Wow 15 degrees? What are you using to measure (what brand or type of gauge) - I assume this was a water temp gauge - also did the stock temp needle move down at all too?
I am very interested in anything that can get me down even 10 degrees in my B13. I already flushed the radiator for the upcoming season and got rid of the Tsuru grille (everyone says they block some airflow) - run only distilled water and 1 bottle of Redline water wetter, added a brand new fan (old pass one was being tempermental) - new thermostat, new upper and lower hoses and clamps, no A/C and run ONLY the heat on settings 2-3 usually with the intake setting from the engine, and I still tend to towards the warm side when it's above 80 degrees. Where did you get the hood, or did you make it?
Oh and since this is the "what did you do to your B13" thread, I changed my switch from red to blue, most things in my interior are blue including the CD player and the gauge cluster so red didn't make sense.
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BTW- for those of you who are attentive to detail, YES that is in fact a HVAC from a 1992 G20 in my B13 SE-R