Below is the grill block I made for my 03 Matrix. Its works very well. The engine warms up much faster and it also warms up the intake air to a small degree (3-8°F). However, since it is made of foam board it didn't hold up all that great over winter (its still there, just not as pretty). I don't drive the car a ton, but I did notice that this was a bit much for city driving, even in winter. I could hear the radiator fan kicking on and off quite a bit during the city driving. During highway driving its rock solid at 184-186°F. I have since removed the bottom block now that it is getting warmer out.
FYI, according to my Matrix service manual the radiator fan kicks in at 199°F.
