One of the often overlooked segment of the cooling system is the coolant bypass hose. (Fig. 30, Item 14)
The Parts Manual does not provide a NSN for this hose, but it does specify the manufacturer number as 23500084 for the 6.2 and 6.5 NA.
On our 6.5 NA, the hose itself is marked as Gates 12555550.
We were unable to locate this part number under any cross-reference. The TM specifies the hose can be made from P/N 4377 at a 5″ length for the 6.2/6.5 NA. We were similarly unable to identify or cross-reference this part number.
As the TM indicates the hose is identical for the 6.2 and the 6.5 NA, we researched the hose for the 6.2 diesel and identified three GM part numbers: AC Delco 30124, AC Delco 30127 and GM 88909065. Each of these part numbers return as 5/8″ coolant hose.
Update: Regardless of the call-out in the TM and cross-reference, the hose on our 6.5 NA was 3/4″ not 5/8″.
We note that there are references found on the internet that people have unsuccessfully identified this as 3/4″ hose. These experiences indicate that the hose appears to fit, but leaks, and was subsequently identified that the application calls for 5/8″ hose instead of 3/4″ hose. As an upgrade, and to prevent future maintenance issues we have acquired 5/8″ silicone coolant hose. (in black, to maintain original appearances). We re-ordered 3/4″ black silicone coolant hose, as our 6.5 NA application requires 3/4″ not 5/8″ This hose is often used on agricultural and industrial applications and sometimes carries a higher pressure rating. (200 p.s.i. vs. 60 p.s.i.) Additionally, the jacketing on the silicone hoses seem to degrade slower than the EPDM hoses, and seem somewhat more resistant to abrasion. (foreign material being blown into the hose from the cooling fan).