Ka Kooling
System
A
Cooling System Overview
Modern
car cooling systems have to make the best out of a lot of compromises. Although their primary design remit is to
provide adequate cooling for the engine under all circumstances (Fiat, are you taking note here?). This means anything from sub-zero winters through
to stop / go driving in a hot city at high altitude, running the air
conditioning, having driven at high speed along a motorway before getting stuck
in traffic.
The
cooling system is also used to provide heat for the interior via the heater,
which uses warm coolant fluid for heating.
Radiators require a supply of cool air, either
from the motion of the vehicle travelling forward or from cooling fans (or
both) and coolant needs to be pumped from around the engine block, via a
heater matrix, to the radiator where waste heat is effectively dumped
overboard, before flowing back to the engine block once more.
In
order to accelerate the warm-up process, the radiator is isolated from the rest
of the system via a heat sensitive valve, the thermostat, which should remain
shut until the temperature rises.
It
is reputed to beneficial for the coolant temperature to remain at a reasonably
constant temperature as much as possible to reduce thermal stress on the engine. However, if your engine dies of thermal shock
it has probably a million miles on it!
Some
of the compromises involved in a cooling system include the requirement to warm
up quicker. For a petrol engine this
improves the official Government fuel consumption figures since these are
conducted from cold and petrol engines need the air:fuel mixture enriched when cold. Diesels do not suffer from this affliction,
but instead a modern diesel may take many miles to warm up properly. In both cases, rapid warm up times reduce
some of the other effects of a cold
engine.
The
less the volume of coolant, the quicker it will warm up when cold, but the more
volatile the temperature will be once the engine is up to normal operating
temperature.
The
Radiator Intake
With
regards to the radiator air intake, there are numerous different designs. Most cars have the radiator mounted at the front
of the vehicle. Here it benefits from
the coolest possible air. Vehicles with air conditioning and an intercooler
mount the radiator behind these two plumbing items.
Unfortunately,
having large quantities of air flowing through a radiator is not aerodynamically
efficient and manufacturers use a variety of ingenious solutions. Most cars (including the Ka) use
aerodynamic slats (the more obvious examples include the Mercedes Benz ML
class and Honda Civic), which allow air to enter the grill at both low and
high speed, but deflect much of the air at higher speeds (thus improving the
aerodynamic efficiency). Readers may
be interested to note that Ford pioneered this approach with the original mark
one Fiesta.
Some
cars have relatively low asymmetrical intakes over just the radiator (such
as the Peugeot 106 and the later Duratec-8v Ka) whereas
others have symmetrical intakes, such as the Endura-E powered Ka, illustrated
here.
The
more observant of you will note that the 2003
Ka (and onwards) equipped with the Duratec engine has a different
front grill arrangement - Ford have blocked off part of the grill, presumably
because to do so improves the Ka’s aerodynamics and the cooling air is no
longer required (the manifold now being at the back of the engine bay).
Cooling
Fans
Many
modern cars control their cooling fan(s)
via the ECU. Older cars often used a thermostat to control
the cooling fans, but thermostats are less reliable and harder to control than
using an already integrated component of the car. By way of an example, Kermit had a single cooling
fan with two speeds activated by the ECU.
When running the air
conditioning, the ECU uses the cooling fan at low speed so as to maintain a
flow of air past the condenser and thus maintain air conditioning system
efficiency. This also has the side
effect of maintaining the coolant temperature at around 90°C under normal
circumstances, since the thermostat can maintain the coolant temperature with a
continuous flow of air past the radiator.
From my OBD-II Scanner observations in the Ka,
with the air conditioning switched off the ECU activates the fan at slow speed
when the coolant temperature reaches 100°C.
It switches the off at when the coolant temperature drops to 93°C. When first encountering heavy traffic
conditions, the coolant temperature rises quite slowly from 90°C up to 100°C,
then the fan is switched on, and the temperature drops quite rapidly to
93°C. During the early stages, driving
forward at even a very modest speed (for example, as slow as the Ka will go
in second gear) makes quite a significant difference to the coolant
temperature since it draws cool air through the radiator. However, the longer one spends in high heat
stress conditions, the warmer the underbonnet
temperatures get, and the quicker the coolant temperature rises
back up to 100°C. Even after forty
minutes of very heavy traffic, the coolant temperature has been kept at or
under 101°C.
Even
after spending this long in very slow moving traffic once you are able to drive
off, the coolant temperature drops quite rapidly. If the temperature is hovering around 95°C,
it only takes around hundred metres of driving inside the 30 mph speed limit (including
accelerating to 30) for the temperature to be back down to 91°C.
At
the time of writing, I do not yet know at what temperature the ECU switches the fan over to high
speed, but I would suspect it would be around the 103°C level (and back down
to slow speed at 100°C). I will
update the website with these temperature observations in due course.
Other
Cooling Systems
As
I alluded to above, modern cars tend to use the ECU to control the fans. With regard to my own cars, Danielle and Geoffrey
certainly used a thermostat because these cars didn’t have an ECU! Melissa’s very
active cooling fan was controlled by a little Italian man living under the
bonnet. Lucy’s
ECU did little else but control her single cooling fan. Hoshi’s twin fans were also ECU controlled
with an element of load sensing logic involved, too, very clever.
