Emptying and refilling the MGB cooling System

General

1. Filling the cooling system of post June 1976 MGBs is made more difficult because some parts of it are higher than the Thermostat Housing Filler Plug which is the recommended filling point for coolant so that the fluid fills the system only up to this level, leaving the top full of air. A second problem is the thermostat which, when cold, is closed and has only a very small opening through which all the coolant must flow as you pour.
2. It will make life easier if you lubricate hoses, clips and fittings with a suitable rubber lubricant (eg MS4 silicone grease) before fitting. This makes them easier to fit, remove and manipulate and also helps to prevent corrosion of the steel water pipe fittings. Don’t worry if the hose can still be rotated after normal tightening of the clips; it won’t leak and will firm up later.

Draining the coolant.

1. When emptying the radiator, the instructions given in the MGB Repair Operations Manual do not suggest turning the heater control to HOT but you should do so to make sure that the heater is drained.
2. Use clean vessels for collecting and pouring the coolant so that it can be safely re-used.
3. The manual indicates that the pressure relief cap should be removed before slackening the clip and removing the bottom hose from the radiator. However, if you do all this, water sprays everywhere – except into the vessel you have carefully placed underneath. It is much more easily controlled with the cap left on because the flow of water is much slower and can be directed where you want it ie: into your vessel.
4. Although not generally necessary, if you want to drain all the coolant, you must undo the engine drain plug.

Refilling the cooling system

1. The Repair Operations Manual suggests a rather complicated procedure starting with refilling the system by removing the Thermostat Housing Filler Plug and pouring water through there. If you have ever tried this method, you will know that it is a very slow process, taking ages with much tedious topping-up to fill the system. This is because all the water you put in has to go through a very small hole in the closed thermostat. It is much faster to remove one end of the top hose from the thermostat housing and loosen the clip on the radiator end so that the hose can be rotated to leave the open end pointing upwards (this is where the rubber lubricant helps). Water and antifreeze can then be poured in almost as fast as you can go until the point is reached when a trickle appears coming from the thermostat housing pipe. At this point, stop pouring and replace the hose as quickly as possible before too much escapes.
2. If you are adding antifreeze, it is best to start with about 3 pints (2 litres) of water followed by the correct amount of antifreeze and only then to keep filling with water until the trickle appears. If you start with antifreeze, you will probably find rather a lot of expensive antifreeze escapes, more or less neat from thermostat housing pipe before you can stop it!
3. It also does not seem to be a good idea to follow the instructions in the manual for topping up the Expansion Tank before refilling the system as this merely serves to restrict the flow of air and hence slow down the filling process. It should however, be topped up to nearly full after filling and before driving off. To remove as much air as possible from the system, both top and bottom radiator hoses can be repeatedly squeezed (preferably both at the same time – strong fingers are a great help here!) with the pressure cap still off until the bubbling stops. After this process, some coolant will have been drawn out of the expansion tank and into the radiator so check again whether the tank needs topping up.
4. Once the engine has been run and the coolant thoroughly heated, the air in the system will expand and most of it will find its way out through the expansion tank and pressure cap. As the system cools down again, the liquid contents of the expansion tank will be drawn back into the system to take up the space left by the escaping air so do make sure to check that the tank is at least half full before driving off again.
5. Don’t worry about putting antifreeze in the expansion tank in summer or if you are going to drive the car straightaway; the coolant will become evenly mixed throughout as it repeatedly expands and contracts from heating and cooling of the system. However, if you are about to put the car out of doors into the cold winter night without first driving it , please ignore the above remarks and do put some antifreeze in the expansion tank to prevent it freezing.

Geoff Leggett

Squeaking Rear Springs
The rear springs on my Midget have been squeaking and annoying me. I had sprayed them with WD40 but this did not improve matters, so I tried Waxoyl on the leaves and on the rubbers and at last my springs stopped squeaking.

Mike Malig

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