More on Ford flathead overheating

September 1, 2008 | By Richard Prince


This letter is a response to the January 2008 questions about the Ford/Mercury flathead overheating problem.

There are two basic flaws in V-8 flathead design. The first is the casting of the block and the second is the design of the water pump.

When the first flathead V-8 was introduced in 1932, the block was sand cast and it remained so until 1953. Ford was never able to clear all of the sand out of the water jackets. After a period of time these sand deposits would solidify and restrict normal water flow. This would contribute to an overheating problem.

The water pumps were on each side of the block and were propelled by the fan belt. The early water pumps were of a bushing type and later models employed bearings. When pushing water through

the pumps it went through the water jackets so fast that the water recirculating through the block never had a chance to cool down.

I learned a trick from an old race car driver. What he did was remove every other fin on the impeller, slowing down the flow of water.

I’ve done this and it works.


There is some disagreement concerning the effect of increased water pump flow on V-8 Flathead cooling. Beginning in 1949, Ford redesigned the water pumps to flow approximately 75 gallons per minute at 4000 engine rpm, which is about 25% more coolant than the earlier pumps could move. The updated pumps had eight vanes in place of the earlier design pump’s six vanes. The new vanes also had a more efficient shape that enabled them to propel more coolant forward. Some respected Flathead specialists believe that the second design pumps enhance cooling capacity by virtue of the added coolant flow rate. The additional coolant pressure that results is also thought to reduce the likelihood of vapor bubbles, which lead to hot spots and the propensity to overheat. The later pumps can normally be used on earlier engines but the modified impellers have to be trimmed to eliminate an interference problem. Also, the bypass hole on the top of the newer style pump has to be plugged when it is fitted to a pre-1949 engine.