Kermit’s
Warm Up
This
graph (constructed using data supplied from my OBD-II Scanner) shows Kermit’s coolant
temperature. I started the lad after he
had been parked up for three hours and then ran a couple of errands around
There
are three distinct stages. During the
first initial the coolant temperature is rising very rapidly, even despite the
relatively low load on the engine.
However, once the temperature climbs to 90°C, the rate of change
suddenly decelerates, signifying the second stage. During the second stage, the temperature
slowly increases until we get bogged down in traffic. It then starts to climb before the cooling
fan kicked in at just over 100°C. The
coolant temperature then moved from 100°C down to 93°C.
The
Heater
Modern
petrol cars with all-alloy engines and small capacity cooling systems are exceptionally
quick to warm up following a cold start.
The ECU often deliberately enriches the fuel:air ratio to accelerate the warming up process, too,
whereas with a manual choke it is possible to drive with a leaner mixture (and save fuel). The Ka doesn’t take long to warm up, despite
being disadvantaged by an iron block engine (these take longer to heat up) but it is the Accord that wins the
warm up challenge.
One
of the most useful features of the Ka’s heating and ventilation system only
becomes obvious when you live with a car that doesn’t have such comprehensive
demisting abilities. Fiat’s likeable Cinquecento is one example. In the Cinquecento, when you select the air
direction lever to windscreen, this is precisely
where the air goes. You get no air
leakage elsewhere, so perhaps it’s difficult to fault the Fiat – except it
means that the side windows and footwell get no air
at all. My Fords and the Honda always
provide the side windows with some air when you have selected the windscreen
mode. These systems mean that the car
has an ability to demist the windscreen and side windows under ordinary
conditions.
The
Saab’s automatic air conditioning system handles demisting all by itself and
one very rarely needs to tell it to use the demist mode, but when you do, it’s
very effective!
Diesel
cars usually have three disadvantages when it comes to supplying hot air after
a cold start. The first is that many
diesel engines have an iron block. The second
is that diesel engines do not need to run with an enriched fuel:air mixture when cold. If a diesel engine is deliberately run at a
higher engine speed when cold, this is not caused by a richer fuel:air mixture but is the car simply
running the engine at a higher speed for occupant comfort. The third disadvantage is that diesel engines
run cooler than petrol engines and at idle, produce very little heat. My Fiesta and Mondeo
diesels took seemingly forever to
warm up from cold.
Many
modern diesels have some little tricks to help this cold start no heat phenomenon. The Saab uses an auxiliary fuel heater, which
burns diesel simply to heat up the cooling system. In effect this reduces fuel consumption (it’s burning diesel but you’re not moving). Other cars use electric elements to heat the
cooling system, which are not as effective but don’t have such an adverse
effect on fuel consumption.
Many
cars use an electrically controlled heater valve to adjust the flow of warm
coolant through the heater matrix, including the Ka. Indeed if you have a Ka, Fiesta or Puma and
you hear an occasional ticking or clunking noise from the dashboard with the
heater turned part way between full cold and full heat, you’re listening to the
heater valve. The noise is the valve opening or shutting, and it cycles between open
and shut depending on the heater settings. Note that this valve can fail and the heater
stuck in either the hot or cold settings is a relatively common Ka problem.
Cooling
System Temperature Stability
Some
cars have cooling systems that are seemingly very stable. Once they reach their normal operating
temperature, the temperature typically remains at this level, give or take a
few degrees, unless the driver provokes it (decelerating from a motorway
cruise to then spend twenty minutes in slow moving stop / go traffic works). These systems typically have a relatively
large cooling system capacity and a diesel engine. The Ka - and most Fords - have
this kind of cooling system.
Other
cars have a particularly volatile cooling system. They may take less time to heat up, but the
coolant temperature rises very quickly under thermal stress, and is kept in
check by an active cooling fan. Many
small Fiats have this type of system, as do many MG / Rovers with the K-series
engine. These systems usually have a low
cooling system capacity, which usually confers the advantage of a quicker
warm-up time, but can make the engine rather more volatile to overheating, especially
if the driver doesn’t check the cooling system level.
There
is nothing wrong with either system, providing the driver checks the coolant
level and changes the coolant when needed.
Higher capacity systems are arguably safer should the driver not check
the level, although if this is the case both systems will probably fail.
One
thing I have noticed is that when Kermit’s thoroughly warmed up (like after
an hour of driving), if you turn the heater off (select full cold), you can
temporarily increase the coolant temperature by working the engine hard (such
as ascending a steep gradient) and reduce the coolant temperature by
letting the donk relax (descending the hill on the
far side). Through doing these, you
may see 89°C – 92°C on the OBD-II Scanner
read out.
Ka
Kooling – on the Drag Strip
On
the drag strip circuit, a car’s
cooling system is subjected to three distinct phases. Joining at the queue, which when busy
consists of a number of slow moving cars.
