More than likely this question has been asked before but being new to this forum I have never seen it answered. When my 25 T is running the area of the intake manifold between the carb and the intake gets very cold. Even when the outside temp is in the 90s. Is this normal?
Yes, it's normal to some degree. The carburetor works by accelerating the incoming air so that it picks up fuel from the puddle of gasoline in the float bowl. Accelerating the air causes its temperature to drop. During humid conditions, things can get cold enough to cause ice to form.
Are you running a hot air pipe? It fits around the back of the exhaust manifold and runs down to the carburetor inlet, it will help by warming the air before it goes into the carburetor, see the attached pic.
Yes very normal. In Aviation we have a problem called carburetor icing. The temperature of ambient air drops maybe 30 degrees when the fuel rapidly vaporizes when mixed with in rushing air in the carburetor going to the intake manifolds of the engine. Ice can rapidly build up (say around 50 degrees outside air Temp) and high moisture completely clogging the intake with ice, and your engine stumbles and can die. We have a lever where hot air is added to the intake called "carb heat" to prevent this. This is the same principal Ford uses
As alluded to above, it has two contributing causes. Lowering the pressure of any gas (Air in this case) will result in a decrease in its temperature. When the cross sectional area of the flow is reduced (Like a carburetor venturi), the flow will speed up and the pressure is reduced (So says Mr. Bernouli). This reduction in pressure causes a reduction in temperature. Also the evaporation of a liquid (Gasoline in this case) requires some form of heat. It gets the heat from the surrounding air, therefore lowering the temperature of the air.
Here is a past threat with a bunch of information on why and what effect it can have:
Lucky for you, your model T shouldn't fall out of the sky if your carb gets a little ice on the outside.
Actually cold air gives more horsepowers since you'll get more oxygen into the engine for the same volume, so the carb heater is best used only when absolutely needed - that's at certain times in certain geographical areas when humidity and temperature in combination can give ice on the inside of the carburator too.
We used to pay for small bottles of ethanol to pour in the gasoline wintertime here in Sweden to avoid this type of problem plus to dissolve any water in the tank back before gasohol
Your going to have to explain this to me. I've heard of using ethanol as a gas-line antifreeze and water remover but how would it make any difference with carb icing?
The ice formed in carb icing is from the moisture in the air and not from moisture in the gasoline. Any ethanol in the gasoline would tend to increase any water mixed in with the gasoline and if anything make carb icing worse.
Water has a vaporization point of 212 degrees.
Ethyl alcohol vaporizes at 172 degrees.
Gasoline vaporizes from 100-400 degrees (due to octane, additives, etc) On youtube I saw a crazy man boil gasoline at 160 degrees.
Looking at the numbers above one could surmise that gasohol will boil at a higher temp than plain gasoline, but not by much, because the alcohol raises the vaporization point of the mixture.
Based on that observation it will take more energy to bring gasohol to its vaporization point(boiling point) than pure gasoline. IF it takes more energy, then it will lower the temp of the air around the intake manifold faster than pure gasoline.
i.e. One would expect carburetor icing to occur sooner with gasohol since it requires more heat to vaporize and cools off the intake manifold faster.
Any engineers or chemists out there can correct me if I am wrong.
The reduction is temperature is mostly caused by the change in pressure and not the evaporation of the gas. The air changes from atmospheric pressure to something less then atmospheric pressure past the carburetor/venturi. The greater the pressure change, the greater the temperature change.
It you run your T at full throttle you would likely never have a problem with icing because the pressure drop in the carb is less. At the same time you are using more gas.
If you running at a lower speed or maybe descending a long hill with the throttle nearly closed, then there is a much greater pressure drop across the carb, the temperature drop will be more and there will be a better chance of ice forming. That is why the chart show more danger in descent power.
That is true. The lower air pressure causes the temp to drop and the water vapor to condense out. But the heat of vaporization of the fuel also causes a drop in temperature.
How much each of the above contributes is up to Ford engineers to determine.
Interesting that there is an Onalaska in Washington and one in Wisconsin, too.
There is also an Onalaska, Texas. All three were named by the same guy, William Carlisle of the Carlisle Lumber Company.
Having been a pilot of light aircraft for 40 years carburetor iceing can occur at any rpm if the humidity is correct. An aircraft can be flying at a given altitude for several hours at full operating temperature at 2200 - 2300 rpm and fly in to a condition of high humidity ie through a cloud or fog and the carb can ice up severely enough to cause an engine failure. It is important to recognise the pending condition and apply carb heat prior to the condition. If the carb heat is applied too late it may not overcome the condition. Prior to every flight a cup fuel is drained from all the low spots in the fuel system to remove any water accumulation. The water naturally accumulates from the air that displaces the fuel, however this may not occur in Arizona but on the west coast with a marine climate this procedure is a must. Some years ago pilots were putting methylhydrate in the fuel tanks to absorb any accumulations of water, however the amount that was put in the fuel tank 8-10 oz did not have any effect on the water accumulations but caused sensitive aluminum carburetor parts to corrode thus damaging the carburetors. The MOT/DOT prohibited any further use of mehylhydrate in fuel tanks of aircraft. It was determined that it would take nearly the same amount of gasoline that was in the tank to absorb said water. The use of methylhydrate remains currently prohibited. A secondary note, gasoline vaporizes at -30, also the higher the octane reduces the occurrence of carb ice forming. Premium gas in a "T" will reduce its forming. It will not outright prevent it but will reduce it somewhat. There is no relationship between the water in the tank and the ice forming in the venturi. I was driving a Volkswagen at highway speed for 2 hours and encountered a severe wet snow storm and the carb iced up to a point I had to stop and let the engine idle to melt the ice before proceding. FYI DAVE