Top Twelve Things to
Diagnosing Overheating Problems
... plus 4 more
1. RADIATOR CAP:
The cooling system of an engine is designed as a
sealed system with the engine coolant held under pressure. When
under pressure, water and engine coolant boil at a higher
temperature. As your coolant and water increase in temperature and
approach the boiling point, the state of the liquid begins to change to
a gas, seen as steam. A gas is much less efficient in cooling your
engine than a liquid. So increasing the pressure increases the
boiling point, allowing the coolant and water to do a much better job at
removing heat. Keep in mind that internally coolant running
through the channels within the engine will come on contact with metal
that is well above 210°
F so preventing the coolant from boiling is essential. By
increasing the pressure, you are increasing the boiling point and the
coolant remains in a state of liquid rather than converting to a gas.
Heated coolant also expands so a closed loop system will require coolant
to be held in rather than boiled out. A closed loop system will
also need an overflow tank which is reclaimed upon cooling of the
of the Radiator Cap
A functioning radiator cap will maintain its rated
pressure. Different vehicles require different pressure ratings so
check your owners manual for the correct cap for your vehicle. A
periodic check of your radiator cap is important especially when
troubleshooting a cooling problem. Allow the engine to cool
to the touch and remove the radiator cap. Check the radiator cap gasket. The gasket is located on the
underside of the radiator cap. The gasket seals the cooling
system keeping pressurized coolant in the closed loop system. Inspect this
gasket. If it is hard, cracked or split, or if the rubber is brittle or
missing then it should be replaced. A bad cap can be the reason
for lost fluid. A bad cap that is not tightly sealing in cooling
fluid can allow the fluid to boil off, especially when the engine is
shut off. The reason for this is un-circulating fluid will not be
cooled in a hot engine and can increase in temperature as it sits, high
enough to boil. The effect of this can cause fluid to be pushed
out of the radiator via the radiator cap. If the cap is properly
sealed it will be pushed into the overflow tank. If the seal is
damaged or missing it can spill out of the system. If the gasket
is weak or damaged, it will not hold the pressure necessary to maintain
a higher boiling temperature. Always make sure you have a good
cap, an overflow tank and never fill your overflow tank beyond the
'cool' high mark. Also
keep in mind that your cooling system may be leaking pressure somewhere
else other than the radiator cap.
2. WATER/COOLANT LEVEL:
It should go without saying but check your fluid
level. Is it full when the engine is cool? Check the coolant
manufacture's information (usually on the container) for the proper
Coolant / Water ratio as well as your vehicle's maintenance book.
Coolant should always be mixed with water, preferable distilled water,
because water displaces heat better than coolant / antifreeze (coolant
and antifreeze are one in the same) however the coolant / antifreeze boils
at a higher temperature than water alone and freezes at a lower temperature than water.
Most manufactures recommend a 50/50 mix of water and coolant. This
ratio can vary dependant on your region and expected temperatures.
Coolant also lubricates and prevents corrosion and rust in your system.
Straight water will rust the inside of the engine block's coolant
channels and will not provide
lubrication to the water pump. Rust is death to a radiator as it will clog
the channels. Rust is also damaging to critical water jackets in the engine block.
plugs in the engine block are not rust proof will
also rust causing leaks or a quick ejection of your coolant at some point.
Engine coolant does degrade over time so it is
recommended that coolant be changed every few years. Check with
your vehicle manufacturer for recommended intervals.
3. RADIATOR HOSE:
The radiator hoses should be in good shape, not
cracked, brittle or leaking. Hose clamps should not be over
tightened so that they cut into the hose. Other than obvious
damage, hoses can restrict coolant flow. Check the routing of your
hoses. Make sure they are not routed in a way that causes kinks, pinches
or sharp bends causing a partial or
complete blockage. Flexible accordion type hoses will restrict the
flow and should be avoided.
Another cause of overheating can be a weak,
collapsing hose on the suction side of the radiator, usually the lower radiator hose.
