I drive a lot for work in stop and go on the freeway and on surface streets.
It probably won't help you. Grille blocking helps in two ways: By increasing air temperature under the hood (and therefore increasing intake air temperature), and by reducing aerodynamic drag at the grille. It's already hot enough where you live, and the type of driving you describe isn't heavily affected by aerodynamic improvement.
Thanks for all the information. I am not sure how I will proceed with this for now. I do drive on I-10 for 30 miles on the way to work and home. Depending on when I get my lazy rear out of bed I can beat traffic and cruise to work at 65mph or sleep in and go 20mph for 5-7 miles of the trip. I also drive to Tucson (120miles), Yuma (160miles) and Flagstaff(150 miles) on a regular basis. So if I can overcome the heat issue I do think the the aero mod will be worth the effort.
I was looking at the car some tonight and it looks like most of the air for the radiator on the scion comes from the lower grilles, there are three openings. So partially blocking the top one and possible the bottom one should be ok and still get plenty of air to the radiator.
I am going to get a ScanGauge before I do anything to monitor the temps while I am driving to see create a baseline to work from. Also this will help me see if there is anything in my driving 'style' that is hurting me.
Again thanks for all the info, I will post what I do in the future.
I spent some time today under the hood of the scion replacing the air filter and spark plugs. I noticed that they upper 'grille' on the scion is actually blocked. The grille goes no where. The two lower ones are where the radiator is. I also looked at the lowers and think that I could block about 1/3 of each and still get plenty of air to the radiator.
Here is what the grille looks like stock. (yes I am missing a piece in the lower part)
And this is what I could block and not affect any of the radiator access.
From there I will start to slowly block more grille and see how it affects temps.
I am also thinking about a way to make the upper grille smooth, not sure if that would help with aerodynamics but I think it would look better. I also want to get ride of the dB badge that someone put on the grille instead of the xB one that belongs there.
I have been looking at the same thing recently. If you look carefully the radiator is about 1/2 the lower grille width (or less) and offset to one side. So *in theory* you could block a fair amount before it actually affected air into the radiator significantly.
Also while you're looking you may want to see if there are any other holes in the radiator core support that is allowing air to get into the engine compartment without passing through the radiator. If so this is just wasted air that could be cooling your engine. Block up those holes for a (probably small) cooling improvement.
Lastly you could build ducting like was said above to force the air from the grille to pass directly into the radiator without just generally blowing around behind the bumper.
I say cover the middle first, and work your way outwards.
It is more aerodynamic in the middle than direct air towards the wheels and to the sides. It will provide more cooling than letting air in through the middle because there are hood latches and most likely vertical beams connecting the frame and engine cradle right there.
Anyway, here in Fort Worth in 100% city driving at around 96-98F my engine temps have not gone up at all... IT's all good 99% of radiators are oversized anyway.