How hot is "HOT" on a transmission fluid (ATF) dip stick?

Question

I want to add some fluid additive (Lucas) to my transmission, but I don't want to overfill it. The dipstick has add, warm, and hot for measuring. So how hot is the hot level? My temperature gauge only gets up one third of the way going 70 on the freeway, and the fluid only gets up around the bottom of "HOT". Can I safely add more fluid in that range (less than a quart)?

Edit: For the record, this vehicle is a 2000 Dodge Neon. As jmort indicated, I filled everything up over time and the level didn't really go up too much (maybe 1/4 or so of the way up on the HOT portion of the dipstick -- the bottle was 24 oz).

Answer 1

You can add more fluid, but it's best to do it slowly. Your transmission has a lot of gears and tunnels and holes for transmission fluid to go, and it's important to get the fluid down in there in order to get an accurate reading on the dipstick.

After adding fluid, take another ride out on the freeway for a few minutes and make sure you go through all of the gears. When you come back, park on a level surface, keep the motor running, and check the fluid again. Be extra careful you don't overfill it.

Answer 2

Hot is when the transmission and engine is fully up to temperature. So, 15 minutes of driving or so.

Answer 3

Don't rely solely on the temp gauge to determine if your AT is hot...The gauge is a reflection of your engine coolant temperature only. The vehicle needs to be driven for at least 10 to 15 minutes to allow the transmission to reach it's operating temp... especially if equipped with a separate transmission cooler.