Cooling System Function and Operation part 3
Intake Manifolds-Carburetor Spacers-Heaters
Intake Manifolds
Ford intakes are predominately cast iron, the only exceptions were special high performance engines. These include Shelby 289,302,351, 428, Galaxie 390-406 2X3, 427 all, 428 PI, and Boss 302/429. This discussion will deal with the intake role in the engine cooling system.
Coolant circulated through the block exits the block at the rear flowing upward into the cylinder heads, then is directed forward to the intake manifold cross over passage, towards the thermostat. The cross over passage acts as an equalizer of flow volume, permitting each cylinder head to move like amounts of coolant to the thermostat. Stock intake manifolds are dry except for this cross over passage at the front, no coolant circulates at the rear of the intake.
Many intake gaskets from the same family of engines will not interchange, installing the wrong gasket will earn you a not so nice coolant leak. Intake gaskets are interchangeable from one side to the other, this was not always so. Gaskets for Ford engines have a slot running around the coolant opening in the head at both ends. This feature permits coolant to escape externally instead of leaking into the crankcase should a leak develop.
Heads machined excessively on the deck surface loose the dimensional capability to seal with the intake manifold. Some have tried using two gaskets to compensate for errors here, this seldom works.
Many modern silicon sealers are available that claim they totally replace the need for gaskets. Most new car manufacturers tried these a few years ago and found them unreliable. Silicon sealers sometimes work well with gaskets, but some gasket makers warn against using them with their product. Excessive use of sealer creates a problem of its own. As it is compressed the excess sealer will protrude into the coolant passage, eventually pulling loose and flowing along with the coolant until lodged in a tight place like the radiator tubes, heater core, or heater control valve. Restrictions come in many forms, reducing cooling efficiency, silicone sealer is one, use it sparingly.
Carburetor Spacer Plates
Along with the exhaust heat passage running through the intake manifold to warm the carburetor on cold start up, many Ford engines used a carburetor heater plate. Carburetor heater is not exactly a description of this parts full function. It cools the carburetor more than heats it.
The carburetor heater plate has engine temperature coolant flowing through its hollow body. Hot coolant from the intake water passage near the thermostat housing is directed through the heater plate to the heater core then returned to the water pump return fitting. Many of you have removed this plate thinking that by removing the 165* coolant from the carburetor base it will perform better. The truth is that the 165* is quit cool compared to 350* intake manifold temperatures. You can see that the carburetor heater plate has an important function in cooling also. Visualize the exhaust cross over passage running through the intake manifold directly under the carburetor. Even after the heat riser in the exhaust system has opened super hot gases of many hundred of degrees are heating the intake, conducting this heat to the carburetor body. If you doubt the amount of heat present, look at the original 428 PI intakes, in most every case the bottoms are burnt through or has had a weld repair. High heat and fuel in the carburetor do not coexist well, fuel percolates flooding over into the manifold, causing hard starting and poor performance. The carburetor heater plate has a real function on street engines.
Many Ford engines of the 60's also routed intake manifold coolant through a heater hose that clamped to the carburetor choke housing. Its purpose was to heat the choke housing, aiding quicker opening of the choke plate after cold start up. Warm coolant will be circulating to the heater core and chock housing long before the thermostat is opened. When Ford went to the open air cleaner assembly on the 260 sprint and 289 HiPo, these engines did not have exhaust manifold heat ducts to supply warm air for the carburetor. It was found that on cold start carburetor icing was the cause of stalling and rough idle. The carburetor heater plate helped solve this problem.
Heaters
The passenger compartment heater is a part of the cooling system, coolant is being circulated as needed for comfort. Hot coolant (thermostat rating) is picked up in the area adjacent to the thermostat and pushed through the heater core where the fan removes the heat from the core in the same fashion that the engine fan removes heat from the radiator. Once the heat has been exchanged into the passenger compartment, the coolant returns to the engine through the water pump return fitting.
Many cars experiencing over heating problems can show a dramatic temperature drop by turning on the heater. Understanding this occurrence you need to know two things, first you are increasing the effective size of the radiator by the amount of coolant cooled by the heater, second you may also be using the heater fan to make up for poor air flow through the radiator.
Most cars with factory air conditioning use a heater control valve to shut off coolant flow when a/c is selected. This keeps hot coolant out of the heater box, allowing quicker cool down after the a/c is turned on. Fairlane heaters (non a/c) have coolant flowing through them constantly. To control the comfort level inside the car, blend doors within the heater box are open, closed, or at setting in between these two, restricting air flow over the heater core.
Fairlane heaters (non a/c) have coolant flowing through them constantly. To control the comfort level inside the car, blend doors within the heater box are open, closed, or at setting in between these two, restricting air flow over the heater core. Cars with a/c usually keep hot coolant out of the heater box completely. Using either a manual (cable) or vacuum operated heater control valve to block flow. This design makes heater boxes simpler to build, not having to segregate the heater core from the evaporator.
Passages in the heater core are very narrow compared to the amount of coolant that flows through them and are susceptible to becoming plugged. Clogging of the heater core is one reason for flushing the cooling system.
Caution should be used when back flushing the system, the heater core needs to be segregated in order not to clog it with debris. You may not find this out until cold weather when no heat is available. Many auto repair shops use ineffective methods of servicing a coolant system. Most of these methods would be better described as a drain and fill, rather than a flush and fill. Improper knowledge of flushing can cause more harm than good. Later in this series I will go into detail about proper steps for flushing, why they are done, and consequences of poor workmanship.
Heater cores are quit ridged and very strong, capable of withstanding considerable pressure. In the early 60's Ford found many heater core failures due to expansion, this condition was most prevalent in high performance cars with low rear gearing. The efficiency of the water pump at greater rpm's was moving volumes of coolant through the heater and forcing it apart. Ford's fix was to put a restriction in the elbow fitting coming out of the intake supplying the heater. This restriction reduced the opening down to 1/4" on the hipo cars. Two things should be noted at this point; #1 stock water pumps need not be replaced for high performance street use, they are capable of moving far more coolant than most cooling systems require. #2 If you turn high rpm's and still have a heater in your car, find a way to restrict or close it off.
Many cars experiencing over heating problems can show a dramatic temperature drop by turning on the heater. Understanding this occurrence you need to know two things, first you are increasing the effective size of the radiator by the amount of coolant cooled by the heater, second you may also be using the heater fan to make up for poor air flow through the radiator.
Next time we will discus: Thermostats, Thermostat Housings, and Water Pump by- pass Hose.
Mike the Radiator Man