Technical Tips

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Extract from April's MGOC publication - Enjoying MG

Beat the Heat

Keep Cool in Summer

Every summer our motorway hardshoulders are littered with classic cars that have boiled over in the summer heat. Such cars normally spend most of the year garaged and although regularly cleaned, polished and serviced their cooling systems have been overlooked. It is worth spending a little time understanding what causes the cooling system to become innefective and what steps can be taken to service the various components and improve efficiency.


The first item to consider is the coolant itself and its effect on the cooling components such as the engine block and cylinder head, the radiator and hoses. The coolant absorbs heat from the cylinders and by flowing through the radiator, becomes cool again, whereupon it recycles to the engine to repeat the process. If ordinary tap water is used, over a period of time corrosion will occur inside the engine and radiator and a build-up of scale and rust will eventually restrict heat transfer and the flow of coolant. The use of anti-freeze containing corrosion inhibitors reduces the problem, however using tap water as a base is not ideal. For many years the Club has recommended Forlife Radiator Fluid, which is used undiluted as a complete coolant, anti-freeze and corrosion inhibitor. It is ideal for classic cars as it protects engine blocks, radiators and cooling hoses whilst running and during periods of storage plus it provides an extra safety margin against boiling over, due to its own high boiling point of 109 degrees centigrade. In practise, apart from stripping the engine to throughly clean the water jacket, using Forlife as a corrosion inhibitor is virtually the only viable option to improve the flow of coolant through the block. Being so versatile, Forlife is used by classic car museumsand racing teams alike.


(includes half pint for heater)

MGB GHN3 10 pints
MGB GHN4 10 pints
MGB GHN5 12 pints
MG V8 16 pints
MGC 18.5 pints

Thermostat & Radiator Cap

These two components control the flow of coolant and the system's pressure, thereby regulating the overall operating temperature. It is important that the correct specification thermostat and radiator cap are used and are working properly. These are inexpensive components and if you are in any doubt, replace them. The following is the correct application for model type:

MGB GHN3 74 7 lbs
MGB GHN4/5 c/b 82c 10 lbs
MGB r/b 82c 13 lbs
MG V8 82c 15 lbs
Midget Vert flow rad 82c 7 lbs
Midget cross flow rad 82c 15 lbs
Midget 1500 82c 15 lbs

Thermostats are available with various operating temperature settings for Summer, Normal or Winter use. The normal setting is 82 centigrade and in practise this should be satisfactory for all year round use in this country. The hot climate option is set to operate at 74c, except for Midget 1500 models, the cold climate option is set to open at 88c. There is no such flexibility however for the radiator caps and it is important that the cooling system is pressurised at the correct level for the particular model.

Rubber Hoses

Most overheating problems are caused as a result of hose failure from either the hose splitting or bursting open. Deterioration of hoses will ocurr either by ageing or by the destructive effect of changing dilutions of anti-freeze. Basically with glycol anti-freeze a constant strength of the correct mixture ratio of water to glycol will not adversly affect the rubber hose, however as coolant is lost and the system topped-up with either water or neat anti-freeze, the balance of the mixture alters, causing glycol to be leached out of the rubber or impregnated further. These changes cause hardening and weakening of the hoses till ultimately they fail. Always inspect your rubber hoses at regular service intervals and replace them if there are any signs of ageing or deterioration.
NB. If your MG overheats, wait until the engine has cooled before attempting to remove the radiator cap, as the water pressure in an overheated engine can cause severe scalding. Also, to protect the engine do not attempt to refill the system with cold water until it has completely cooled.


Radiators require little maintenance apart from the regular removal of insects and leaf debris from the matrix airways. They are however susceptible to deterioration as vibration will stress the inlet and outlet pipes causing cracking, and ultimately the water matrix will become increasingly blocked with corossion and water lime scale. Flushing the matrix will have a limited effect, but these days a reconditioned or replacement radiator is the easiest and the best option. Heater radiator: A useful extra cooling capacity is provided by the car's heater radiator, which is as important in summer for cooling as it is in winter for heating.

Cooling Fans -
Mechanical and Electric

The mechanical cooling fan is powered off the crankshaft by the fan belt and the following checks are worth making periodically. The correct tension of the fan belt ensures that the fan blades are rotating at their optimum speed to draw air through the radiator (note an overtight belt causes excess wear to the water pump bearings). The three bladed metal fan is mounted on four small rubber grommets and as these deteriorate the blades have a tendancy to oscillate and again cause water pump bearings to fail prematurely. Also check that the blades themselves are not bent, thereby greatly reducing their effectiveness.

Later MGB and all V8 models were fitted with electric cooling fans as standard equipment, being more efficient than the mechanical method without the need to waste valuable b.h.p. to generate airflow, before the engine has exceeded its normal operating temperature. The motor (two for V8 models) is fitted in front of the radiator and is activated by an electronic heat sensor switch by the coolants' temperature. This system is far more efficient and for this reason aftermarket kits, such as Kenlowe Electric Fan are so popular and are available for MGA, all Midgets, MGB and MGC models.

Normal Operating Temperature

The ideal position for your temperature gauge is between 7 o'clock position and on the "N", or at 180 F, 82 C. Engines usually find their own operating temperature, so don't worry if your MG is fractionally above or below. Sudden fluctuations should be immediately investigated and cold or hot running temperature will cause inefficient and excessive wear to the engine.

Summer is probably the best season for enjoying your MG, and a few hours spent on preventative maintenance now will keep you in the driving seat and not under the bonnet.


In conjunction with this article our Spares Department has compiled the following offers on items mentioned.

Radiator Coolant
Forlife Radiator Fluid
Five Litres
(add £7.95 p&p up to 20 litres)

Thermostats and Rad Caps
All thermostats
All radiator caps
(add .99p p&p for 1 or both)

Cooling Hose Kits
Complete Kits with hose clips:
MGB up to `72
MGB `72 - `76 (18V)
MGB `76 onwards
V8 model
Midget up to `72
Mid 1275 square heater
Midget round heater
Midget 1500
(add 3.80 p&p)

Radiators New
MGB centre fill type
MGB electric fan model
V8 model
(add £6.25 delivery)

Electric Fan Motors
MGB r/b and V8 Model
(add £3.80 p&p)

Kenlow Electric Fan Kit
Midget 1275 & 1500
(add £4.50 p&p)

Heater Control Valve
MGB models
Midget 1275
Midget 1500
(add £1.99 p&p)

Heater Motors (standard)
MGB, C, V8 models

Heater Motor (High Efficiency)
Kit includes: Motor, large impellor and adaptor plate mounting
(Matrix & or Motors p&p £3.80)

Water Pumps
Midget 1275
Midget 1500
MGB 3 bearing
MGB up to 18V
MGB 18V onwards
(add £4.50 p&p)


To order any of these items, Telephone MG Owners' Spares 01954 230928 or email us.

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