We get these questions on a daily basis in the warm months; "How do I keep my 6.5 cool?". "How do I stop my 6.5 from overheating?".
Over the years, there were multiple revisions to the cooling system, however, it's generally accepted that the 2000 model year system is the end-all solution when coupled with a Duramax composite fan blade. The 2000 model year pump addresses balanced-flow issues between the cylinder heads while having the highest flow rating to boot. It's required to use all three items together because all trucks before 1999.5+ had a 4 bolt fan clutch mounting hub. The 2000 has a spin-on fan clutch like most all current GM truck designs. Note, the Duramax fan clutch is not used because it has a higher engagement temp. Stick with the Hayden listed below for a better match.
The two water pumps shown are identical with the exception of one being OE quality, more expensive, and the second being aftermarket quality, cheaper
This video from our friend Daniel is great at showing you the water pump differences:
If you have a dual thermostat housing (factory on 1997+ trucks), we also carry a billet fabricated BRF (Bypass Restrictor Fitting) from Leroy Diesel. It is designed to promote additional flow through the cylinder heads when the thermostats are open:
Cleaning your cooling stack and factory radiator can go a long way also but it's frequently not enough. If your radiator is 20+ years old, then there's a lot of improvement to be had. The mechanical components above couple perfectly with our all aluminum radiator to complete the package and ensure you never have a cooling issue again:
The Duramax fan blade should clear your factory shroud fine, but trimming with a flapper wheel or dremel is sometimes required. The most common issue that would cause the fan to not fit would be worn or sagging factory rubber motor mounts. We highly suggest swapping in a set on Energy Suspension polyurethane mounts in all trucks due to their age and fact the replacements mounts available are not heavy duty enough for a diesel engine.