Good Day!

Why are dual thermostats part of the cooling mods?

If memory serves, the cooling upgrade GM introduced to our beloved 6.5TD in 97 (?) includes a higher-output water pump (85 (?) gpm to 130 gpm) & a new, dual thermostat housing. These components are fortunately available for retrofit from several top-quality DP advertisers.

Again from memory, this upgrade increased flow through the block ~ 75%, & flow through the radiator ~ 9%. This makes sense, as some of the cylinders (6 & 8?) seem to fail from overheat before any others; it seems like increasing coolant flow through the block might stop this problem.

My question comes up because if flow through the radiator is only increased ~ 9%, why do we need dual thermostats?

TIA & Blessings!