An E-Type that runs hot

Question

First, is the engine actually hot?

This is not a formality. The commonest complaint on an E-Type is a hot gauge, and a hot gauge is not the same thing as a hot engine. Between the coolant and the needle sit a sender, a voltage stabiliser, a length of loom and at least one earth, and any of them can put the needle where the coolant is not.

Do not spend money on cooling parts until this step is settled.

Answer this

• I have measured the coolant temperature independently and it is genuinely highGoes to: When does it run hot?
• I am going by the car's own gaugeGoes to: Verify the gauge before anything else
• It has boiled, pushed coolant out, or lost coolantThat is a different question and it comes first.Goes to: It has boiled or lost coolant

Question

When does it run hot?

This single question separates airflow faults from water flow faults, because the fan matters at a standstill and is close to irrelevant at speed.

Answer this

• Only stationary or in slow trafficAirflow through the radiator is the first suspect.Goes to: Does the fan run, and does the air reach the core?
• Only at sustained speed, or under sustained loadThe fan is doing nothing useful at speed, so this points at flow or at heat input.Goes to: What do the hoses tell you?
• Both, in all conditionsGoes to: Hot in all conditions
• Only in the minutes after switching offGoes to: It only climbs after switch-off
• It is a Series 3 V12 and one bank runs hotter than the otherGoes to: One bank hotter than the other, Series 3 V12

Finding

Verify the gauge before anything else

Why this follows. The gauge, its sender, the voltage stabiliser and the earths are all in series with each other. A fault in any one of them moves the needle without the coolant moving at all.

What to do

• Measure the actual coolant temperature independently, at the thermostat housing or the top hose, with an infrared thermometer or a probe.
• Compare that against what the gauge is showing at the same moment.
• If the car has a Lucas voltage stabiliser feeding the instruments, check it. A tired stabiliser moves the fuel gauge as well, so a fuel gauge that also reads oddly is a strong hint.
• Check the instrument earth. A poor earth raises indicated readings.
• Check the sender's connection and its earth path through the block.

Where next

• I have now confirmed the engine is genuinely running hotGoes to: When does it run hot?

Read further: Instruments and switches, Earths, wiring and the loom

Finding

It has boiled or lost coolant

Do not open a hot pressurised system. Let it cool first.

Why this follows. Coolant leaving the system is either going out of a leak, or being pushed out by pressure the cooling system is not generating on its own.

Two very different faults produce the same symptom, and separating them is the whole of the job here. Either the system is losing coolant to a leak, or combustion gas is entering the coolant and pressurising it. The second is a head gasket question and no amount of radiator work will fix it.

What to do

• Look for external leaks cold and then warm: hose joints, the water pump, the radiator core and its seams, the heater take-offs, the header tank and its cap seal.
• Check whether the system pressurises quickly from cold. A top hose that goes hard within a minute or two of a cold start, before the engine could plausibly be hot, points at gas entering the coolant.
• Look for bubbles in the header tank with the cap off and the engine running, and for a persistent smell of exhaust in the coolant.
• Check the oil for emulsion and the coolant for oil, though the absence of either proves nothing.
• A cylinder leakage or combustion gas test is the test that settles it, and it is worth paying for before buying parts.

Where next

• No coolant loss and no sign of pressurisation. The engine simply runs hotGoes to: When does it run hot?

Read further: Head gasket failure, The cooling system

Question

Does the fan run, and does the air reach the core?

At a standstill the only thing moving air through the radiator is the fan, and the only thing making that air go through the core rather than around it is the cowling and the undertray.

Answer this

• The fan does not run at allGoes to: The fan is not running
• The fan runs, but only once the gauge is already highGoes to: The fan is cutting in too late
• The fan runs, and runs early enoughGoes to: The air is going around the core, not through it

Question

What do the hoses tell you?

At speed there is plenty of air, so the question becomes whether the coolant is moving, and whether the radiator is actually shedding the heat it is given.

