Oil Air Coolers
Oil to Air
Heat Exchangers and Oil to Water Heat Exchangers
For Mobile and Industrial Applications
Tips and Tricks in Using Oil Air Coolers
1. Temperature Switch:
When using oil coolers, many customers, especially
in the mobile equipment market, believe that there
is a requirement to use thermostats. Dont try
to dissuade them, sell the thermostat, but make sure
they are measuring the oil temperature that is flowing
out of the oil cooler. This is important, otherwise
the temperature re-switch difference of the thermostat
(11°C at 47°
thermostates) will occur ( 47°minus
11°=36°C operating temperature)!
For circulation cooling systems (kidney loop) dont
insert thermostats in the cooler element, but in the
reservoir of the oil cooler. It will not have any
effect in the element because the oil inside the oil
cooler will not be warmed-up if the circulation pump
is not started. The pump/fan will be switched on by
the thermostat when temperature in the reservoir reaches
the set point.
Thermostats must not be used without relays. Size
the relays based on the higher power input ( 3 times
normal power input "in rush current"). Customer
complaints of relay failures are usually because the
relay was dimensioned for normal power input from
2. Check of Calculation:
The cooler calculation sometimes gives wrong results,
if it is done according to the rules. There might
be a intersection between the outlet temperatures
of the fluids, especially in applications with water
and glycol. Compared with oil application the heat
dissipation rate is much higher ( up to 2 times).
Solution: Use of a larger oil cooler or cooler with
the same size but higher airflow, higher number of
revolutions on cooler with hydraulic motors, use of
DC fan units with more power (see S-motors), use several
oil coolers combined in series or parallel connection.
3. Series Connection of PHE:
The calculation is generally done with a computer
program, which enables you to vary the input data
and use different values to influence the result.
Variation of the fins sometimes yields amazing results
in size and cost.
Determination of the cooler design is done by means
of the so-called "Operating Point". This
point is the intersection between the characteristic
lines of the element and the fan. Changes from this
point result in a decrease in efficiency. The same
is true if a second element is mounted in front of
the first element (e.g. stationary motors). Exact
data about power of the fan unit and the decrease
in heat dissipation of the original element has to
be taken into account.
If an adequate second element is mounted to a standard
oil/air cooler you can expect approx. 40% additional
heat dissipation. We recommend using combination elements
(2 independent circuits within 1 element/fan unit).
4. Pressure drop on oil side, depending on viscosity:
All pressure drop curves in our catalog are calculated
with 30cSt and checked. 30cSt means, that the oil
used has, at 40°C a viscosity of 30cSt.
If the oil outlet temperature of the oil cooler is
higher than 40°C, use the table on page 7 of the cooler
catalog for calculation of the real pressure drop
in the element. The present oil viscosity can be calculated
exactly with the viscosity tables you received. For
the transfer from cp into cSt use the following formula:
Recalculation of heat dissipation depending on the
viscosity will be done only with oil of a high viscosity
(ISO VG 150, 220). We have enough reserve, because
the curves are very accurate, they are calculated
first and then checked with our test installation.
Most Italian producers have incorrect curves displayed
in their catalogs.
5. Decrease of heat dissipation in dependence
of the sea level:
The data for the fans was calculated for the complete
fan-unit on the basis of sea level; air flow in kg/sec.
If a fan-unit is not used on this level a correction
factor must be used. The higher the altitude the thinner
the air and therefore lighter. Less kg/sec air flows
through the fan compared to the flow at sea level
which is 1,225 kg/m3.
6. Cooling of water with use of aluminum elements:
Pure water without any additives cannot be used in
an open circuit with aluminum elements. It causes
oxidation inside the element, which will clog the
oil channels. But you can use mixtures of water and
glycol (at least 5% glycol). The glycol will adhere
to the surface of the aluminum and prevent oxidation.
In closed circuits the use of water without glycol
is restricted. It depends on the supply of fresh water
to the closed circuit. (supply of oxygen).
The calculation of the heat dissipation for water
uses the factor 2.5, which means that the required
specific heat dissipation has to be divided by 2.5
before choosing a cooler. Once you have converted
the heat dissipation required you can use the curves
in the catalog, which are designed for use with oil.
Attention, it is necessary to recalculate the outlet
temperatures to avoid intersection!
Formula for difference of water temperature:
x heat dissipation
7. Use of oil coolers in salty environment:
Salty air is very aggressive, permanent conservation
is almost impossible, but there are some methods of
temporary prevention of oxidation- especially for
aluminum parts. The varnish coat of the elements cannot
withstand the salt of the air, that is why a special
coat for the cooler is necessary. Even the hub of
the fan of all coolers with JEC motors are treated
with that varnish. Parts made of steels, like housings,
feet and connection parts, are powder coated or galvanized
and do not need any further treatment. Electric motors
should be applied with a damp room protection. More
effort is not recommended.
Plate-heat exchanger and sea water or salt
water as flow media will dissolve the material of
the fins (1,4404) - battery effect.
8. Use of oil coolers in arctic environment:
The only component that might cause problems is the
fan, which is made of polypropylene, in the arctic
environment it must be made of glass-fibre reinforced
polyamide. The electric motor uses temperature resistant
grease and electric heating to avoid condensation.
A temperature switch should activate the oil cooler.
Practice showed that mobile vehicles in arctic environment
are parked in halls during the night. And the engines
run within the hall till operating temperature is
reached. The danger of thermal shock is relatively
A bypass valve is advantageous during warm-up.
9. Use of bypass-valves:
Bypass-valves are needed to avoid over pressure in
the system, watch the frequency of pressure shocks.
At high frequency and heavy pressure peaks a bypass-valve
is not applicable.
Another possibility is the use of bypass-valves in
applications with low heat dissipation and high oil
flows or temporary oil flow peaks.
The cooler can be designed for the most favorable
oil flow. The present pressure drop for the heat dissipation
(see catalog) and the operating pressure for the bypass-valve
with safety factor (appr. pressure drop x 1.5) have
to be determined.
10. Maximum operating temperature:
The data of pressure can be applied for temperature
up to 100°C.
If there is a need for higher temperatures, the following
schedule is used:
11. Comparison with competitor:
Many producers have in their
catalogs data about heat dissipation which does not
meet reality. They take advantage of the fact that
the data given by customers is not very exact. A test,
which shows whether the data in the catalog meet the
requirements of the customers, is rarely made. If
the oil outlet temperature is 65°C instead of 60°C
does not matter very much. Depending on the oil flow
the difference can be up to 20%. This factor has to
be taken into account as average at many competitors.
Air Coolers | Butterfly Valves
SAE-and CETOP Flanges | Plate-Heat
Exchangers | Contact Us