Drove Vehicle Below "Low" Mark On AT Dipstick

Question

I drive a 2001 Chevrolet Prizm with 108k miles and an automatic transmission. I didn't refill ATF to correct level after dropping the transmission pan. I used the "COLD" reading on dipstick to measure the fluid level on a flat, level, surface as I only drove it for little over a mile before checking it. After going through gears and letting it idle for 3-5 mins, I check it using the "COLD" Mark and it shows that the level is full. So, the next day after driving 120 miles, and it was acting a bit unusual, but nothing out of the ordinary as it has had on occasion some rough shifting from time to time since I bought it at 62K miles. Anyway, I check it again going through the same functions, but letting it sit for 30 minutes after driving 120 miles(highway driving) using the "HOT" marks on the dipstick. I then come to find that it's exactly between the hot and cold reading levels. To which I then added another quart and brought it to in between the two marks on the "HOT" level. It starts to shift just a bit better after that extra quart too now. 
Now that you have an understanding of what exactly happened, do you estimate that it's likely I damaged my automatic transmission in the long run?
Thank you,

Matt

Jacksonishere · Accepted Answer

Maybe hopefully you caught it quickly. And at the very least it had fluid in it when you did drive it. Hopefully it wasn't very far.

Inthedetails · Answer

So here is a little tip, not just for you but also for anyone reading: the cold measurement on the dipstick is an approximation. Its not recommended to use that measurement as definitive/exact. This is a very common mistake. In the vehicle manual it will say to only use the cold measurement to get an approximation. If you only drove it for a few miles like that it should be fine but you might have increased the wear a little on the transmission overall. I wouldn't stay awake at night thinking about it - just make sure you check it a few more times to make sure its staying where it should (HOT).

As an informative note the reason the cold measurement can be inaccurate is because transmission fluid is so thin that ambient, outside air temperatures can throw the reading in one or the other direction. Most likely when you did the first (COLD) check it was warm outside and then when you did the second (COLD) check it was cooler out.