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Overheating - and how to tame it

(This article is a consolidationfrom multiple contributors in MOT.)

  • Steve Baker
  • Wes Stewart

Steve Baker's advice:

There are many causes and remedies of overheating in classic Minis (especially those with larger engine sizes).

Here is a list of things to try and to check:

    * It's possible that your thermostat is stuck - put a thermometer into the radiator and run the car up from cold. You should be able to see the water in the radiator is not flowing until the thermostat kicks in - and suddenly you'll be able to see the water flow. Note the temperature on the thermometer shortly after that happens - it should match the temperature that the thermostat is designed to kick in at. If it doesn't - replace the thermostat.

    * Use a 'low temperature' thermostat that opens at lower temperatures. The Mini takes pretty standard thermostats that you can buy in any car parts store.

    * In many types of car, removing the thermostat so that the radiator is cooling the water all the time is a good 'quick fix' for overheating. You car takes longer getting up to a proper operating temperature - which is bad for gas consumption - but otherwise it works. But not in the Mini!! The shape of the thermostat helps guide the flow of water around the engine block and ensures that the water does not go only down the 'path of least resistance' but flows through all the holes in the block. Simply removing the thermostat can make overheating problems much worse - and can even damage the block. If you want to take out the thermostat, you have to replace it with a special 'blanking tube' (sometimes called a blanking sleeve) that makes sure the water flows the right way.

    * Remove the temperature gauge sender unit and test it using cups of water ranging from cold to the engine's maximum safe operating temperature. Clean or replace as necessary. This should also give you a good idea of what your temp gauge will show for various temperatures in the engine - and especially, let you know where "normal" is on the gauge.

    * Remove the radiator and flush it several times with commercial radiator cleaner - keep flushing until the water comes out clear. You can also flush the block itself - there is a little drain hole that's opened by a screw on the back of the block especially for this purpose...again, keep flushing until it's clear.

    * Switch to using a 'tropical fan' - this has fewer blades, inclined at a steeper angle. They are noisier than the regular fan - but produce much better airflow. Make sure your fan is mounted the right way around - it's easy to get them on backwards.

    * Consider switching from antifreeze to plain water mixed with commercial "water wetter" (which you can get in any car parts store). Antifreeze doesn't transfer heat as efficiently as plain water - but 'water wetter' is needed to prevent corrosion from plain water and also to lower surface tension and prevent bubbles of steam from forming where the water contacts the block. Here in Texas it doesn't often freeze long enough or hard enough to demand antifreeze...especially if your car is garaged.

    * Running with bad timing or incorrect carburettor settings can cause the engine to run hot - make sure all of that stuff is set up correctly.

    * Some of the older Mini radiators were of an inefficient '2-core' design. Modern 3 and 4 core radiators are better - and there are also more modern 2-core designs that do a better job than the stock radiator. There are some expensive aluminum radiators available that some Mini owners and Mini racers have had good luck with.

    * In older Mini's, the radiator is mounted sideways in the car - there are a set of ventilation slots that take the hot air out into the wheel well behind the front left wheel. Make sure that the slots in the bodywork behind the wheel aren't blocked with mud or grass.

    * Another somewhat non-traditional method to aid in cooling, especially when the above has not helped (and problems have been fixed or eliminated) is to add an automotive heater core or oil cooler into the cooling system, mounting it behind the grill. This is often needed on hot (souped up or race) 1275cc+ motors.

    * One reason, some say, large bore 1275cc motors tend to overheat is that when the 1275 block is bored out drastically the walls between cylinders gets quite thin and heat transfer gets to be a problem in hot climates especially.

    * One other fix is to add an electric fan in the wheel well.

Overheating is almost always the result of multiple problems - so you may have to attack several or even all of the above to get your car to stay cool in the extremes of Texas heat.

Wes Stewart's advice:

I recommend:

    * Super two core radiator
    * High capacity water pump
    * Mr. Gasket thermostat (get the V8, chevy blazer one) -- it has a sleeve design that promotes excellent circulation
    * Tropical 6 blade fan

In triple digit heat, my cars are just fine. A supplemental electric fan in the wheel-well is not a bad idea either for instances where your car is not moving fast enough to promote good air-flow.

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