Hey you Great Gurus: Will Not reinstalling the 3 plastic 'Engine Covers' under the hood (for my future convenience, I'm the mechanic) possible decrease the efficiency of radiator cooling....due to some outside air flow bypassing it's flow through the radiator?

Inquiring minds want to know! ThanX in advance!

 

Nah. They just keep the dust away from the engine.
I haven't put the plastic cover on the engine in my IS300 since I did the timing belt last year.

 

I'd rather leave it off but then I don't have any space to put them in the garage.

 

They are for sound reduction. OK to leave 'em off.