What temp does the manifold heat flap open at?

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DodgeLad

DodgeLad

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Was 32* today and nothing. I checked the actuator with vacuum and it works. Thinking the thermostatic switch mounted in the air cleaner doesn't work right. It's a 1980 truck with a Holley 1945.
 
This info is probably buried in the emissions section of the service manual. I don't remember anymore, but it's over 130 degrees or so F if I remember correctly
 
130*?
I thought it was supposed to open when it was cold out.
I mean the flap in the snorkle of the air cleaner.
 
The thing by default feeds heated air to the air filter bonnet. As the air temp warms up, the stat shuttles the flapper to the open snorkel, if that is what you are calling "open."

You don't want cold air into the snorkel with the engine or air cold for driveability

This is out of the 73 pass car manual, but they all work somewhat the same. I was a "little off" about the temperature LMAO

heat.jpg
 
Nice diagram, Del. Cool find.
 
Thanks very much.

It hardly ever gets to 10* here. I guess it's working as it should.

edit
I reread it and it should be partially 'open' in the morning. It may have been and I did not notice. I was looking for complete open. Plus I am sitting at idle and it says it only works at road load throttle positions.
 
Like I said, that is out of the 73 manual. Yours may work a bit different, the principal is the same........warm air for a quicker warmup when cold, then gradually opening to colder "snorkel" air when warmed up.. This was all for emissions

If you find a good source for downloading more manuals.........I'd like to hear about it
 
Checked it this morning. Mid 30s outside. After starting and at idle, the flap was *slightly* open. I revved her up using the throttle cable and the flap opened up the whole way. Let off throttle, the flap closed some to the slightly open state. Results could be repeated.

Unless someone thinks otherwise, I believe it is working exactly like the manually states.

I think I need to play with the choke adjustment some more. It's a third party electric choke. Feel free to school me on that adjustment.

Thanks again
 
Look I don't think you understand. What I posted was meant 'generally.' Out of the 73 book is the latest info I have that can be easily posted. What you need is to find a factory manual correct for "what you are working on." There might have been a few things changed, LOL, between 73 and 80. In addition, emissions specs were less stringent between the car lines and "heavy" half tons and heavier. Side note, that is the reason "heavy" half tons were invented..........to skirt the emissions regs and put a truck into what would normally be a 3/4T emssions class "back then."
 
DodgeLad said:
Checked it this morning. Mid 30s outside. After starting and at idle, the flap was *slightly* open. I revved her up using the throttle cable and the flap opened up the whole way. Let off throttle, the flap closed some to the slightly open state. Results could be repeated.

Unless someone thinks otherwise, I believe it is working exactly like the manually states.

I think I need to play with the choke adjustment some more. It's a third party electric choke. Feel free to school me on that adjustment.

Thanks again
Click to expand...
Not sure which way you mean is 'open' in your description... more heat from the heater shroud, or more cold air from the snorkel? The way this should work is that:
- With cold air temps: At cold idle, the flap should move to shut off cold air via the snorkel and admit more air from the heater jacket. When you open the throttle, the flap should move to admit more cold air through the snorkel.
- With warm (enough) air temps: The flap should shut off all heated air from the heater jacket and only allow fresh air from the snorkel in, regardless of throttle position.

If the flap is moving it says that the thermostat flows air, and the vacuum lines are good, but that does not tell you if the thermostat is actually working right. You can only know that when the under-hood air temps are warm enough to cause the flap to move to admit only snorkel air regardless of throttle position. So you'll have to warm the car up to test that or wait for a warm day.
 
I need to gather more data. By open I mean the flap lets manifold air in.
 
OK, sounds like the flap is working as it should. You just need to warm it up to see if the flap goes more and more open, which would say the t-stat is working. The t-stat won't care if the warm air is from the environment or the heat riser jacket; if the car warms up for a while and draws air from the heat jacket, the flap should open (to snorkel air) while idling due to that alone.
 
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