Cockpit Heat

By Norman Nock

Originally published in the Austin-Healey Magazine, January 1992


Heat, altitude, and long climbs are what you can expect when driving to Breckenridge for the International Austin-Healey meet August 17-21, 1992. Getting you there comfortable and getting back is going to depend on how well you prepare your car and the steps you take to insure the comfort of you and your passenger. Here’s a run-down on many of the known problems that have caused Austin-Healey owners to have words with their cars, along with some suggested preventive medicine. (The parts and tools you need are listed in the April 1982 Healey Highlights, page 8. See also April 1989 Chatter, page 9 and August 1990 Austin-Healey Magazine, page 11.)


COCKPIT HEAT


Cockpit heat has long been a standing joke among Healey owners, but in Nevada and Utah outside temperatures can reach 100°F, and the smallest bleed of hot air from the engine compartment will not be funny. Keeping the cockpit of your Healey cool was discussed in the April 1986 issue of Healey Highlights, Page 10.


Here are some key points:


1) It’s very easy to see how heat from the engine compartment gets into the cockpit by putting your car into a dark garage, removing the seats and carpets and aiming a floodlight at the firewall. Now get into the cockpit and take a look at all the light coming through. That’s heat. Jack the car up and shine a light from the bottom and down the inside of the driver-shaft tunnel. That’s more heat.


… look at all the light coming through. That’s heat


To stop the heat, you have to plug these holes. Check the sealing rings on pipes and wires coming through the firewall and replace them if they are missing or in poor condition. The transmission tunnel cover and the vertical plate that is part of the firewall on early Healeys may also need sealing and the insulation replace. Be sure that all the screws that hold these plates and covers are in position and secured tightly. Use silicone adhesive to seal off smaller holes, and check the gearshift boot for holes or tears. Replace if necessary.


Remember, pads won’t solve the problem if you haven’t blocked the holes in the firewall.


2) A Healey's exhaust system is also a prime source of cockpit heat. Inspect the insulation pads around the driver’s footwell in the engine compartment. If these are not in good condition the floor will get very hot. To keep muffler heat away, fabricate an insulation pad to fit under the driver’s seat. Remember, though, pads won’t solve the problem if you haven’t blocked the holes in the firewall.


Here’s another suggestion for those panning to drive to Breckenridge this summer: Keep an adjustable spray pump in the car so you can spray a fine mist of water over your face, arms and legs. Now that the passengers are comfortable, we will move to the car.


ENGINE HEAT


Your engine temperature on the gauge should read about 190°F. If the temperature gauge starts to climb above this and is not stopping, stop your car before you cause major engine damage. Do not exceed 210°F.


Here are some other tips to insure your engine isn’t afflicted with heat exhaustion this August.


The boiling point is a function of atmospheric pressure, and becomes lower as altitude increases.


1) First, understand that the amount of heat that an engine can dissipate is proportional to the difference between the temperature of the liquid coolant in the engine and the temperature of the outside air that carries heat away. The higher the boiling point of the coolant, the higher the efficiency of the cooling system. The boiling point is a function of atmospheric pressure, and becomes lower as altitude increases. At seal level, water boils at 212°F: at 5500 feet it boils at 202°F. Breckenridge is approximately 9,600 feet above sea level. Interstate 70 passes through Vail Pass leading into town at 10,600 feet.


2) Remember too, that the water pump will develop a suction of the intake side, which further reduces the atmospheric pressure at this point. In other words, even thought the car may be operating at a safe 180°F boiling can occur at the pump inlet. Causing expansion of the coolant (vapor lock) and slowing down circulation. This expansion also forces water out of the overflow, and thus the remaining amount of liquid overheats more easily.


3) The chance of vapor lock on the inlet side of the pump is increased by partially blocked radiator cores and by rust scale. If you have not had your radiator overhauled recently, this should be first on your list of jobs to be done.


4) Check your pressure cap. For each additional one pound of pressure, the boiling point of water in the cooling system is raised three degrees. That means that water, which boils at 212°F at sea level will boil at 233° with a 7-pound cap. At 15,000 feet it will boil at 215°F. All big Healeys have a radiator cap that is 1 inch deep. Caps from most other cars will measure ¾”.

If you use a shorter size cap on your Healey the system will not be pressurized, and the coolant will evaporate without any sign of a leak.


5) Don’t use 100 percent antifreeze. Most owners use a 50/50 mixture of antifreeze and water. Maximum protection occurs at a concentration of 70% antifreeze. Increasing the amount of antifreeze above this will actually result in lowering the boiling point.


6) Verify your temperature gauge. To insure you’re operating within the correct temperature range, verify your gauge and be sure it’s not giving you an incorrect reading. To do this, start your engine from cold and let it idle. Insert a thermometer in the top of the radiator and compare it with your gauge. They should read about the same. (Note that since the engine coolant temperature pickup is in the radiator of BN1 to BN6 Healeys, your temperature gauge reading can vary from 160°F to 190°F depending on the ambient temperature. In BN6 to BJ8 Healeys the pickup is in the head. Temperature will then stay about 190°F since the gauge is reading engine temperature.)


7) If after you have checked all items above, and you still have an engine that runs too hot, then the only answer is a big fan like the plastic Hayden fan #3602 available at most auto parts stores and known as the Texas Cooler, or the highly polished six-blade stainless steel/chrome Flex Fan. (For more information on engine heat see Healey Highlights, May 1982, page 11 and July 1981, page 4 and Chatter, November 1988, page 12 and June 1987.)

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