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The temperature of the fluid in the cooling system can exceed 100 degrees C so it is hot. It is strongly advised not to do anything with the cooling system unless it is cold. Scald’s hurt. Further, the water is under pressure - hence it can exceed boiling point - and will vent out when caps and such are removed. So do not play around with a hot system. There is only one safe way of working on the cooling system of a hot engine and that is to wait until it cools.
Overheating is a symptom, not a problem in itself. The first difficulty in curing the problem is finding out what has gone wrong.
Make sure that the car is in fact overheating. For early Land Rovers and TVRs the dials are best considered for guidance only. If the needle in the temperature gauge has always been hovering on the red without any other symptom, then just run with it. If the change has been progressive then this is the time to do some research.
The advice that, if you have a problem then change the pressure cap seems to be universal and, as the cost is quite low, is probably sensible to follow.
There are two main types of problem: those where there is fluid loss and those without.
NO FLUID LOSS
Although I have no wish to patronise, I do suggest you check that the radiator is not obstructed in any way. It is remarkable how leaves can cover a grill in autumn and pieces of paper can take up a very high percentage of the cooling area. So always check first. It could be a fault with the cooling fan(s). If your vehicle is a bit long in the tooth then the fan belt may be slipping. Whilst a screech is often present, and can be definitive, its absence should not be taken as confirmation that the belt’s tension is correct. Check it!
A fan’s fluid coupling may well be faulty and always check that electric fans come on before the fluid boils.
If a car overheats at times of high demand, such as when heavily loaded, towing, hill climbing or when at high altitude, or in heavy traffic, then it could be a problem with the system. Establish that the ignition/injection timing is spot on, and the fuel mixture is not weak. The thermostat may not be opening – this is a easy thing to check but they are cheap enough to change if they become a little aged.
A kinked hose can restrict the flow of fluid to a surprising extent.
A radiator has a limited life expectancy and not one that is necessarily measured in years. Any debris that comes loose in the engine’s internals can find its way to the capillaries and end its roaming there and, over time, restrict flow enough to cause overheating. It’s difficult to check at home and one depends on the honesty of the person checking. Recored rads are not cheap and it can be very depressing to pay out £hundreds only to find that it has made no difference.
The cause of the overheating may have nothing to do with the cooling system. For instance, if your brakes are binding or, if you have a new engine fitted, then clearances are not up to spec. The former is easy enough to check but don’t be tempted to touch the drums or wheels but this should only be attempted by those with asbestos fingertips.
Note: the word water is used throughout this article to denote the cooling fluid. This is not strictly accurate as it is probably either 50% water and 50% anti-freeze or 100% anti-freeze.
The cooling system on the Rover V8 and the Speed 6 is ‘industry standard’. A closed pressurised system is used with circulation via a belt driven impeller. This moves hot water from the engine and heater into the radiator. Once cooled the water is then used to cool the engine.
To run efficiently an engine needs to be within a certain range and to lessen the time taken to warm up, a thermostat is used. When the water is below the lowest point in the range it remains cold and the water is diverted directly to the engine without going through the radiator. Further, it is also directed through the heater so you should feel a little bit of warmth before the radiator gets to work. It has been suggested, by those who do not suffer from the cold, that the heater should be switched off until the engine reaches working temperature. Some hopes.
When the prescribed temperature is reached the thermostat opens and the hot water then goes through the radiator to cool.
The engine will have a water jacket. This is the area around the swept volume of the pistons and the head where the water circulates. In the RV8 ‘dry’ liners are used. What this means is that with the liners removed the water jacket remains intact. If for any reason water is allowed into the area between the bore and the liner, water can be forced up the jacket and into the bore. A way of overcoming this is to use flanged liners. RV8R hopes to cover this next month.
To stop fluid seeping in between the joint between the head and engine block a gasket is used. If this gasket fails then water can seep into the combustion chamber or to the outside of the engine block. In the former event a certain loss of compression can be measured.
Water will corrode aluminium so there is an ‘inhibitor’ in anti-freeze which stops this corrosion, or at least lowers it to an extent where it is no problem.
The weak points in the cooling systems are few:
The thermostat.
If it fails in the open position then the engine will take considerably longer to warm up even, in certain conditions, not allowing it to reach working temperature at all. If it fails in the closed position they the engine will overheat fairly quickly.
