You already know that mid-summer is not the time to aerate. To answer your question, lawns can be aerated in summer (golf cousrses do it and I have done it when the lawn was not stressed), but the lawn must be heavily watered thereafter to prevent adverse effects of the aeration. Although aeration will reduce thatch by removing it as the plugs are pulled, to be effective you are going to need no less (bare min.) than 20 holes per square foot. Rental machines make 6-9 holes per sq ft per pass.That's at least 3 passes min. Your problem may not be compaction. Are you aware that thatch impedes root depth growth? If your thatch is as bad as you describe, your time may be better spent using a power rake rather than aerating. But dethatching is even more agressive than aerating and should only be done when turf grass is in growth mode in the Spring or Fall.

What kind of grass do you have?
How often do you water and for how long?
How high/low do you mow?
When were the last two times you fertilized and what did you use?

Hey thanks guys, after looking into it more and the hot weather picking up a bit I'm going to do what I can to put it off till later Sept.

If you'll answer the questions, maybe we can save you a lot of hassle. Core aerating has some issues you should be aware of, but it depends on soil type and the other answers.

I forgot to ask if you have a sand soil.