would i be hurting a 2007 sonata V6 3.3 auto transmission by coasting in neutral at 25 mph or less for about half a mile at a time?

 

It's not the best thing for the trans because it's the input from the engine that pumps the fluid. However, coasting in neutral is illegal in most if not all states.

 

Why would you want to coast that much?

If it's because you believe you're saving fuel, think again. Many of today's engines shut the fuel deliver off during deceleration. You may likely be wasting fuel.

 

According to my Scan Gage, putting the car in neutral can make a huge difference. In my KIA, Spectra, coasting at 60 will show about 100 to 120mpg, put it in neutral and it goes up over 200 mpg. There are a couple of spots where I can coast for close to half a mile. Yes, that does make a difference at the end of the tank. I haven't tried it on my sonata. I also hadn't heard about it being at all damaging to the transmission. I just assumed that if the engine was running, the transmission was being lubed just fine. I reckon I got me some more learnin' to do.