Coolant temperatures typically rise, especially on a hot day with a busy
strip. Once you’re on the line, you’ll
spend much of it holding a high engine speed and of course, when accelerating
down the strip you’re asking the engine to work as hard as possible and
temperatures continue to rise. Once
you’re up to speed, the rush of cool air through the radiator is enough to
bring temperatures down once more. Once
you’ve reached the quarter mile flag, you lift off the power and then begin the
mile and a half drive back to the back of the queue - which is enough to bring
the coolant temperature back down to normal.
At
Crail 2004,
Kermit’s coolant temperature rose to a maximum of 100°C whilst in the queue,
was typically down to 95°C at launch, and was around 93°C at the bottom of the
strip. By the time I had reached the
start of the queue once more, the temperature was either 89°C or 90°C once
more.
Ka Kooling at High
Ambient Temperatures
As
explained here, air conditioning
removes both heat and moisture from the air thus providing the occupants with a
supply of cool, dry air. This makes
driving in warm, muggy weather comfortable rather than hot and sticky.
However,
the heat and moisture removed from the system has to go somewhere. The heat escapes to the environment via the
condenser and the water vapour is turned back into liquid and drains out of the
bottom of the car.
In
almost all cars I’ve looked at and certainly for my own, the condenser sits in
front of the radiator, behind or adjacent to the intercooler and oil cooler if
fitted. Standard 1·3 Kas
don’t have an intercooler or oil cooler fitted at the front of the engine bay,
just the condenser if you have air conditioning.
Using
the air conditioning system reduces the efficiency of the car’s cooling system
because air reaching the radiator has already been warmed by flowing through
the condenser. If the air conditioning
system has been in use for some time on a warm day (from half an hour
upwards) the condenser runs almost as hot as the radiator itself.
This
warm air has to go somewhere and most of it enters the engine bay. I discuss some of the problems of a hot underbonnet temperature here.
The
cooling fan is also used to keep a steady flow of air through the condenser (which
is sensitive to differences in temperature), thus drawing more air into the
engine bay. The warmer the condenser, the
more the compressor must be used to maintain the temperature of air leaving the
system at 4°C. Since the air
conditioning compressor is driven by the engine, when it is in use this
increases the load. More fuel must
therefore be burnt and this is why cars with air conditioning deliberately run
the cooling fan to keep the condenser as cool as possible.
Using
air conditioning reduces the efficiency of the cooling system both directly and
indirectly. Don’t let this put you off
using the air conditioning, though – cars are designed with the additional load
in mind!
All
1·3 Kas of a certain engine design use the same
cooling system and there are no differences between those models equipped with
air conditioning to those without it.
The system is arguably over-specified for those Kas
without it (although there is a strong argument that it is impossible to over-specify
a cooling system).
On
a warm day (where ambient air temperature is over 25°C) it is relatively
easy to see the difference that the air conditioning system makes to both
coolant and intake (or induction) temperatures.
This
one shows the temperatures without air conditioning running.
This
one shows the temperatures with air conditioning running.
These
two charts illustrate the difference in coolant and induction system
temperatures for the same route driven both with and without air conditioning. The ambient air temperature was 27°C on the
day with air conditioning and 28°C without air conditioning. Not the same, but
close enough for my purposes.
There
are some significant differences between the two charts, which I now discuss.
My
Commute
Both
of these charts illustrate a slightly extended commute home for me. I leave the office, drive through Pontefract,
join the motorway and cruise at the speed limit (eight miles of
fifty-limited, nineteen miles of seventy-limited) before driving into the middle
of York along Tadcaster road, past the railway
station, complete one circle of the one way system then get home.
The
final link in
The
Warm Up
There
is very little differentiation between the two charts during the warming up
phase. Both coolant temperature plots
show that the temperature overshot both on the upside and downside before
settling down and this takes just over five minutes for both plots. The cooling system is showing normal
temperature as I join the dual carriageway.
Cruising
Whilst
cruising, we witness the first difference between the two plots. Without air conditioning, the intake
temperature (in red) tends to remain below 40°C. With air
conditioning, it is around 45°C or
higher.
Into
When
we leave the dual carriageway and drive into
There
are two main differences between the two charts. When using the air conditioning, induction
temperatures rise much quicker once we show down and the other is how the
coolant temperature gradually builds.
Without air conditioning, the heat build up is much slower but the
coolant temperature spikes up to 101°C before
the cooling fan kicks in and cools it down.
Conclusions
With
the air conditioning having been running for thirty minutes on a warm day and
the car bogged down in city traffic, the cooling fan at low speed cannot
provide an adequate flow of air to maintain the coolant temperature with the
air conditioning system running.
Without
the air conditioning running, the cooling fan proved able to reduce the coolant
temperature down to 93°C.
If
I were to continue driving around
With
air conditioning running, the ECU would have triggered the cooling fan at
higher speed, which I hope would of reduced the
coolant temperature. If the coolant
temperature was not reduced, the ECU would shut down the air conditioning
system.
Without
air conditioning, over a long enough period of time underbonnet temperatures would have risen, bringing with it
the coolant temperature such that it would start to rise with the fan running
at slow speed. The ECU would then
trigger the fan at high speed, thus reducing the coolant temperature.