Winter Driving Safety Tip

By Author: JD Durham
Total Articles: 41
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Very few of us today take the time to warm up our vehicles before driving them as they have been engineered to eliminate lots of old problems like stumbling, cold stalling, hanging chokes, etc. So the typical driver hops in the vehicle starts it up and immediately shifts it into gear and starts driving. On the surface this is a good idea as it saves fuel not to mention the time savings for you. It is a good practice most of the time.

However this is the time of the year those living in the Northern Hemisphere should be extra cautious in their driving. Yes, there is the cold plus snow and ice to contend with and that does make it dangerous. There is a bigger danger! The bigger danger is that of an icing throttle which removes your ability to control the speed.

When the temperature is in the 30 to 40 degree Fahrenheit range most people think, that is safe from icing conditions and if they were referencing the road or highways that statement would be true of course except for overpasses and bridges. These are exactly the perfect conditions for an icing throttle.

So what are these conditions and how does this ...
... happen?

The moisture content in the air is not a constant percentage as we all know; sometimes there is an increase from rain, and other times in the form of snow or ice which depends on several factors like outside air temperature and how high the moisture is when it starts falling. These items increase the amount of moisture in the air substantially.

As the air is drawn into the engine it of course passes through the Throttle Body and over the Throttle Plate which in reality is nothing more than a variable orifice. When any gas or liquid passes though an orifice from a larger area of high pressure to a smaller one of low pressure there is cooling taking place at the orifice area. This is the same principle as used in Air Conditioning and you can demonstrate this very easily by taking a warm drink without ice and drawing it into your mouth through a straw. The temperature drops enough that it is noticeable.

Manufacturers over the years have had many approaches to warming up the Throttle Plate in vehicles to make them safer. One of the early things was a Heat Riser, which was simply a thermally controlled plate installed in the exhaust. Later designs used a Thermal Vacuum Control Valve in a coolant passage and a vacuum operated motor attached to the Heat Riser. These designs forced some exhaust gases through passages engineered into the engine that ran to the intake manifold and underneath the Carburetor Throttle Plate. These designs performed two functions; it decreased the amount of time the Automatic Choke was applied and reduced Throttle Plate Icing.

A later design by GM termed Early Fuel Evaporation (EFE), used a thermally controlled electric heating plate installed underneath the Carburetor. This design was most common on the “A” body vehicle with a 3.0 Liter v6 engine and an E2FE Carburetor.

Both of these designs were supplemented by an exhaust heated vacuum motor valve installed into the air cleaner this system was termed Thermal Air Cleaner (Thermac) by GM. It captured the heat from an Exhaust Manifold and routed it into the Air Cleaner to warm the air entering the Carburetor.

Since the move to Fuel Injection by manufacturers in an attempt to comply with EPA requirements and to increase Corporate Average Fuel Economy (CAFÉ) the design has shifted to cooling system passages that either run through the Throttle Body or are very close to the Throttle Body in the Intake Manifold. The previous designs of Heat Riser and Thermac were eliminated as the engineers felt confident of the new systems.

This last design works well enough in most cases, but when you have vehicles that are not maintained properly (coolant changes) or have minor coolant leaks, this is a recipe for stopped up passages or air bubbles in the cooling system. These two conditions fail to warm up the Throttle Plate area properly thus promoting Throttle Plate Icing. Most drivers and many mechanics are not even aware that their cooling system could affect their safety.

So on those days that the temperature is in the 30 to 40 degree range and the moisture content in the air is high, you should allow your vehicle to warm up for at least a minute or two before driving. This is merely a safety precaution that may have been a factor in the previously reported uncontrolled acceleration on Toyota vehicles that was in the news and caused so many injuries.

Copyright © 2011 JD Durham

JD Durham is a World Class Technician, an Automotive Hall of Fame honoree with 45 years experience in the automotive service and repair industry and a staff writer. Visit Straight Talk Automotive for obd bluetooth diagnostic tools, and obd ii software at fantastic pricing.