Posted on: February 21, 2015

by Dick Guthoehrlein

Tiger overheating is a problem familiar to many of us. The following article summarizes some techniques which should help cure most overheating problems.

Before discussing the cures, a quick review of the theory is in order. Starting at the front of the car, the primary objective is to get as much cool air flow through the radiator as possible. The air must be kept in contact with the radiator long enough to accomplish maximum heat transfer. The objective is to transfer the engine heat to the air via the coolant and radiator. The air must then be removed from the area behind the radiator to make room for cooler incoming air. It is also vital that the correct circulation of the coolant through the block and heads be maintained. Here again the cooling medium must remain in contact with the cast iron long enough to accomplish the heat transfer.

Now the cures. First, the airflow into the radiator must be maximized. One simple thing that can be done is to block off the holes behind the horns. This will tend to force more air to flow through the radiator. If originality is not a concern, you can remove the grill bars and emblem. Portions of the splash pan and front apron can also be removed. In extreme cases, the bumper could also be removed. All this cutting and removing can accomplish increased air flow and a cleaner, less turbulent air flow but you will lose some structural rigidity. As such, try the least obtrusive method first.

Now that we have all the air we need, how do we get the radiator to transfer its heat to the air? The first thing to do is to remove any paint from the radiator, especially the fins and tubes. Any paint or foreign matter on the radiator will slow down the heat transfer. The next stage of improvement is to obtain a new radiator with a thicker coil and/or improved design fins. The ultimate would be to recore the radiator with a thicker core and baffle fins. These fins are “S” shaped and provide more surface area for transferring heat to the air.

Next, what do you do with the air after it has picked up the heat from the radiator? In stock form, the air is forced down and around the motor and into the area under the car. A first step is probably to install a fiberglass LAT option hood. This directs fresh air to the carb and provides air vents into the area in front of the windshield. A more radical modification is to cut triangular openings in the sheetmetal in front of and behind the wheel wells, in the vicinity of the windshield washer bottle and the brake servo unit. On a street car, louvers or screen can be used to cover the openings. These holes will vent into the wheel wells where the air is rather turbulent. This modification may not accomplish a great deal. The rearward holes can be vented through the fenders to the outside of the car. A simple triangular box structure can be fabricated for this purpose. Probably the most radical change but also the most beneficial would be the installation of a front spoiler or air dam. At speed, this device will develop a low pressure area under the car. There is an added benefit here. In traffic, where most overheating problems occur, a spoiler or air dam will tend to stop the recirculation of hot air through the radiator. The last modification in this area concerns the fan shroud. Ideally, the front edge of the fan should be even with the rear edge of the shroud. The Tiger has the fan recessed into the shroud. As the fan pulls the air through the radiator, some of the aids thrown off radially by centrifugal force. This air then circulates in the area between the fan and the radiator virtually cutting off circulation through the comers of the radiator. The cure, is to use your tin shears and cut off some of the shroud. Or, if you are a real wizard with sheet metal, you may be able to fabricate a new shroud. If you are that good, you can fill in the bottom of the shroud that is missing from the stock unit.

Another area of consideration is the water pump. There has been much discussion about the use of cast iron versus aluminum pumps, but there is no agreement as to which is best. If your engine is stock and the pump is in good condition, (the impellers aren’t rotted away) either pump should work. If the engine is modified and/or you have a rear end gear ratio requiring high engine revs, the pump may be cavitating, and/or pumping the water through the block too fast. The cure for both problems is to remove every other vane from the impeller.

Pumping water too fast may seem to be a contradiction when you are talking about overheating problems. What happens is that the water is not in the radiator or engine block long enough to transfer heat efficiently. Also, the coolant flow through the engine block can be disturbed. This will cause local hot spots to develop. The same problems can occur in a stock engine if you remove the thermostat. Replace it with a gutted thermostat or a flat plate with holes drilled in it. How many and how big? Cut and try.

Rust and sludge in the block can also cause problems. If the coolant does not come into contact with the cast iron, very little heat transfer will occur. This problem can be prevented by using anti-corrosion additives and by frequent flushing of the cooling system. Use a strong caustic soda solution or any of the commercial products for flushing the system. You can remove the block and have it cooked out, if necessary.

Another area with considerable deviation of opinions is what coolant to use. Opinions range from a 50/50 solution to 100% antifreeze. The consensus is that each car is different and that curing the problem is mostly a cut and try proposition. Things that have worked for one person seemed to have absolutely no affect for another.

If you use all of these tips on your car, you should be able to sit in the middle of Death Valley and idle all day long – well, almost all day!