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Old 05-07-2017, 06:33 AM
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Robyn Robyn is offline
Missy Good Wench ( Moderator)
Join Date: Apr 2001
Location: Newberg Oregon
Posts: 10,513

If you have a late block that was mfg by Navistar for AMG (Post GM ) then the following data is useful

The first two digits are the month, the next two digits are the day of the month, and the letter indicates the year in which it was cast. So, a "03 17 L" would be March 17, 2004.

H = 2001
J = 2002
K = 2003
L = 2004
M = 2005
N = 2006
P = 2007

As Maverick mentioned the date code (Julian date) is on the rear flange of the block just ahead of the bell housing surface right behind the RH head.

GM cast blocks are coded differently and the code usually begins with a letter.


Letter denotes the month
Two numbers are the day
Final numbers are the year... these can be a single digit

C-06-6 would be March 6th 1996

Being a 506 casting # makes it a 6.5

Another set of marks to look for to be sure who made the block (GM or Navistar...AMG)

A figure like this <> will be cast in the valley on the later blocks cast by Navistar for AMG.

There should also be an oil pressure port in the valley about mid way forward on the left side (looking from rear) as well as the oil pressure port behind the left head on the flange.

The blocks cast after 2000 If I remember correctly also saw the oil cooler ports go to 1/2" pipe thread from the earlier 3/8" pipe thread. (Ports on lower left side of block by the filter)
(1) 1995 Suburban 2500 4x4
(1) 1997 Astro
(1) 2007 Chevy Avalanche
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