FS115 - Engine Failure - Major Causes and Their Conditions

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Fact Sheet 115Engine Failure – Major Causes & their Conditions

ENgiNE FAiLurE – MAjor CAuSES & thEir CoNditioNSMost engine failures are directly or indirectly attributable to either engine

overheating or some complete or partial failure of the lubrication system.

these failures can occur over a long period of time and vehicle operation or

they may be sudden and catastrophic.

this often depends on how soon the initial problem is recognised, the mode

of operation at the time, the type and severity of the failure, the condition of

the vehicle at the time and the degree of vehicle maintenance. the mode of

vehicle operation can contribute to the severity of these engine failures and,

in addition, poor maintenance practices can also be a factor.

Engine overheating and/or lubrication problems, if not attended to, can lead

to serious and permanent engine failures. Similarly, some poor practices

may also lead to serious engine problems. the way in which these problems

can affect engine life and performance is outlined in this Fact Sheet.

EnginE OvErhEatingAnything that contributes to the engine running above its designed operating temperature can contribute to

engine failure. the common causes of engine overheating are shown in this table.

Cause ResultBurst cooling system hoses Leading to loss of coolant

Coolant leakage from gaskets/seals gradual loss of coolant

Damaged radiator core resulting in coolant leakage

Radiator core internally clogged with sludge resulting in poor coolant flow and reduced heat transfer

Externally clogged radiator core due to dirt, insects, etc., again resulting in poor heat

transfer

Damaged external fins on radiator core reduced air-flow through radiator

Broken or loose fan belt reduced air-flow through radiator

Faulty thermostat opening at too high a temperature

Faulty electric cooling fan/s reduced air flow through radiator

Radiator coolant dirty and/or past the end of its useful life

Can cause internal cooling system corrosion with reduced heat transfer

Internal engine problems Can cause internal cooling system corrosion with reduced heat transfer Such as leaking head gasket or corroded or cracked cylinder head or block. often this is as a result of one or more of the above conditions – results in heat, pressure and corrosive gases being forced into the cooling system, resulting in loss of coolant and rapid temperature increase


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When overheating occurs, “steam pockets” are formed in critical areas within

the engine. As steam is not a good conductor of heat, it reduces the coolant’s

ability to conduct heat from these critical areas. this can result in localised “hot

spots” in the cylinder head in the vicinity of exhaust valve seats and combustion

chambers and in the cylinder block around the tops of the cylinders. the heat

produced by combustion, is not easily removed away from these areas as the

steam generated is a poor conductor of heat, so the heat continues to build up.

Any heat build-up can be critical in the top ring/cylinder area as these

components rely on an extremely thin oil film for their lubrication. Such an

increase in heat build-up results in reducing the oil viscosity of the extremely

thin oil film lubricating the piston rings and any breakdown of this film will lead to

increased friction and hence the generation of more heat. the end result is that

the piston rings can start to seize in the cylinder bore, producing even more

frictional heat, which then passes into the piston. the result of all this increased

heat is that the pistons eventually seize in the cylinder bores, resulting in either

a completely seized engine or badly damaged pistons, rings and cylinder bores.

Lubricant rELatEd PrObLEmsWhile severe engine overheating may result in seizure of pistons and/or rings in

the cylinder bores, any failure of the lubricant or its supply can result in damage

to many of the engine’s components. Lubricant failure can be attributed to

many causes and may take the form of an interruption of supply of oil to critical

areas, breakdown of the lubricant film, contamination of the lubricant itself,

poor maintenance practices, or the use of an incorrect grade of oil. Common

causes of lubricant related problems are shown in this table.

Cause ResultLow oil level/loss of oil A severe reduction in oil capacity can result in difficulties in oil pick-up by the oil

pump, resulting in oil starvation and interruption of lubricant supply to critical

engine components.

Severe oil consumption – leakage/burning

Extremely high oil consumption can result in reduced engine oil capacity with the

problems already outlined.

Engine oil deposits deposits in the engine oil, either in the form of “sludge” (usually associated with

cold, stop/start motoring) or from oxidised oil (as a result of very severe service)

can cause problems with lubricant supply, due to these deposits restricting oil

galleries and filters. this restriction of engine oil passages results in reduction

of oil supply to critical engine components such as bearings, camshaft and cam

followers, gudgeon pin bushes and piston rings. in these circumstances, wear

and/or seizure of these components are likely.

in addition, this reduction in oil supply may also result in less oil being supplied

to cool the piston “under crowns”, where it greatly assists with piston cooling.

Any reduction in oil supply to piston under crowns results in considerable heat

build-up in this area and can lead to rapid piston seizure.

Corrosion – cylinder head

Cracked cylinder head under cam

Cylinder head

Cracked combustion chamber


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Blocked filter if the engine oil filter is blocked in any way, the supply of engine lubricant is

restricted and engine damage, especially to engine bearings, can occur.

