frost on intake manifold

D

Dick Webber

Senior Member
My friends took out their 1924 touring today for a New Years Day run. It ran great, but develops lots of frost on the intake manifold. Does not affect running. Temperature was about 50 in Kentucky today, partly cloudy. The touring has recently been awakened from a 25 year sleep.

What causes this?

Thanks,

Dick
 
A hot air tube works good and add some Marvel Mystery oil to the gas every fill up.
My speedsters will actually freeze up and cause the engine to spit etc. Marvel fixed the issue.
 
Dick Webber said:
My friends took out their 1924 touring today for a New Years Day run. It ran great, but develops lots of frost on the intake manifold. Does not affect running. Temperature was about 50 in Kentucky today, partly cloudy. The touring has recently been awakened from a 25 year sleep.

What causes this?

Thanks,

Dick
Click to expand...
The transformation of a liquid into a vapor requires heat. When your sweat evaporates it absorbs heat from your skin. When gasoline is vaporized in a carb, it absorbs heats and lowers the temperature of the intake manifold. The temperature drop is about 30 to 35 degrees. On a humid day, moisture in the air will condense on the intake manifold and and freeze. The same thing can take place in your carb under similar conditions. Airplane pilots call it carb ice. In motors where the throttle plate remains at the same setting for long periods of time, ice can actually cause the engine to gradually loose power and shut down. Flying over the carolinas one muggy day twenty years ago, the Citabria I was ferrying to FLA quit several times as the plane had sat for several years and the carb heat was not operating properly. The last time it quit, I glided into a landing at Grand Strand and was surprized when the motor suddenly went to ful power as I was rolling out. The prop had been windmilling as I descended with the throttle wide open and when the carb ice melted, it roared back to life!
 
Why would that hot air pipe have no way to keep the hot out of the carb till needed? The hot air reduces performance.
 
My NH on my speedster with out hot air pipe would condense moisture on carb body. Even on 70-80 degree days it would show signs of the carb and intake being DRASTICLY cooler than ambient. The icing will hamper performance more than heat.Ever looked into smoky unicks hot vapor experiments back in the 80's?I saw one on a fiero once.Interesting.Much like the vaporiser setups therory.
 
I fought freeze-up on an old 1930 Farmall Regular when I ran it on hot humid days in the summer time. Paul from Maine's explanation makes a lot of sense to me. It sounds like the way I was taught refridgeration works. Something to do with pushing a gas through a venturi, And the evaporation dropping the temp and causing it to almost supercool. I know the tractor collectors, of which I was a mere novice, told me to put a piece of tin from the manifold down over the carburetor. I never put the tin over the carb because I didn't want to "ugly up" my tractor. But now 20 years later it makes sense. I thought, and believe me I'm gettin' old and losing my memory, but I thought they called what was happening a "vapor lock", and that my carb was set too lean. At the time I recall I messed with that carb a lot and never got rid of the icing up. Now everything is making sense to me and the stars in the galaxy seem to have found their proper place. Thank you Paul from Maine. I think this whole thing might explain why all my kids were born naked.
 
Here in sunny Fla, without the heat pipe my '17 with an NH actually forms an ice plug in the carb and dies on the spot. Have had it happen at 90 degrees and sopping wet humidity. With the (factory) heat pipe, no problems and performance is fine.

T's from '19 through '26 usually had a hot air pipe installed at the factory. I think it was/is part number 4582A and is available from most of the T suppliers like Lang's. Cost about 14 bucks.

If you look on the Model T Club of America forum there is a ton of discussion about this subject. Most if not all the experts on that forum contend that the heat pipe is not needed with modern fuels. The consensus there is it was only required for the 'antique' low octane gas of those days.

Not one to argue with experts but after 36 years of building and driving T's I'll just leave the 'ol heat pipe where Henry put it.
 
I would suspect that modern fuels have more of an icing effect than fuel back then because of the ethanol content. Alcohol has a much higher "latent heat of vaporization" than gasoline (it takes a lot more heat to vaporize, and it has to be in vapor form to burn). The octane rating of the fuel has nothing to do with icing (unless, of course, octane is increased by adding more ethanol).
 
Mine has never quit or run real bad. I have checked the plugs and they always look the same as a hot day. I did add bigger jets when I 1st set this carb and intake up. It's been on my car for six years now. I drive my car all year around. I took it work the other day and the cold morning air was 28 deg.
 

Attachments

  • cold intake.jpg
    cold intake.jpg
    69.2 KB · Views: 35
As far as I know all Model T's came with a hot air pipe. Even today's cars have a hot air pipe that takes warm air from around the exhaust manifold to the air cleaner. After the Model T the A's had a hot plate that put the intake in contact with the exhaust manifold. Even with today's fuel my T wants to frost up without the hot air pipe.
 
Too add to this. It's not how cold the air is but how much moisture is in the air. You might have more moisture at say 50-60 then in the 20's.
It is not the alcohol in the fuel it is the moisture the causes the frosting. The problem has been around long before alcohol has been added to the fuel.
 
You must log in or register to reply here.
Back
Top