Located inside of the hose is a spring. The spring is
usually located inside of the hose. It's job is to prevent the hose from collapsing.
Check this spring and verify that it is in place and that it has not
rusted away or simply broke allowing the hose to collapse. In many
cases the hose will not collapse until the engine is at higher RPMs or
the coolant is hat high temperatures. In some cases a stuck
thermostat can cause a hose to collapse so check that as well.
The thermostat is a valve located in the cooling
system of an engine, which is closed when the engine coolant is cold and
opens gradually in response to the engine heating and thereby
controlling the temperature of the coolant and rate of coolant flow through the engine
block. When you look at the flow of coolant through an engine, the radiator is
the critical component in cooling the fluid in the cooling system.
Coolant must flow through the radiator to be cooled and then back through the block to collect more heat from
the engine, then flow back to the radiator to be cooled again. The
thermostat is the device that is governing this flow. Asside from a small
amount of water that may flow through the bypass hose, the water must flow
through the opened thermostat to get to the radiator. Thermostats are rated
by temperature. Typically a thermostat begins to
open at the rated temperature of the thermostat but it is not fully opened
until the temperature is 10 to 15 degrees above the rated temperature.
So in a sense a thermostat is not an open or closed valve but rather a
device that allows a certain amount of coolant to flow depending on the
temperature of the fluid. A thermostat that is not opening soon
enough or not opening up at all will cause an engine overheat or run
higher than normal. Removing your thermostat all together is not a
good solution to a faulty thermostat since the engine must reach a
certain operating temperature to run efficiently. Removing your
thermostat can be a temporary fix however in an emergency. You can
test a thermostat by hanging it in a pan of water on the stove (not on
the bottom of the pan) and monitor the water temperature and observe the
thermostat. It should open fully at 10 to 15 degrees above it's
5. FAN BELTS:
The coolant must move to be cooled. This is
the job of the water pump. The water pump is driven by the fan
belts or serpentine belt. If the coolant doesn't move, coolant
within the engine
block gets very hot and is not replaced by cooler fluid from the radiator
resulting in a quickly overheating engine.
Most cars on the road use a serpentine belt. A
serpentine belt is a
single belt that drives all the engine accessories. If a serpentine belt fails, all engine
accessories will stop turning. That includes power steering, air
conditioning compressor, alternator, and of course the water pump.
Unless you have an electric fan, the fan belt that drives the water pump also drives the fan.
If you are the do it yourselfer, it's important to carry a spare belt and learn the
proper way to install it. Don’t over tighten v-belts.
6. WATER PUMP:
The water pump, pumps the coolant through your
system. A typical sign of a failed or failing water pump is bad is
typically a leak. A leak is typically occurring through the seal and bearing.
Leaks will commonly present themselves on the
underside of the pump. Most pumps have a small hole below where the
seep out if the seal or bearing have failed. Commonly it is the bearing
gone bad and the seal quickly follows. If your pump is leaking in this
replace the pump as soon as possible. Pump life depends heavily on maintenance of
the cooling system. Scheduled flushing and changing of the coolant at regular intervals
should help the water pump last for the life of the engine. In some
cases a high flow water pump may be the solution to an overheating
problem, more particularly when performance modification have altered
stock configurations of the vehicle. High efficiency water pumps
from Flow Cooler, Edelbrock, Weiand, and
Summit will move more GPM (Gallons Per
Minute) of water than a stock pump. Keep in mind that this may not solve
the original problem or solve the overheating problem.
7. FAN CLUTCH
The fan clutch is a coupling device that is located between
the water pump shaft and the fan. The fan clutch is designed to
improve the vehicle’s cooling system efficiency while reducing the load
on the engine and loss of energy caused by the fan itself. The Fan
Clutch allows the fan to operate at lower speeds and effectively detach
at higher speeds when the vehicle is moving and air movement due to
velocity aids to cool the engine.
There are two types of Fan Clutches, thermal and non thermal
fan clutches, also called centrifugal clutches. Both types operate
on the fluid-drive principle.