Blocked oil ways/pump pick-up screens

Any blockage of internal oil ways or screens can result in restricted lubricant

supply to engine components and damage will result.

Extended drain intervals Extended oil drain intervals can result in oil deposits from the formation of sludge,

and oil thickening due to oxidation. the engine manufacturer’s recommendations

must not be exceeded with regard to oil drain intervals.

Oil viscosity– too heavy/too light

it is essential at engine start-up that the lubricant be easily circulated within

the engine to provide the necessary oil film for protection of highly loaded

components. in addition, at full operating temperature and under load the

engine oil must be able to retain its film strength to provide complete engine

protection. it is important that the manufacturer’s recommendations regarding

oil quality and its viscosity be adhered to.

Engine component failure Any engine component failure that reduces or cuts off oil supply can result in

wear or seizure of heavily loaded engine components. Such problems as broken

oil pick-up pipe, broken or seized oil pump drive, broken oil pressure pipes (if the

engine is so equipped) and broken oil supply pipes to overhead camshafts are

some examples of engine component failure that can result in severe engine

damage. in these cases, the internal components are starved of oil, resulting in

rapid wear and possible seizure.

the supply of the correct grade of lubricant, in the correct quantity and changed at the correct interval, is

essential for the long-term, satisfactory performance of an engine. As indicated, any interruption to supply

from any cause has the potential to lead to serious engine problems of wear and/or seizure.

POOr maintEnancE PracticEsPoor maintenance practices can also result in premature engine failure. As already mentioned, over-extending

engine oil drain intervals can easily result in filter and screen blockages due to oil deposits. these deposits,

due to either high-temperature oxidation or low-temperature sludge, are kept under control and dispersed in

the oil by suitable additives. however, when the recommended oil drain intervals are exceeded these additives

are depleted and deposits are no longer prevented from forming and can then accumulate in oil passages,

screens and filters where they reduce oil supply.

Welch plug – rusty holeValve lifters – damaged and resurfacedPiston blowby close-up

Engine bearings – worn and new Piston ring – cracked Cavitation erosion Oil sludge - close-up

Oil sludge


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Poor maintenance of engine air filters will also contribute to engine problems, as any blockage of air filters

results in over-rich fuel mixture due to reduced air-flow. over-rich fuel mixtures can result in fuel dilution of

the engine oil and this in turn contributes to increased oil oxidation and, if severe enough, will also result in

reduced oil viscosity with its inherent loss of oil film strength.

Failure to replace the timing belt at the correct interval, usually between 90,000 and 100,000 km, or 3 to

5 years, will result in breakage of this belt. With overhead camshaft engines this invariably results in valves

hitting pistons with dire consequences. the valves are damaged and piston and cylinder head damage can

also result.

driving cOnditiOnsin addition to the factors already mentioned, extreme driving

conditions can also contribute to engine failure in the long-

term. Conditions such as continuous stop-start driving,

contributes to the formation of sludge deposits, which can

lead to problems of filter and screen blocking, with the

resultant reduction in lubricant supply.

Similarly, continuous high-speed driving and/or operation

under heavy load, such as towing large caravans or trailers,

can result in premature oxidation of the engine oil, again

giving rise to deposit formation and the blocking of oil ways,

filters and screens.

overstressing engines can also result in component failure

such as damaged bearings, broken connecting rods, cracked

or broken pistons, broken or “dropped” valves, etc. Such

failures as these usually result in a complete engine “blow-

up”, often where the engine is virtually destroyed as both the

cylinder block and cylinder head are severely damaged. these

extreme driving conditions, if coupled with poor maintenance

practices, such as extended oil drains, will exacerbate the

problems mentioned above.

cOncLusiOnModern engines, properly maintained, give many thousands of kilometres of reliable service. however, even

under ideal operating conditions, with regular and recommended oil change intervals and maintenance,

no engine will last forever. Wear will eventually occur to the highly loaded components within the engine;

however, this wear does not generally result in catastrophic engine failure.

it is the problems mentioned, such as blocked radiators, clogged radiator cores, loose fan belts, inoperative

electric fans, low engine oil levels, high oil consumption, engine oil leaks, etc., that generally lead to sudden

and catastrophic engine failures. if these problems are identified and rectified by regular maintenance and

servicing, this will assist in avoiding the type of engine failures mentioned.

Continuous high-speed driving and/or operation under heavy load, such as towing large caravans or trailers, can result deposit formation and the blocking of oil ways, filters and screens.

Continuous stop-start driving, contributes to the formation of sludge deposits, which can lead to problems of filter and screen blocking, with the resultant reduction in lubricant supply.

FS115 - Engine Failure - Major Causes and Their Conditions

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