How hot should my engine be to check the transmission fluid on my 2000 Subaru Outback?

Hi there car experts,
I recently bought an automatic 2000 Subaru Outback, and changed the transmission fluid and filter. After changing the fluid/filter I drove the car around for about 10 minutes to warm it up and checked the fluid level according to the user’s manual instructions. The level was between the low and high marks on the hot range of the dipstick, so I figured all was well.

This weekend I drove the car 300 miles to visit my mom, and checked the transmission fluid right after the long drive. This time, it was 1/4 inch above the full line on the hot end of the dipstick range. The next morning I drained a cup of fluid, drove the car for 10 minutes, and checked the transmission fluid level again. It was just below the low mark on the hot end of the range, so I added 1/2 cup of fluid to the transmission.

On the way home from my mom’s house, I stopped to get gas after driving for an hour and checked the fluid levels. Again, the transmission fluid was above the full mark on the hot range.

I’m pretty sure I followed the right procedure to check the level - I shifted through all the gears, then checked the fluid on the hot range on the dipstick while the car was running and on a flat surface.

So the question is, what I’m doing wrong? Is a 10 minute drive too little time to warm up the transmission? Or could the transmission be too hot to get an accurate reading after I’ve driven for over an hour?

Any advice would be greatly appreciated…Thanks!

@Saskia fluid expands with heat, so I wouldn’t worry about it too much. It’s possible that the ATF wasn’t at normal operating temperature after that 10 minute drive.

Operating temp but not after driving for so long. Driving ten minutes may not be enough to fully warm up the fluid. After a long drive though you should let it cool off for a little. That’s my experience and what I was told anyway by the old guys.

The OM on one of my cars states that after long drives, let the car cool for 30 minutes before checking the level. Now, I had not seen this on my previous manuals, but as mentioned, it makes sense. After a long drive the ATF is just too hot and also probably splashed all over the place, so the level is not accurate.

Transmission fluid is normally checked with the engine idling and fully warmed up. The gear shift should be in neutral or park, depending on the car, with the handbrake on of course.

After a long fast trip, I agree that you should let the engine idle for a few minutes to normalize the operating condition. The fluid will still be moving around, of course. Some cars have a “cold” reading on the dip stick. That’s handy, but the engine still has to be running.

When checking ENGINE OIL, its necessary to shut the engine off and let the oil run down to the bottom of the engine. This will take no more than 5 minutes if the engine is warmed up. Alternately, check the oil before starting up the engine. That will show the true level, since all the oil will have settled in the bottom overnight.

Are you checking in Park, Neutral, or Drive? Make sure you do it right. Or you can always drain out a little after a trip and put it back before driving again.

Thanks for the advice everyone! I will try letting the engine idle for a while after a short drive and see if it makes a difference in the reading.

In response to Elly - I have always checked the transmission fluid by driving for at least 10 mins, pulling over, shifting through all the gears with the car still running, putting the car in park and then checking the fluid with the car running. The Subaru manual was not very spesific on how many minutes to allow the engine to warm up before checking the fluid, but did specify that the car should be in Park.

You can probably check it cold if you like, doesn’t it have a “cold” mark in the stick? Don’t sweat the little things! Did you ever hear the country song “Shut Up And Drive”??

I did what you all said and it worked! I took a short (3 minute) drive to the burrito shack, then left the car idling for another 5 minutes as I waited for my burrito. Before enjoying my delicious lunch, I drove for 3 more minutes, parked the car, shifted through all the gears, then checked the transmission fluid with the engine running. The fluid gauge said that the fluid was at the perfect level, right between high and low! So it looks like the fluid must have just been too hot the other times I checked. Thanks again for the advice everyone!