1966-1970 Chevelle Oil Pans
There are three distinct 66-67 Chevelle oil pans. The first two have the front center hole (which is for a bolt that screws into the bottom of the timing cover, so you have to have the correct timing cover too). version 3 does not have that hole.
Version 1 of the pan is a 66-only pan. This pan was used on Chevelle 396 engines assembled through at least 12/30/65. It may have been used longer than that, and may have been used all year on 66s. All 1965 to 1967 Chevelle 396 oil pans have a bolt hole in the very front center of the 396 oil pan where a center bolt attaches the front center of the oil pan to the lower part of the timing cover.
In addition to the front center bolt hole, version 1 has a much simpler oil baffle design than versions 2 and 3. The baffle is completely flat with no "X" or "V" shaped impression in it. Version 1 also has less indentions on the sides of the pan than the later two versions (the indentions are there to hold the baffle in place for spot welding, and the simpler baffle required less indentions to hold the various pieces of the baffle in place). Version 1 takes a curved dipstick tube rather than the straight tube that was used in 67.
1965 to 1966 Chevelle oil pans have a 1/4” stamped indentation in the center of the oil pan about 4” from the deep part of the pan, but before the two tie rod indents.
The version 2 pan is identical to on 3, except that version 2 has the front center bolt hole like version 1. The version 2 pan is either a late 66 pan or an early 67 pan. It is uncertain when the front bolt was eliminated from production. Based on what has been reported, the extra bolt was eliminated either at the end of 66 production or shortly after 67 production started. If it was eliminated at the end of 66 production, then the version 2 pan would have to be a "late 66" pan. If the bolt was eliminated shortly after 67 production started, then version 2 pan is probably an "early 67" pan.
Note the differences in the sump area of the version 3 oil pan vs. the version 1 on 1966 396 engines.
The 1967 version 3 oil pan baffle, note the 'X' design.
The 1967 Chevelle oil pan has a 3/4" stamped indentation in the center of the oil pan about 4” from the deep part of the pan, but before the two tie rod indents.
1969 and later
1969 and later Chevelle oil pans moved the drain plug to the lowest part of the sump.
The baffle on later Chevelle oil pans also changed from an "X" pattern to a "V" (or "Y" if you like) pattern.
Full Size Chevrolet Oil Pan
Note these two pans are marked as 1966 Chevelle but are really full size Chevrolet oil pans and not from 1966. How can you tell? First there is no bolt hole in the front to bolt to the timing cover; second there are no tie rod indentations; third the oil drain plug is at the lowest part of the sump. So, be careful when buying an oil pan at a swap meet or salvage yard - don't go by what someone writes on the part.
Note tie rod indents required on Chevelle oil pans.