Keeping Your Cool in a Tiger

An Article by Dan Walters
September, 2001

Page 6

The Wrap-Up:

....Wrapping up this series on the cooling system, there are a few other parts of the cooling system to cover.

Temperature Gauge System:

.....I have yet to see accurate, and therefore useful, information about the Sunbeam temperature gauge and related components. Even the shop manual gives incomplete and misleading info! In the Cooling System section of the shop manual, there is no mention of the instrument voltage regulator. In the Electrical Equipment section, the description of operation is incorrect and the testing procedure of the instrument voltage regulator would show all regulators to be "faulty" at one time or another! Correct function of the instrument regulator is necessary for the temp gauge (and fuel gauge) to be anywhere near accurate.

.....The shop manual has a somewhat accurate schematic drawing of the instrument regulator. The regulator has a bimetal strip surrounded by a heater winding, similar to the temp gauge. At one end of the bimetal strip is a contact point, the other end is connected to the output or "I" terminal. When the bimetal strip is cold, the contact point touches another contact point that is connected to the input or "B" terminal. When power is applied to the regulator, both the "B" and "I" terminals have the same voltage and current flows through the heater winding to the regulator case ground. When the bimetal strip heats up, it bends and the contact points separate and voltage is removed from the "I" terminal also current stops flowing through the heater winding. When the bimetal strip cools, it bends back to it's original position and the contacts touch. The cycle is started over again with the heater winding heating the bimetal strip and both "B" and "I" terminals have the same voltage.

.....As you can see by the above description, after the regulator starts to cycle, the output of the instrument regulator is anything but constant. If you check the output of the instrument regulator immediately after turning on the power, you will measure very close to battery voltage. The regulator may take several minutes before it starts to cycle. Probably the best and easiest way to check the function of the temp gauge and instrument regulator is to connect a volt meter between the temp sender and ground. The main thing to verify is pulsing voltage within a few minutes of power turned on.

..... This description of the Voltage Regulator system is based upon the original equipment, as supplied with the car. Replacement units may differ significantly. The voltage regulator on your generator, and early alternator designs (non-solid state) worked in similar manner, though handling much more power, as their size indicates. Newer solid state designs have been built, and circuits made available, by both Tho Smit and Cullen Bennett (who uses independent regulators for the gas and temperature systems.

Gauge Accuracy

.....As far as temp gauge accuracy goes, there are a lot of ways to check it but not very much you can do to adjust the accuracy. As long as all of the components are correct and functioning properly, you should have reasonable accuracy. Real world checks of the temp at thermostat opening and boiling water are good indicators. I think of the stock temp (and fuel) gauge reading as relative and not absolute.

Editor's Note: This isn't Rocket Science, you know. It's either hot, or not, full, or go get gas. What else do you need to know?

.....So, how hot is too hot anyway? The simple answer is when there is a problem. Some of the time it is the driver that has the problem not the car. To expect a car to run cooler than is reasonable, considering the hardware, is to create a problem where none exists. Just because you WANT the car to run at 180 F and it runs at 200 F doesn't mean there is a problem (with the car). The temperature that the cooling system of the car can safely operate is usually higher than the driver feels comfortable with. If we use an example of a typical car (most likely NOT a Sunbeam) with a 50/50 water/antifreeze mix, a 13 pound pressure cap and an accurate temp gauge. A strong case can be made that 230F is a good temperature to run all the time. And a constant 240F is not a problem if the cooling system is in excellent condition. It should be pointed out that coolant temperatures above the non-pressurized boiling point depend directly on the ability of the cooling system to maintain pressure and a relative measure of safety. The above example assumes that the cooling system temperature is maintained by a thermostat and that a worse case scenario (stop and go traffic) would not greatly increase the temperature. In other words, the cooling system is not close to it's limits. The point is that high temperature alone is usually not a problem, it may be a symptom. The key is to be realistic about what is a temperature problem with the car and what is a temperature problem with the driver.

.....A problem is when you continuously lose coolant. A worth while addition to any old car is a coolant recovery system. The key part of a coolant recovery system is a double sealed pressure cap that allows access to the cooling system only through the vent hose. With the vent hose end submerged in a reservoir of extra coolant, the expansion and contraction of the coolant in the radiator tends to purge the cooling system of air and maintain a constant coolant amount in the system under a wider range of operating conditions. Also, a coolant recovery system will reveal leaks in the cooling system by failing to purge the air from the cooling system and/or the loss of extra coolant in the recovery reservoir.

.....Keeping your cool in a Sunbeam is an ongoing battle. We'll try to keep up with all the efforts. Down the road, technology will help but it may be harder to to stay on track. Has anyone tried that "40 Below" stuff yet? It's some pricey potion!

Dan Walters - Happy Tiger Motoring!

The End!