Hood Vent

[f5fstop]

Only way to find out if you have any hot spots under the hood is to monitor the under hood temps at various points. You can have a 50 degree variance from the front to the back of an engine compartment and not know of the variance.
This 50 degree difference will not show up in the coolant, except as a small movement of the needle.
There are two vehicles on the road right now that I know have large variances in under hood temps, and it is causing problems with their engines. The problems appear at around 50K and can be serious. Engines are both V6's and are aluminum, and are NOT made by GM.
Jeep wranglers are notorious for having large variances in under hood temps from one area to another, that is why many who offroad in a desert install vents.
I agree with sledgehammer, unless needed there is not requirement for a real vent. In addition, as sledgehammer noted, adding the vent would require vents on the side (or rear of engine compartment somewhere) to allow the air to flow through.