Symptoms of a Worn / Defective
Fan Clutch that
should be Replaced
How do you know when your Fan Clutch is wearing out or has
failed to do it's job? There are a few key symptoms.
- Excessive Free-Wheeling when spun manually (when engine is
stopped) - With the engine stopped, manually spin the fan. If
Fan spins excessively, over 3 revolutions, as though there is no
resistance it should be replaced.
- If your air conditioner does not perform well at idle or low vehicle speeds
then the clutch may have failed and air is not passing over the A/C
condenser efficiently enough to cool the refrigerant.
- If the fan speed does not increase when engine is running hot
or if the fan speed does not increase until engine is excessively hot.
- Looseness of the Fan - Excessive lateral movement of the
fan blades. If the fan blade moves more than 1/4" front to back
measured at the end of the blade. Some lateral movement is
a normal condition due to the type of bearing used in fan
clutches. Approximately 1/4" (6.5 mm) maximum lateral movement
measured at the fan tip is allowable.
- Vibration - Sometimes vibration can be detected due to a
failed clutch. The vibration can increase with with engine speed.
Many times this can lead to water pump failure.
- When the engine is stopped, turning the fan blade manually
turns rough, grinding or does not turn at all.
- Leaking silicone Fluid - Excessive fluid leakage will
cause the clutch to fail to engage.
- Noise - If you hear excessive fan noise or a roar at all
engine speeds. Noise can be detected when the clutch should be
engaged, during initial cold startup or when the engine is hot.
Under high speeds or higher RPMs over 2500, a locked up fan can create
a roaring noise.
More about the Fan Clutch
8. Fan Shroud
The fan shroud directs the air from the fan,
directly into the radiator making the fan efficient. A missing or
damaged fan shroud will direct air from the fan directly through the radiator.
Since it is this moving air that absorbs and removes heat from
the radiator and the fluid inside the radiator, a properly fitted, intact
fan shroud is important . If there is not enough air is moving through the
radiator to sufficiently cool the fluid, the result is an overheated engine.
The opening in the fan shroud should be just
slightly larger than the fan's diameter. The shroud should also cover
about half the fan blade width. The fan shroud should also encompass
a full 360
degrees around the radiator and fan. A partial fan shroud is
allowing air to escape and thus not directed into the radiator.
Obviously the radiator is the key component of any
cooling system. Without it, the heat would not efficiently escape
the system. Several factors of a failing radiator can affect
cooling. Leaks in a radiator can cause fluid to escape and reduce
the amount of cooling potential. Look for leaks below, on the sides and
in the front and rear in the fins. Even a small leak can have
negative effects in the long term. As a rule of thumb it is better
to fix a leak or replace the radiator rather than use "Fix-a-Leak"
concoctions that can plug other things such as cooling ports in the
block, channels in the radiator or the thermostat. Corrosion is
another key factor in a failing radiator. Corrosion in the
radiator can block ports or channels in the radiator that flow from one
side to the other. Even if you can look down into the radiator,
the corrosion may be at the lower end and out of sight. Running
straight water in the radiator will allow scale and minerals to build
up, blocking ports. Dirt and mud over the fins of a radiator will
have a big impact on overheating. If your radiator is clogged, so
get the hose out and clean your radiator from the backside if it is
clogged with debris. Be careful not to damage the fins or channels
of the radiator while cleaning it. Damage is also factor.
Damaged or bent over fins can restrict air flow allowing hot coolant to
pass through without dissipating enough heat.
10. DIRTY / GREASY ENGINE:
Though it's a less cause, sometimes every little
bit helps. Dirt on an engine can act as an insulator, much like a
blanket. So can mud and if you are a 4 wheeler like we are, you
occasionally get mud on the engine. A dirty or muddy engine will run hotter.
Not by much but a little. Incidentally, chrome accessories are like heat shields keeping the heat inside your
engine. On the flip side, aluminum is a good conductor of
heat and it will actually take heat out of the engine. Dirt and mud
will have more of an impact on overheating if your radiator is clogged,
so get the hose out and clean your radiator from the backside if it is
clogged with debris.
