air.
The better control of the fuel system is accomplished with a
computer controlled fuel metering system, called the Electronic
Control Module (ECM). The ECM has been used on diesel engines in
trucks for years. NFPA 20 has adapted to the change to an ECM by
requiring that each engine be supplied with a second (alternate)
ECM in case the primary system fails. NFPA also correctly states
that both ECM’s should be tested during the weekly fire pump churn
test. Indications are that very few are being properly tested.
The higher flows of combustion air needed is satisfied by
installing a supercharger. To get the maximum power, the hot
compressed combustion air from the compressor side of the
supercharger needs to be as cool as possible to increase the
density. Traditionally, the older, heavy-duty diesel engines had
air “inter-coolers”made inside the air intake manifold of the
engine (inter-cooler or heat exchanger). These inter-coolers used
the low pressure coolant water from inside the engine block to cool
the hot pressurized air before it entered the combustion chamber of
Today, because many of the diesel engines are derivatives of
engines used in everything from pickup trucks to construction
equipment, they all have radiators for engine cooling. They
typically use an external air to air heat exchanger that works like
a radiator to cool the hot compressed combustion air. However, if
there is no engine radiator on the new firewater pump, a radiator
type air after cooler is not likely either. The diesel engine
manufacturers and/or vendors added another water cooled heat
exchanger to cool the combustion air. See illustration below with
thermal images of an actual loaded diesel engine.
Three changes complicating the overheating problem
Currently, all of these air heat exchangers use the engine raw
cooling water before it goes to the engine heat exchanger. This
will pre-heat the raw cooling water about 20°F to 25°F before it
enters the engine heat exchanger. This increase in temperature was
empirically verified twice with pumps at a high flow.
The raw water temperature increase can be seen with the
composite thermal imaging camera photos below. In the left photo
the incoming raw cooling water temperature at the inlet strainer is
84.2°F, and on the right, the raw water inlet exiting the
combustion air heat exchanger has been increased to 109°F. The
water then makes its way to the engine heat exchanger to cool the
Raw water temperature at Inlet StrainerWater temperature exiting
air after cooler
3. The air from the combustion air heat exchanger is discharging
directly into the engine combustion chamber, therefore the
exchanger must not leak water into the air path.
Even in limited quantities, a non-compressible liquid such as
water that enters a combustion chamber of an engine running at a
high speed, could cause a mechanical failure such that internal
parts are ejected out the sides of the engine. This type of
dramatic mechanical failure has occurred so many times on
reciprocating commercial gas compressors that for the last three
decades every compressor has a special liquid separator on the
inlet that causes an automatic shutdown of the unit if liquids try
to enter the compressor cylinder.
To limit this exposure, the air after cooler exchanger should be
built to contain maximum pump pressure, plus a safety factor, with
no damage. It is unknown what the current design pressure is, but
some of these exchangers are labelled with 60 psi as the maximum
pressure. Typically, the firewater pump supplying this cooling
water could produce water pressures that exceed 210 psi.
Anyone who is involved in an annual pump test should limit the
time spent around, and specifically at the side of, any diesel
We can prevent premature engine failures due to overheating.
A. Record more information and require a longer run time during
the annual flow test.
During the annual flow test, the pump should be operated at 150%
of rated flow point for 45 minutes, but not less than the time it
takes for the engine temperature to stabilize plus 15 minutes. At
the end of the 150% flow time period, with the engine still
running, the following should be recorded for historical comparison
from year-to-year to determine if there is a performance
deterioration of the cooling system:
1. Record the engine water temperature. The closer the
temperature is to 180° F the better the raw water system is
performing. The closer it is to 200° F is an indication of a
2. Record the pressure in the raw cooling water loop, with the
primary system open. Record it again with only the bypass leg open
and then again with both systems legs open.
All three pressures should be about the same. If one side is
lower than the other, there may be partial blockage of the strainer
and/or the regulator, or the regulator could be malfunctioning. If
the pressure is markedly greater with both legs open, both the
strainers and/or regulators may be partially blocked, or the
strainers and regulators are just too small.
3. Record the pressure in the raw cooling water cooling loop
while the pump is at 100% flow point and compare it with the
pressure at the 150% flow point.
If the pressure is more than 3 psi lower at the 150% test point,
the raw cooling water supply piping and/or connection to the system
is either undersized or it is being restricted by some type of
B. The following additional preventive actions should be
1. The strainers should be disassembled and inspected (not just
blown down) before each weekly churn test.
2. During the weekly churn test each engine should be started
several different ways while the ECM switch is on the backup ECM.
Caution: Do not change the ECM switch while the engine is
3. During the weekly churn test and during the annual pump flow
test, visually inspect the raw cooling water outlet at the floor
drain several times to determine if there is a reduced flow from
previous flow test.
4. Install a means to sound an alarm if the raw water flow is
reduced more than 75% of required cooling water requirement.
If a raw water flow alarm is not installed: At least every three
years, the engine heat
exchanger should be internally inspected.
If the heat exchanger is of the welded design and cannot be
internally inspected, it should be removed and the raw water side
should be vigorously flushed in the reverse direction to normal
5. At least every three to five years, a raw cooling water flow
test should be performed. This is the same as required during the
acceptance test of the pump. It is done by disconnecting the
discharge piping going to the floor drain. During the 100% flow
point, a container of a known capacity (typically a 5 gallon pail)
should be used to catch the discharge water so the actual GPM of
raw water is known. The minimum flow rate vs. water temperature
chart for each engine came with the new pump installation
instructions. The water temperature, used to set the minimum raw
cooling water flow rate, should be the maximum water temperature
that can be expected in the hottest months of the year. Caution: If
the engine has an external combustion air heat exchanger that uses
the same raw water system going to the engine heat exchanger, you
may need to add 20°F to the normal maximum high water
C. Consider these items when writing the specifications for a
new diesel powered unit: 1. Fully investigate the choices and do
dismiss a standard radiator type cooling system for any diesel
2. If a water to water engine cooling system is necessary, the
following should be included:
• A raw water low flow alarm that will sound when the flow is
reduced more than 75% of required cooling water flow.
• An engine heat exchanger should be designed to allow for
internal inspection and cleaning.
3. The supercharger compressed air after cooler should be an
internal “inter-cooler” built inside the engine.
If an external air after cooler heat exchanger is to be used,
the raw cooling water source should have a separate connection to
the fire pump discharge piping and should be completely independent
of the raw cooling water system for the engine heat exchanger. This
is allowed in the FM (Factory Mutual) approval standard.
The maximum design water pressure on any external air after
cooler heat exchanger should be at least the maximum water pressure
that can be produced by the fire pump plus a safety factor.
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