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The purpose here is to help people recognize that:Intake icing can occur at temperatures up to 70 F.
Intake icing can kill you (stuck throttle+major accident).
Intake icing can occur and mysteriously never be recognized or identified. Many people say they can do this mod because they never drive in cold weather. To them I say that the range for intake icing can run from 20F to 70F with the presence of humid air. This is because of the drastic cooling effect present in the intake. Actually the risk is probably higher above freezing because warmer air can hold more moisture. The hazard below 20F is minimal because the air is so dry. If you don’t think you ever drive in conditions conducive to icing, chances are good that you are seriously mistaken. Three NASCAR drivers died in 2000 presumedly because of stuck throttles (Adam Petty, Kenny Irwin, Tony Roper). A few of the drivers that have had known stuck throttle accidents are Bobby Labonte, Jeff Gordon, Dale Jarett, and Jason Jarett. I’m sure there are a lot more. Now the cause in most cases is undetermined and presumed to have been obliterated or undone by the wreckage. But my question is, if stuck throttle accidents are so serious, why is it that NASCAR has not come up with a design where the throttle can’t get stuck? Why have there been so many of these accidents occur? The problem with icing is that the evidence can quickly disappear. The reason that icing is not suspected is probably because of the popular misconception that freezing temps are required for it to happen. Wrong, wrong, wrong. Of course if I it happens to me I can just shut off the ignition. But then there’s the loss of power steering and the possible loss of control. No matter how you react to the problem, it could still have deadly results. For those using a TB coolant bypass, the odds of a serious problem are really extremely slim. But with the possibility of very serious consequences, is that a risk worth taking? To those who say they have never had a problem, I ask how do you know? Chances are that any erratic engine operation would be blamed on the more typical causes and the real cause would go unrecognized. If an accident occurred, who would ever suspect it as a cause? The odds might be a million to one for anyone here ever being hurt because of this. But is that a lottery game worth playing? PREACHING MODE OFF. Here’s some additional reading for those inclined to learn a bit more on the subject. Here’s some comments about this mod on a C5 Corvette: "The throttle body, as described above, moves a lot of air, at very high velocities, in conditions of vacuum. The laws of physics state such a condition will rob heat from the surfaces in contact with this flow. In conditions of humidity, ice may form at the critical location of the throttle butterfly, freezing its ability to move (translate this ice induced paralysis into an inability to close the throttle). Throttle stuck open, car and engine accelerating, sharp curve ahead, and you want to decelerate…do you see a potential problem here? The purpose of that coolant tube is to prevent "icing" of the throttle body. "But Al, I only use my C5 in the warm weather." Great, I like it warm too. So does your throttle body. Icing can occur at temperatures well in excess of "freezing" ambient temperatures. Two NASCAR accidents (one resulting in a driver fatality) in Brookline Mass this summer were attributed to "stuck throttles", most likely ice induced. This is a modification, that in my opinion, provides no benefit, and a very real possibility of a serious derivability control issue. Don’t do it!" Source: [ http://naturalglasscorvette.com/c5modstoavoid.html ] Here’s another believer: "car engines are susceptible to icing. It has to do with the drop in temperature caused by the faster flow of air near the air input to the carburetor, combined with amount of moisture in the air."... " Some of the old clunkers I used to drive didn't have all the correct parts sometimes, and it gets exciting when there's enough ice buildup to prevent your throttle releasing when you try to decelerate." [ http://yarchive.net/air/carb_ice.html ] Another quote: "I've had a throttle hang and it's the worst feeling a driver can ever have," Jarrett said. "I told my son Jason, he's had it happen twice already, I told him he's experienced the worst thing, that and fire. It's just the most helpless feeling, especially on these shorter type racetracks where you have no banking. Your first reaction is to stomp on the brakes and that basically doesn't do anything when you're going wide open. So it's a terrible feeling." [ http://www.tennessean.com/sii/00/07/09/throttle09.shtml ] More from Popular Mechanics for what you may think it’s worth: "My car will lose power at the strangest times. It usually happens on rainy days, but sometimes not. I'll be traveling along on the freeway -- it doesn't usually happen in traffic -- and the car will just gradually slow down until it stops. It won't restart for about 5 minutes, and it runs rough for about a few seconds after it does start. Sometimes the gas pedal seems to stick open a little, but the engine doesn't run too fast -- it barely runs at all. Needless to say, my mechanic says he can't find anything wrong with the fuel injection or the ignition."
SARAH CLEMSON
MENOMINEE, MI "You've got carburetor icing -- which might seem hard to swallow, as you don't have a carburetor. But you do have a throttle body on your fuel injection, and it's freezing up with atmospheric moisture.
How can this happen, you ask, if the air temperature is in the 50s, and there's no rain? The temperature of the air whistling past your throttle plate drops considerably as the pressure drops from atmospheric pressure (14.7 pounds per square inch) to a vacuum. Why? It's high-school physics -- as the pressure drops, the temp goes down. And as the temp and pressure go down, so does the air's dew point, the point where the moisture drops out. And if it's cold enough, moisture drops out as ice. Ice is what's choking off your engine's air supply, and that's what's making the throttle stick".
[ http://www.popularmechanics.com/automotive/sub_care_clinic/2001/1/car_clinic_9409/print.phtml ]
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