With the engine hot and running, compare the temperature of the top hose against the bottom hose. What matters is the size of the difference between them, not either figure on its own. This is a rule of thumb for narrowing the search, not a specification.

Answer this

• The top hose is hot and the bottom hose is much cooler, a large differenceGoes to: The radiator is working, so look at flow rate and heat input
• The top hose is hot and the bottom hose is nearly as hot, a small differenceGoes to: The radiator is not shedding heat
• The engine is hot but the top hose never gets hotGoes to: The thermostat is not opening

Question

Hot in all conditions

When the car runs hot both stationary and at speed, the fault is more likely to be in the fundamentals shared by both conditions, rather than in airflow or in flow rate alone.

Answer this

• Take me through the hose comparisonIt is still the fastest way to separate radiator faults from flow and heat input faults.Goes to: What do the hoses tell you?
• The system is losing coolant or pressurisingGoes to: It has boiled or lost coolant
• Neither, everything is intactGoes to: Work the fundamentals, in this order

Finding

It only climbs after switch-off

Why this follows. With the engine stopped there is no pump moving coolant and no fan or road speed moving air, so heat already in the metal migrates into static coolant. A rise after switch-off is normal in some degree.

The question is whether it merely rises, or whether it boils and pushes coolant out. The first is the physics of the car. The second is a fault.

What to do

• Establish whether coolant is actually being expelled, or whether only the gauge moves. If nothing leaves the system, there may be nothing wrong.
• If coolant is expelled, check the pressure cap first.
• Check the coolant mixture, since a weak or waterlogged mixture boils sooner.
• Check the system is full and free of air.
• If the car has an electric fan on a thermostatic switch, consider whether it is wired to be able to run after the ignition is off, and be aware that this is a modification rather than the original arrangement.

Read further: The cooling system

Finding

One bank hotter than the other, Series 3 V12

Why this follows. An asymmetry between banks is not a radiator or airflow fault, because both banks share the radiator. It points at something that differs between the two banks.

This node applies only to the Series 3 V12. The V12's cooling system has less margin than the six-cylinder cars and a great deal has been written about it, much of it about symptoms rather than causes.

What to do

• Check for an ignition fault confined to one bank. On Lucas OPUS this is worth eliminating early.
• Check the two Zenith Stromberg pairs against each other. A mixture difference between banks puts different heat into each.
• Check for an air lock confined to one side of the system, and check the bleeding procedure was followed.
• Check the exhaust manifolds and their heat shielding, and whether one side is running visibly hotter externally.
• Confirm the asymmetry with an independent thermometer at both banks rather than from a single gauge sender, which reads only where it sits.

Read further: V12 cooling and overheating, Lucas OPUS ignition on the V12, The four Zenith Stromberg carburettors

Finding

The fan is not running

Why this follows. A fan that does not turn removes the only source of airflow the car has at a standstill, which is exactly the condition being reported.

What to do

• Confirm the fan motor itself runs by feeding it directly, so that a dead motor is separated from a dead supply.
• Check the thermostatic switch, by bridging it with the ignition on and seeing whether the fan starts.
• Check the relay if one is fitted, and its supply.
• Check the fan's earth. This is a common failure and costs nothing to inspect.
• On a car with an added electric fan, check that it is wired to a supply that can carry it and that it is not sharing a marginal earth.

Read further: The charging system, Earths, wiring and the loom

Finding

The fan is cutting in too late

Why this follows. If the fan only starts once the gauge has already climbed, the system has no margin left by the time cooling begins, and any queue will beat it.

The archive has not been able to attribute a factory operating point for the fan switch on any series or market, and figures for it circulate widely without a named source. Treat this as a relative judgement about your own car rather than a specification to work to, and confirm against the workshop manual for your car.

What to do

• Establish at what indicated and actual temperature the fan currently starts, using the independent measurement from the first step.
• Inspect the thermostatic switch and its connections. An old switch drifts.
• Consider whether the switch is the correct part for the car, particularly on a car that has been rewired or had a radiator changed.