An automatic transmission will cause an engine to run hotter then a
standard transmission. An engine turning an automatic transmission is
always turning the torque converter whether or not the vehicle is moving. A
torque converter is actually never in neutral and
creates a constant load on the engine causing it to run hotter. An automatic
transmission will also generate more heat internally than a standard
transmission. Some of the heat will be dissipated through the engine
block causing additional heat in the engine. Installing a good transmission cooler
will remove some of the heat from the transmission. The location
of the transmission cooler is also a factor. If it is located in
front of the radiator, heat removed from the transmission via the cooler
will pass over the radiator so factor that in when installing a
12. HEAD GASKET:
A head gasket is a gasket that sits between the
engine block and cylinder head in an internal combustion engine. Its
purpose is to seal the cylinders to ensure maximum compression and avoid
leakage of coolant or engine oil into the cylinders. Overheating
problems due to the head gasket may be due to the Head gasket having a break in it.
Depending on where the break is, you may
not see coolant in the oil but the hot coolant may be mixing with cooler
coolant and raising the temp. Or possibly the coolant may be entering the
combustion chamber and it is burned off resulting in the need for more
coolant. If coolant is entering the combustion chamber you may not see
it if there isn't much passing through the head gasket however it can
still affect temperature. In mild cases you can buy some time with
some sort of leak stopping
Overheating problems due to the head gasket may
also be due to a break in the head gasket that is allowing combustion gasses to be pushed into the coolant.
Depending on you engine configuration and the location of the water
pump, the result could be trapped air in the water pump. Air can get
trapped in a water pump stalls the pump and because automotive water
pumps are not "air tight", they cannot always self prime. This
could also explain a loss of coolant. As the engine cools and when the
engine goes through the exhaust stroke, coolant is pushed into the
combustion chamber. Some guys I know ran without the cap to
hopefully allow the water to not build up pressure and push back into
the cylinder but usually the result of that is a lack of "back pressure"
in the coolant and the combustion gasses leak into the coolant at a
faster rate. Apparently there are better water pumps to prevent air from
stalling them. A guy I know would stop his car and wait, sometimes he
tried rocking the car to get the air bubble out of the water pump, then
start it up again and it would cool quickly. Ultimately a head
gasket replacement is necessary. Again some sort of stop leak may
help and buy some time.
Head gasket condition can be inspected by checking
the compression pressure with a pressure gauge, or better yet, a
leak-down test. Also note any indication of combustion gasses in
the cooling system. Oil mixed with coolant and excessive coolant loss
with no apparent cause, or presence of carbon monoxide or hydrocarbon
gases in the expansion tank of the cooling system can also be signs of
head gasket problems. Driving with a blown head gasket can cause
additional extensive damage due to overheating or loss of lubrication.
OTHER CONTRIBUTORS TO ENGINE HEAT
Too much friction. Change your engine
oil on a regular basis to reduce
internal engine friction. Synthetic oil and some additives aid
to reduce friction. An engine that had been severely overheated at
some point can warp parts, creating severe friction to the point where
it will barely run. Thinking of an old Ford Comet I once owned.
14. Engine Compartment Overcrowding
Over crowding under the hood with lots of accessories in the engine compartment will retain more
heat. A large engine crammed into a small
engine bay will not allow good radiant release of heat.
15. Engine Tuning and Boring
Proper Engine Tuning. The fuel / air mixture,
timing, and spark all affect engine temperature. An improperly
tuned engine can produce more heat.
An engine that has been bored over
the stock bore can run hotter because of the reduced wall thickness of
the metal in the block. Less metal means less metal to dissipate the heat.
Typically this is not a problem unless
the bore has gone overboard in removing metal or the block has been
bored too many times.
16. Engine Color!
Color - OK, now you’re laughing, but the color you paint your engine
matters. I’m told that black is actually the best color for dissipating
heat from the engine. Don’t ask me how this works, I don’t know.
Here's Why black paint works best at
dissipating engine heat