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To Heat my intake or not? Subtitled: Running water from an engine to heat an intake a good idea? NO!




1st we should start about heating intakes, and to make it easy this is primarily about Chrysler/Dodge/Fargo/Desoto/Plymouth intakes on Flathead (L-Head) engines from the 1930s-1950s and I would also refer you to read my article on multiple carbs.


Chrysler Corporation was building cars and trucks to run 12 months a year and under conditions that range wildly in terms of how hot, how cold the climate was as well as different levels above sea level.    This is going

To be at a more high-level basis, because clearly a difference between Alaska or the Yukon in January which has been as low as minus 80Ff/62.2C and the average temperature in Florida in January, or even the coldest which was minus 2 degrees Fahrenheit. It was recorded at a Tallahassee station on Feb. 13, 1899      And of course summer time temperatures at either, or out in the desert.


Had Chrysler built engines to operate on nice spring, summer and fall days between 60F/15.5C and 80F/26.5C they would not have created intakes and exhaust setups that they did.  That is just a fact.  That is important because for most vehicle owners reading this, they have a nice car or truck that they primarily use it for 3 seasons and when it’s snowing out or over 100 degrees F it’s not the normal temperature, they are operating in.



What Chrysler did come up with for their 4 seasons, all weather engine setup was to bring the exhaust up close to the intake although actually put an asbestos based washer to place in between to provide slight separation of the two.  When the engine is cold or cool there is a flap in the exhaust cavity connected to the intake that is in an open position, allowing a heat to rise up under the intake where the carb is. That allows the intake to quickly warm up and help the engine at start up and with the engine “warms up”.  I could go into the scientific pieces behind that, but lets just leave it at that.


When the exhaust reaches a certain temperature there is a coil spring which the heat effects the spring and the flap moves from the open, to the closed position, thus lowering the amount of heat going directly to the intake. This actually happens relatively quickly under the temperature ranges I described earlier and even in temperatures well below that down to freezing, it still closes relatively quick and most certainly well before the engine’s water/antifreeze temperature reaches the point where a thermostat would open. This fact become important later on in this discussion.


It is very effective although 60-90 years after they came from the factory, they are often found with the coil spring gone or ceased up leaving that flap in some position between wide open and closed.  If it’s closed that actually is far better than wide open.


The reason being if it remains wide open after the engine is warmed up, gets into the 165-180f range continuing to toss a lot of heat at the intake will

Actually, change the fuel/air mixture and not for the better and when you turn off the vehicle and then restart it after just a few minutes you may encounter what is often referred to as “fuel percolating”


In winter condition and certainly in the far north in the winter, you may know or have heard of people putting cardboard or shutters in front of radiators and the reason they do that is to reduce the amount of air going through a rad and therefore slow down the cooling efficiency of the system. Even with this in place to try and bring the engine temperature up quicker and of course get it so the heater in the cab of the vehicle is working, that flap helping to warm up the intake shuts of fairly quickly.  That too will be important later on.


To add a little wrinkle into this discussion Chrysler actually created a factory dual intake and dual exhaust for big trucks, which often times were designed as winter plow trucks and they never had any such flaps that turn and off the exhaust heat under the intake.  What they did was use a different metal allow which had aluminum as the base element in an equalizer tube and intake which both drew heat during start up.


A side note here that many may not realize, the alloy the intakes were made of by Chrysler for single carb intakes changed with the metallurgy over, with things changing a great deal from preww2 and post WW2. One of the reasons was at higher elevations in the heat of the summer cast iron intakes can actually freeze up or frost up with a “refrigeration effect”.   That is something Chrysler lead the industry in, while GM/Chevrolet   had intakes decades later with this “freeze up” or frosting effect.    It is why in my opinion the leading reason why one of the big pushers of water heating intakes comes from the GM world and their experience is limited if any with Flathead Mopar intakes and operation.


Now let’s shift to the aftermarket arena and almost from the start, running multiple carbs to better balance fuel distribution and of course dual exhaust to better equalize back pressure.


A could time to suggest reading my piece on multiple carbs.   You will also see that - no, multiple carbs are not just for racing or super high performance.  You can increase fuel economy and make an engine for more efficient with multiple carbs/






So now that you hopefully have read about multiple carbs and realize while yes if you were building a race engine you would want multiple carbs but if you can afford the additional carbs just the pure increase in fuel efficiency makes the modification worthwhile.


Now let’s talk about the Elephant in the room, you have decided to run an aftermarket multiple carb intake.       Some in the past seemed to have water heating on the outside of the intakes, while other didn’t.    Edmunds had water heating and then dropped it in their late manifold for Mopar’s how come?


Then the later created manifolds (post 2000) don’t seem to have water heating, like the AoK intakes. Was that because they are just for racing?


The answer to that question is absolutely not, but clearly there is more to that that just No!


I will explain why shortly and no, it wasn’t because we forgot about heating the intake or because it would cost more.   If it had been the better thing to do, we would have done it in a New York minute!  In fact, we designed both our AoK intakes for both heating of the intake and utilizing some very high-tech metallurgy that actually helps with the both overheating and with things like the frosting or freezing situation that Chevys ran/run into.


Let’s start with the “really cold” outside and below 0F which of course water freezes are 32 F or 0C.  Now this isn’t in the range I described earlier but let’s start here.


You start up your car, likely need to use a choke to get the car to start and you have an aftermarket intake that doesn’t have a connection to the exhaust. What happens. Depending on how close the intake is to that exhaust, and what the intake is made from, there will be heat coming off the exhaust that will rise and provide heat on to the intake.  Interestingly with the exhaust running under all of the intake will provide an even distribution of heat where on the original single carb setup you get more heat hitting the middle but of course that is where the 1 carb sits.   On your multiple carb

Setup tossing the heat just to the middle of the intake isn’t as effective.