Read further: The cooling system, Overheating

Finding

The air is going around the core, not through it

Why this follows. A fan can only pull air through the path of least resistance. If the cowl, the undertray or the surrounding sealing is missing or damaged, the easy path is around the radiator rather than through it.

Jaguar itself treated this as a real limit rather than an owner myth. The Series 2 introduced an enlarged front air intake and twin electric fans, which is the factory conceding that the earlier arrangement had little to spare.

What to do

• Check the fan cowl is present, complete and sealing to the radiator.
• Check the undertray. A missing undertray changes the pressure distribution under the nose and is frequently absent on restored cars.
• Look through the radiator core against a light. Silting, bent fins and a core packed with forty years of road debris all block air without looking dramatic.
• Check for anything mounted in front of the radiator that was not there originally, including oil coolers and air conditioning condensers.
• Check the radiator core externally for flattened fins from pressure washing.

Read further: The cooling system, Overheating

Finding

The radiator is working, so look at flow rate and heat input

Why this follows. A large temperature drop across the radiator means it is shedding heat perfectly well from the coolant it receives. If the engine is still hot, either not enough coolant is passing through, or more heat is going in than the system was designed to remove.

What to do

• Check the water pump. A corroded or eroded impeller moves far less coolant than an intact one and gives no other symptom.
• Check the fan belt tension, since a slipping belt underdrives the pump as well as the dynamo or alternator.
• Check for a collapsing bottom hose, which restricts flow only when the pump is pulling hard, so only at speed. Look for a hose with no internal spring, or a soft one.
• Check the thermostat is the right one and is opening fully rather than partly.
• Check ignition timing. Retarded timing puts heat into the engine and is free to check.
• Check mixture. A weak mixture runs hot, and on triple SUs that usually means carburettors that have drifted out of balance rather than a single fault.

Read further: The ignition system, Triple SU carburettors, The cooling system

Finding

The radiator is not shedding heat

Why this follows. If the coolant leaves the radiator almost as hot as it entered, the radiator is not doing its job, whether because the core is blocked internally, blocked externally, or not receiving air.

What to do

• Feel across the face of the radiator for cold patches once hot. Cold areas indicate blocked internal passages.
• Consider the core's history. A radiator that has never been out of the car in sixty years is a suspect regardless of how it looks.
• Have the core cleaned and flow tested, or recored, by a radiator specialist rather than flushing it in the car and hoping.
• Check the core externally as in the airflow branch, since a blocked core blocks air as well as water.
• Check the coolant itself. A system run on water, or on a mixture that has long since lost its inhibitors, silts the core from the inside.

Read further: The cooling system, Modern fuel and E10

Finding

The thermostat is not opening

Why this follows. If the engine is hot and the top hose is not, coolant is not reaching the radiator at all, which is what a thermostat stuck shut does.

What to do

• Remove the thermostat and test it in hot water, watching whether it opens and whether it opens fully.
• Check the thermostat is the correct type and orientation for the car. A wrong or reversed unit restricts flow even when it opens.
• On a car where somebody has removed the thermostat entirely, be aware that running without one can make matters worse rather than better, because coolant can pass through the radiator too quickly to shed heat properly.
• Check the bypass arrangement is as it should be.

Read further: The cooling system

Finding

Work the fundamentals, in this order

Why this follows. These are the items that affect the system in every condition, and they are ordered cheapest and most reversible first.

What to do

• Coolant level, and the mixture. An inhibited mixture at the correct strength raises the boiling point and protects the core. Plain water does neither.
• The pressure cap. A cap that no longer holds pressure lowers the boiling point of the whole system, and it is the cheapest part in the chain.
• Air in the system. An E-Type filled carelessly holds air, and an air pocket at the sender gives a hot reading and poor transfer at the same time.
• Ignition timing and mixture, as heat input rather than heat removal.
• The water pump and the belt.
• The radiator core, cleaned and flow tested by a specialist.
• The gauge and sender, if not already proved in step one.

Read further: The cooling system, Overheating, The ignition system