Exhaust Question (Page 1/1)
1TrueJeff MAR 25, 10:34 AM
Hello! It's me again. I have an '85 Iron Duke SE, and I have a question regarding a tube/probably supposed to be a hose that goes from my exhaust to the air intake. How important is that? On mine its one of those tubes that you might see on the backside of a dryer, with the spiraling wire and the slivery surface. Its not secured at all, and is just pulled over the exhaust portion on the cat, and then the metal wire is holding it just firmly enough to hold it up against the air intake portion. Do I even need that? I like in Oklahoma, we don't have inspections or emissions rules or anything like that, you can drive 20% of a car here and its totally fine. Obviously if I didn't need that hose I should at least plug the hole in the cat so there no chance of water getting in, but I wanted to make sure that's not that important before I just cap it off and be done with it.
olejoedad MAR 25, 12:24 PM
That tube is to prewarm the air to the throttle body for cold weather driveability, and gets the warmth from the heat shield around the catalytic converter.
1TrueJeff MAR 25, 01:15 PM
So it is supposed to be that material? Should I put some hose clamps on it to hold them on then?
theogre MAR 25, 05:47 PM
⚠️ Warning: Thermac tubes may contain things are bad for you.
Wash hands and don't breath dust comes off/out of them.

Yes... a lot of cars even w/ EFI known as Thermac system to preheat air intake.
Is mainly to prevent Ice in the Carb, TBI, etc.

Big Tube is only part of system. Also have a vac line to a "switch" then to a "motor" that opens/closes a door in the air cleaner.

Other engines have heater loop of coolant system going to TB for same reason like V6 used by Fiero and others.
You L4 have coolant going thru intake. See my Cave, Heater

If you need hose clamp(s), only barely tighten just to seal and stay in one spot.

------------------
Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave

FranklinTurl MAR 25, 08:06 PM
I actually just got done replacing my exhaust manifold and I had the same question. from what I've gathered, it is not necessarily needed. I don't have one on my '84 SE and it seems to run super good without it! I tried looking for one to put on but couldn't really find it anywhere (although I didn't look that hard). It is used to bring warm up up to the throttle body for colder temperatures.
Blacktree MAR 25, 11:49 PM
As mentioned above, it's part of the thermac system. It uses heat from the exhaust to help warm up the engine on cold days. If you look on the air cleaner box, there's a thing on top that resembles a hockey puck. It should have a vacuum line attached to it. That "hockey puck" is the actuator for the thermac valve. You can test the actuator with a vacuum source (like a mity-vac). See if it works, before putting any effort into fixing the hose.

Edit to add: Yeah, the thermac hose was originally made of that aluminum "dryer duct" material. I can't remember if it originally had any hose clamps. But if it needs clamps to stay in place, then I would use them.

[This message has been edited by Blacktree (edited 03-25-2022).]

theogre MAR 26, 12:01 AM
Is often luck if a car w/ Thermac doesn't have "Carb Freezing."

I had it on a mini van and would freeze at "Random" times w/o the system working.
High Humility on cool days was worse and freeze while driving w/o warning.

Freezing can stall the engine, jam the throttle, and more.

New E-manifolds for Duke have the stove on them.
Likely are still heat tubes available thru various sources. Is often a generic part and won't list cars they fit. Just measure outer diam of port on air cleaner. Most are flex metal tube sim to use on clothes driers.

Side Note: Many Building/Fire Codes no longer allow Plastic outlet tube/hoses. Many do not "Grandfather" them too and fail if Inspected.
Because Plastic holds a lot of dust and plugs up causing problems and fires.