The casting code on a water pump is simple to decode. It includes the month, day and year such as J257. This decodes to October 25, 1967. Month codes are A through L for January through December. Beginning in 1970, big block water pumps used a two-digit year code to identify the year such as B12●72 would be February 12, 1972.
|V8 Water Pump Casting Month Codes|
|A - January||B - February||C - March||D - April|
|E - May||F - June||G - July||H - August|
|I - September||J - October||K - November||L - December|
Two basic styles of water pumps were used in V-8 Chevelles from 1964 to 1972. Naturally, the small block engine (283/307/327/350) and the big block engine (396/402/454) used different pumps but both used short and long styles. The 'short pump' was used from 1964 through 1968 and the 'long pump' from 1969 through 1972. Not only did casting numbers change but designs changed to accommodate accessory brackets.
The following list may not be 100% complete due to difficulty in researching an item such as a water pump that has probably been changed numerous times over the car's lifespan.
|283 195hp/220hp - 327 250hp/300hp
283 195hp/200hp - 327 275hp
283 195hp - 327 275hp
307 200hp - 327 275hp/350hp
|3953692||1969||307 200hp - 350 250hp, 255hp, 300hp|
396 325hp, 360hp, 375hp
396 325hp, 350hp, 375hp
396 325hp, 350hp, 375hp
|3931065||1969||396 325hp, 350hp, 375hp|
|3931065||1970 (early)||402/454 (All)|
|3969811 *||1970 (late) - 1971||402/454 (All)|
Depending on whose measurements you believe, you can still see the differences between the short and long water pumps in the photos below. Also remember that all small block water pumps and all big block water pumps will physically bolt up to their respective engines and will work quite well assuming the associated brackets (A/C, P/S, Alt., etc.) are used. Depending on the size of your hand you should be able to put your fingers easily between the back of the water pump and the timing cover on a long water pump but not a short water pump.
Small block 'short' water pump
Big block 'short' water pump
Small block 'long' water pump
Big Block 'long' water pump
Casting number 3856284 and date C 31 5 - March 31, 1965
Casting number 3856284 and date K 1 6 - November 1, 1966
Casting number 3856284 and date H 17 7 - August 17, 1967
* Casting number 3969811 and date K 11 9 - November 11, 1969 (found on December 1970 LS5).
Casting number 3969811 and date I 1 71 - September 1, 1971
Casting number 6263707 and date I041-1 believe to be September 04, 1971; extra -1 is unknown.
Another 6263707 1972 water pump. Note the date format is different - A5●72 for January 5, 1972.