When it comes to the 1955/56/57 Thunderbirds more than likely this subject has been discussed and written about more than any other. Even when new, during certain driving conditions (parades & city driving) coupled with excessive ambient temperature the Thunderbirds were prone to run toward the hot side of norm. One reason for higher than normal temperatures was in the design of the engine compartment not allowing air to escape and a basic design flaw in the water pump system. The engines were the same engines used in thousands of Ford passenger cars and trucks, but the passenger cars and trucks did not have the same tendency to overheat.
The water pump for the Thunderbirds was the same as used on passenger cars and trucks. The timing cover for both the passenger car and Thunderbird were similar in design both were built to accommodate the water pump. The cavity for the water pump impeller was approximately 5/8” deep. The water pump impeller was approximately ½” thick. This combination worked fine in the passenger cars and trucks. When the same engine was used in a Thunderbird it was necessary to install a 1&1/8”’ spacer between the water pump and mount cavity to accommodate belt alignments. When this spacer was installed the water pump impeller did not fill the extra cavity created by the water pump spacer. The results were a lesser volume of coolant being pumped through the engine. This lesser volume of coolant coupled with infrequent radiator flushes and coolant changes created an accumulation of rust in the rear cylinders of the block. A re-designed water pump spacer is now available, developed and tested by Chris Ames in Arizona it has proven to be very effective in controlling excessive engine heat. Read his article on the CTCI website at www.ctci.org click on CAR TECH, Gil’s Garage then Engines, then click on “Revisit 1955/56/57 Thunderbird Overheating” within that article click on “Eureka Moment with Engine Cooling”
The conditions mentioned in the second paragraphs of this article contribute to overheating especially during city driving or parades. This problem can sometime be overcome first by cleaning the block. The rust must be removed by breaking it loose and flushing it through the core plug holes. This can be done with the engine in the car, but best done with the engine removed. After the rust is removed a high volume water pump with an extended impeller can be installed, available from CASCO. In addition a thermostat with a larger opening can also be used. This combination has proven to be very effective without ill effect.
Other items that can contribute to a cooler running are as follows.
1-Head gaskets properly installed, square corner should be at the top in the front of the engine.
2-Install a six blade fix (nonflexible fan). The edge of the fan should be out of the shroud approximately ¼”.
3-Install a full lower radiator shroud.
4-Insure the timing is properly set throughout the full range of power. The 1955/56 must be set two places, initial and vacuum advance during acceleration. The 1957 model must be set three places, initial, centrifugal and vacuum during acceleration. The exact specifications can be found in the shop manual available for each year from CTCI.
5-When installing a new water pump check the clearance between the water pump housing and back side of the impeller for proper clearance (0.030-0.040). This information can be found in the shop manuals.
6-Insure the heat riser on the right hand exhaust manifold is working properly. It should operate freely by hand and open during acceleration. The counter weight goes down as it opens. Better yet replace the valve with dummy (flapper removed) or a spacer.
7-Install an electrical fan, especially if air conditioning is installed and the car is used in parades or extended slow city driving. I prefer a pusher mounted in front of the radiator between the air conducting condenser and radiator.
8- Insure the radiator hoses are in good condition and not spongy especially the lower house. The lower hose has an internal anti-collapse spring.
9- Radiator should be clean and have at least four rows of cooling tubes and 14 fins per inch. Heavy-duty radiators are available.
10- Coolant additive are available that claim to reduce boiling.
11- See page 386 & 387 of the restoration manual on how to relieve hot spots between 2 & 3 cylinders on the right bank and 6 & 7 cylinders on the left bank of the engine block.
All the parts mentioned in this article are available from major Thunderbird Parts dealers.
The most important items are a clean radiator, rust free block without build up around the internal water jackets and properly set timing throughout all power ranges.
The bottom line is after properly complying with all the recommendations and the engine still over heats it has rust build up or is a 312 with cylinders over bore of 0.080 or more.