[Diesel_Dave]

The grille block should not affect the final operating temp--that should be determined by the thermostat. If the grille block is increasing the final operating temp, then it's too much.

There's basically 3 "stages" the engine potentially goes through:

Stage 1: Thermostat closed.
When the coolant temperature is below the "crack open temp" the termostat is closed and the coolant is not sent to the radiator at all. Usually the "crack open temp" is the temp a thermostat is know as--a "190 deg stat" starts to open at 190 deg F. In some cases, the thermostat is designed to let just a trickle through the thermostat to prevent air build up, but it's basically closed for all practical purposes. The coolant bypasses the radiator and goes right back to the block. In this stage, the coolant is getting warmed up by the engine and the only cooling that happens is due to the air passing through the engine compartent around the engine. This is how the grill block helps the engine warm up faster--less air through the engine compartment means less heat loss, so it warms up faster. The radiator doesn't really matter at this point because there's basically no coolant flowing through it.

Stage 2: Thermostat partially open. Once the temp gets to the crack open temp, the thermostat starts to open and some coolant gets sent to the radiator to be cooled. And some still gets recirulated to the block. The coolant that gets sent out to the radiator comes back to the block and (eventually) lowers the temp up by the termostat. This thus gives closed-loop feedback control--if the coolant temp goes up the thermostat opens more, which lowers the coolant temp, which cause the thermostat to closes more, which causes the coolant temp to rise again, etc. During this time, the coolant temp usually stays a ~10 deg F or so above the crack open temp. There will be some fluctuatin, but it should stay fairly steady. As long as your grille block hasn't over-deminished the cooling capability of the radiator, you should stay in stage 2 after the engine has warmed up. The temperature range should remain the same as it did without the grill block.

Stage 3: Thermostat completely open. This is the situation you want to avoid. If the coolant temp gets very hot, the thermostat has opened all the way, sending the max amount out the radiator--however, the coolant temp keeps going up. If the radiator doesn't have enough cooling capacity to cool the coolant, there's nothing to stop the coolant temp from continuing to rise. Many control modules are set to turn the fan on at this point--the purpose being to pull more air through the radiator and cool the coolant more. Either way, this is not good. If you see the collant temp continuing to rise above the normal range you've got too much grille block.


So, the benefit of the grille block is 1) slightly faster warm up times and 2) Less aerodynamic drag from less air flow through the engine compartment. The final operating temp of the engine should not be changed.