I just installed a cheap holder from Amazon, though I don't have plates from DMV yet.
It blocks a small portion of the grill, but it won't cause any overheating problems, I'm confident. Cooling systems are always over-engineered to account for the guy pulling a 3,000 lb trailer up a hill at 80 MPH in Death Valley.
I'm skeptical about it holding up in a car wash, as it's made of the flimsiest metal. I'll probably either take it to a touchless wash, or hand wash... I really only wash a car about once a year anyhow. Frequent rain here means cars aren't ever clean, but they also aren't that dirty.
Amazon.com