The pump
The pump is driven via a belt in the same manner at the alternator. This puts loading on one side of the bearing and this will mean that it will eventually fail. This often lacks drama and the first symptom is a small leak from behind the pulley where the collapsed bearing has caused the seals to fail. There is no urgency for replacement: i.e. is does not mean breaking your journey to your auntie, but it should be replaced as soon as possible as a total failure can occur.
The bearing can seize, especially after the car is laid up for a while, but the noise from the fan belt, a tremendous screeching, gives sufficient warning, and the bearing can collapse completely which will mean that the drive belt will stop working so the alternator will not be driven and the red light on your dash will come on.
Pipework
The pipework that carries the water to and from the radiator and heater can fail. Often this is due to rubbing on some other object so check the run. It can be due to age. Upgraded pipes can be bought, look extremely nice and will probably last the life of the car. A weakspot is the joints. If there is a certain degree of seepage then this can point to a failure. Whenever replacing pipe, also replace the Jubilee clips.
The radiator
This can block up or become fractured.
Fans
Some fans are driven in the same way the water pump is and these bearing can also fail. The fan may have a viscous coupling, one which allows the fan not to increase revs beyond a certain limit. This can fail either by not slipping or slipping all the time.
TVRs and most Land Rovers installations have electric fans. These are switched on and off by a thermostatic switch, often called an otter switch, which works from the temperature of the water as it comes from the bottom of the radiator. The connectors can become faulty, the switch can fail and the sensor can lose its sense.
Waterpump on a pre-serpentine Rover V8. The black pipe, arrowed, is the outlet to the heater matrix. The waterpump gasket can be seen as a fine brown line at the back of the pump unit. This can fail with age but this is normally to do with corrosion from not having the proper anti-freeze:water mixture.
Overheating
Cooling system - an overview
FLUID LOSS
Source identifiable
If you can see water emerging from the engine or its ancillaries then most of your diagnostic problems are over. There are a number of favourite locations for leaks.
If you can see water seeping out between head and block then it is a fair assumption that the head and gasket need to be assessed.
The water pump is belt driven and this puts unequal pressure on the pump bearing so is a frequent failure point. Water tends to drip out from behind the pulley. Replacement of the whole unit is the only option and the opportunity to change the thermostat should also be taken.
Core plugs are those circular discs used to blank off the machining holes in the block and they can leak. Replacement is the only option.
The various water pipe junctions are a frequent source of leaks. The pipes flex to an extent and this can cause failure. It can be a very small hole and it might only leak under pressure. Further, if a pipe touches any object, even another pipe, this can wear away the rubber. The complete length of pipe must be checked and a mirror can come in handy to get to those places you eyes cannot reach.
No source
If the water level drops but no water drips or stains can be identified then things become interesting. However, first of all check inside the car to see if the heater matrix is leaking. If not then it would appear that water is disappearing into the engine in some way.
Check the oil dipstick. If the oil has a sort of greyish colour then there is water contamination and the probable cause is a failed head gasket. As the RV8 has the camshaft in the block, head removal is a simple enough operation. The most common causes of a head gasket failure is erosion of the water tubes and a ‘warped’ head. However, the warping is often caused by the engine overheating and far from being the main cause, is, in fact, a symptom.
The lack of greying in the oil tends to indicate a more serious problem.
Engines over 3.5 litres are bored out (apart from the original North American 4.4) and this can lead to a porous block. Water seeps through the block into the gap between the liner. Pressure then pushes the fluid up to the top of the liner and into the combustion chamber. Another cause can be a slipped or fractured liner. All these faults require major work. This would be an opportune time to have flanged or ‘top-hat’ liners fitted which can overcome this problem and limit the chance of its reoccurrence.
The lack of greying in the oil tends to indicate a more serious problem.
Engines over 3.5 litres are bored out (apart from the original North American 4.4) and this can lead to a porous block. Water seeps through the block into the gap between the liner. Pressure then pushes the fluid up to the top of the liner and into the combustion chamber. Another cause can be a slipped or fractured liner. All these faults require major work. This would be an opportune time to have flanged or ‘top-hat’ liners fitted which can overcome this problem and limit the chance of its reoccurrence.
