is the duramax motor fan from a 2003 chevy bigger or smaller than a 2006 chevy ,would it make any differcne if we put a smaller fan on the 2006 from a 2003 ,please help

all duramaxes are 6.6 liter or 403 cubic inch.... there are different engine designations.... LB7, LLY, LBZ, LMM..... but displacement is the same.

as far as using a smaller fan.... all depends on your environment and what the vehicle is going to be used for.

reason i ask is that the 2003 fan are smaller than the 2006 and i got a fan from a 2003 in my hands and are a bit smaller

Smaller diameter will give less CFM. With a 03 making 310 hp it worked now you are going to put that same fan on a motor making 360 hp. At 50 hp more there may not be enough CFM to keep it cool. IIRC the 06/07 fans are rated at around 15,000 CFM. CFM ratings are based on diameter, pitch angle of the the blades, and the number of blades. just remember the more hp you have, you need more CFM to keep it cool, even with the exact same size radiator.

It you tow over 10K then you might overheat with the smaller fan. The llys used the smaller one and had some over heating issue over 10K. The fan and some additional mods where done to keep the 06+ from overheating.

With a 03 making 310 hp

Those were rated at 300/520. They didnt jump until 04.5 with the LLY at 310/590 and 310/605. Not to nit pick or anything but you're right about the fan and the CFM moving so much more or less air.