Thermac system?

[flyboy1100]

I understand the basis, and i believe it is supposed to try and regulate the temp between 85-115.

My 2 questions are:
when it is 20f outside, will the door in the snorkel open once at operating temp, because mine did not today. It will open when the engine is off

Will that door open under WOT?

 

[89Suburban]

Yes it's supposed to regulate the incoming air temp to between 90 and 130 degrees. The door should yield to higher throttle demands and open as necessary to keep from choking the incoming engine air supply at high volumes. You should be able to test this by watching the flapper door and snapping the throttle hard from an idle to see if it yields.

 

[skysurfer]

The TAC operates via a temp sensor in the air cleaner that regulates vacuum to open or close the door in the snorkel. At 20 degrees, it's probable that the the sensor never saw the minimum temp to open the door. The later units, like the one on my '89, did away with the vacuum motor assy and went to a wax filled pot actuator. As the wax heats up and melts, it expands and opens the door. As the wax cools, it contracts and closes it again.

Edit: I thought that throttle position did not affect tac operation but I found an article that said if vacuum drops below a certain point the door will open.

 

[89Suburban]

I read that if there is enough of a CFM demand the door should be overridden by that demand but I don;t know if that is factual though. Interesting topic as there were a few different ways this system was designed to operate over the years. Do any new cars even use this type of system any more?

I should go test mine.

 

[flyboy1100]

Yes it's supposed to regulate the incoming air temp to between 90 and 130 degrees. The door should yield to higher throttle demands and open as necessary to keep from choking the incoming engine air supply at high volumes. You should be able to test this by watching the flapper door and snapping the throttle hard from an idle to see if it yields.

It didn't when i tested snapping the throttle in the driveway.

Makes me wonder if it opens/operates correctly. Will try disabling it and see if i can feel a difference i guess

 

[89Suburban]

It didn't when i tested snapping the throttle in the driveway.

Makes me wonder if it opens/operates correctly. Will try disabling it and see if i can feel a difference i guess

Maybe you can download this file @chengny posted. It's a service manual and might have something about it in there.

http://www.gmsquarebody.com/forum/showthread.php?t=7627


I'd do it but i am at work right now. I'll have to check my manuals in the garage too and see what I can dig up and post for info in this thread. Great job getting this thread started.

 

[flyboy1100]

I have that, but haven't had time to look through it yet. Was driving....

 

[rich weyand]

It needs engine vacuum to close the cold air door and pull hot air. When engine vacuum falls below a certain point (due to the throttle being opened), the cold air door will open.

You can test that the cold air door is not stuck shut by pulling the vacuum line off the vacuum motor on the snorkel that runs the cold air door. The door should then open.

Another test, if the truck is usually garaged, is to park the warm truck in the garage when you get home. Wait about a half hour for the engine heat to warm the garage, then open the garage door enough to clear the tailpipe and start it up. After a few minutes, the cold air door should open.

 

[GTME94]

Do any new cars even use this type of system any more?

Nothing new that I know of use it. It really is for carburetor heat, with fuel injection no need to get the air warm to help vaporize the fuel. The pressurized fuel from the injectors vaporizes pretty well even when cold.

I've been in the wind tunnel at -40 and both new gas and diesel start up pretty well. New common rail diesels will even start without a block heater as long as you wait for the glow plugs to do their job. we did have the advantage of having a battery charger on the battery for the diesels but nothing else to help get it started.

 

[rich weyand]

Nothing new that I know of use it. It really is for carburetor heat, with fuel injection no need to get the air warm to help vaporize the fuel. The pressurized fuel from the injectors vaporizes pretty well even when cold....

That's correct. A carburetor gives only an approximation of the correct mixture, and it works best at a given inlet-air temperature. That's where the approximation is closest to the correct mixture. Without carb heat, performance and gas mileage in cold weather suffer, sometimes to the point of major suckiness. That's what the thermac does for you. On any kind of injection system, the computer adjusts the mixture to be exact -- not an approximation -- across a wide range of variables, including inlet-air temperature.

 

[flyboy1100]

You can test that the cold air door is not stuck shut by pulling the vacuum line off the vacuum motor on the snorkel that runs the cold air door. The door should then open.

That part works for sure on mine.

I will have my wife Rev the engine and i will watch the door when it isn't blowing 40mph with snow.

 

[flyboy1100]

That's correct. A carburetor gives only an approximation of the correct mixture, and it works best at a given inlet-air temperature. That's where the approximation is closest to the correct mixture. Without carb heat, performance and gas mileage in cold weather suffer, sometimes to the point of major suckiness. That's what the thermac does for you. On any kind of injection system, the computer adjusts the mixture to be exact -- not an approximation -- across a wide range of variables, including inlet-air temperature.

While true, there is benefit to be had from using a warm air intake in the winter with fuel injection. On my subaru i can almost achieve summer mpg with my WAI. It raises inlet temps by 50F so it really helps when the temp gets subzero

 

[89Suburban]

Ok I see comments about fuel injected systems not needing this, but they exist on all squarebody and GMT400 TBI motors that I ever saw. I am guessing that when they went to MPI it was taken away. Can anybody confirm or deny this? We're Vortecs all MPI? Did any of them have the stove pipe on them?

 

[skysurfer]

Wet intakes (carb & tbi) had TAC, mpi doesn't need it.

From Wiki: Heated air intake systems operate on the principle of increasing the temperature of the airױ, the fuel will more effectively stay in suspension in the air rather than falling out of suspension and forming droplets on the floor of the manifold. Warm air from the outside of an exhaust manifold is drawn up into the air cleaner to increase the air temperature as quickly as possible after the engine starts. The air cleaner assembly incorporates a thermostatic vacuum switch that responds to the air temperature after the air filter element and actuates a vacuum motor that moves the control flap to allow the air to be drawn from a cooler location such as the top of the engine bay or outside the engine bay. If the air becomes too cold, the thermostatic switch will automatically change back to drawing heated air from around the outside of the exhaust.

The system was often used with computerised carburettors or throttle body injection systems but is typically not used with multi-point fuel injection, as the problem of fuel falling out of suspension does not occur when the fuel injectors are located close to the inlet valves.

 

[89Suburban]

There ya go.