In the case of most of the aftermarket aluminum intakes, even the early ones they actually will warm up fairly quick.  Certainly, faster than cast iron.  The later intakes like the later generation Edmunds actually changed their aluminum mixture so that over the longer term the intake didn’t deteriorate and they actually found that mixture helped conduct heat from the exhaust quicker.


But back to its “really cold” and well wouldn’t having water/antifreeze going beside the intake help warm it up?


The temperature of the water/antifreeze (lets call liquid) is actually below freeze and only because off the magic of antifreeze or “colligative properties in action” that the water/antifreeze isn’t frozen.  We start up the engine and while we are getting heat coming from the exhaust warming up the intake, guess what, liquid being so cold actually draws heat from the intake.   Here is where the elephant has basically **** in the middle of the room.  Faster than your exhaust he can heat up the intake, the liquid is drawing heat away from the intake and worse when this liquid is just running along the outside, it becomes a “heat sync” changing the temperature on the outside of the intake compared to the inside of the intake.   Run that water on the underside and it becomes and even more efficient heat sync drawing more heat from the intake.


In fact, by the time the engines liquid temperature has reached a point where it might actually help warm the intake, the engine would already be warmed up and running well.    


Now let’s move to where the thermostat opens because the engine is 160F – 185F and you are still running the liquid to the outside of the intake and guess what, you are actually introducing more heat to the intake when it doesn’t need it. As well you still

have the added issue of your changing the part of the intake that has the “liquid” flowing by its vs the rest of the intake.  That has a negative impact on the air/fuel mixture so unless you have a way of shutting off the flowing of the liquid you have a problem when the engine is hot, a problem that is even worse when the outside temperature is summer time hot.


Even if you can figure out a way to shut of the flow of liquid going by the intake when it’s too cold or too hot which will be a big challenge, by the time the liquid is the temperature you were looking for to help heat the intake, the engine is already running well.


Now in the past, provided that information, the “unnamed GM engineering guy” eventually came back with – “the other reason you want hot water running by your intake is to stuff it from icing up in the summer”.


Well, if you’re running a GM with the cast iron intake, I’m not sure.  nor to be honest

do I care although the heating the intake with antifreeze/water in the cold concept, goes down the drain really quick because running cold liquid by, even a cast iron intake still has the heat sync issue?


For a factory intake or any of the aftermarket intakes I have seen the metallurgy is such and the proximity of the exhaust to the intake is such that there is no freeze up or frosting of the intake that we have ever seen.     Even at higher elevations where its more of a potential to be an issue I know of several guys running late generation Edmunds intakes and not having an issue.


On our AoK intakes we used modern metallurgy magic and introduced a lot of elements that were not used in the 30s, 40s, 50s, or even the 60s and 70s.  One of those is silicon. This modern alloy mixture actually helps both better utilize heat coming from the exhaust at start up, but actually repels heat when the intake reaches a certain temperature range and when it encounters conditions that will definitely see the GM ice up in the summer, the AoK intakes metallurgy makeup actually utilizes the constant exhaust heat and not only does frost up like a Chevy. lol. but actually, helps the fuel/air mix better because we have casted in end caps which promote swirl and the heat hitting the intake provides a stable environment for that to happen.   They are not flathead side valve engines with 3 ports feeding 6 intake ports but even modern intakes feeding overhead valve and overhead cam 4cylinder to v8 to v10 engines are not running water/antifreeze beside or through the intake, oh and even GM has changed the mixture of metals from the cast iron mixture they used long ago.



Now if you happen to have an old intake on your Mopar with a single carb on it, and you can’t turn the shaft that turns the flap or the spring steel is long gone and we have no idea whether the flap is open or closed, taking off the exhaust and closing off the gap would be a really good idea.    You can buy a phenolic washer to go between the intake and carb to help stop the “percolating effect” although blocking it off or welding it shut would be a better


Side topic – antifreeze and running it in an engine.



 Antifreeze is the perfect example of colligative properties in action.  Antifreeze is a mixture of water and ethylene glycol.  The ethylene glycol is the solute.  Cars typically have water in their engines to keep them cool, but if the weather outside gets below freezing, the water would freeze, expand, and crack the engine.  By using antifreeze, the freezing point is lowered and the cars are able to withstand a lower outside temperature before the engines are ruined. 



The purpose of antifreeze is to prevent a rigid enclosure from bursting due to expansion when water freezes. Water usually freezes at about 0˚C or 32˚F, but when antifreeze is added to it that changes to being able to freeze at about -50˚F. It actually takes a long time for the antifreeze to freeze.


Herein, can you freeze antifreeze?

The name “antifreeze” might trick you into thinking the coolant cannot freeze at all. But in actuality, pure antifreeze, which is ethylene glycol, will freeze between zero and minus five degrees Fahrenheit. Only by mixing antifreeze with water can you lower that freezing point.

Additionally, does antifreeze expand when frozen? Water is a pretty effective coolant, but if it freezes, it can expand enough to burst the rigid enclosure of an engine or electronic. To avoid icy explosions every time the temperature dips below freezing, we use antifreeze to change the water into a different chemical solution with a lower freezing point.

Additionally, what temp does coolant freeze?

There comes a point, however, where even antifreeze can't protect from a freeze. At -36 degrees Fahrenheit (that's -38 degrees Celsius), antifreeze and coolant will start to solidify, making it very difficult for your engine to turn over.



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