Q: How do you accurately check your automatic transmission fluid? Hot, cold, running, put all gears through, then check?

Typically, the fluid level is checked both hot and cold in order to provide a cross check. Checking initially when cold is easier as you are not hovering over a hot engine holding a hot dipstick. Basically, on a flat level surface, start the vehicle’s engine and immediately run through each gear, pausing just momentarily.

Finish with the car in "Park" and leave it in "Park". Withdraw dipstick and wipe it clean with a LINT FREE cloth (lint and dirt causes problems in transmissions). Reinsert the dipstick after you have wiped it and upon withdrawing it. See if the fluid level is within the cross hatched area marked below a "C" (for cold).

Sometimes you have to look at BOTH sides of the dipstick in order to gauge the level. If the level is in the "C" area, you are likely OK, but to be sure, drive the car for about 10 miles and re-check the level, this time looking at the cross hatched area marked below the "H" (run through gears as before, and leave in "Park").

If the fluid level is OK when cold, it should also be within the cross hatched area for "H" as well. The reason for checking when both hot and cold is transmission fluid expands as it is heated. Note that if you drive the car at highway speed for a long period of time and then attempt to check the fluid level "hot" after that you WILL get a false reading (the fluid level will appear "high", when in fact, it is perfectly OK). So, when checking if it’s hot, you can’t do that check if you just drove 50 miles across the desert because the fluid will have expanded. Transmission fluid expands and keeps expanding the hotter it gets. Dipsticks are calibrated to "normal" hot operating temperature (i.e., the 10 mile suggested drive; longer in winter). If the transmission fluid has been in your vehicle for more than 100,000 miles, change both the fluid and the filter, which maintenance will help promote the longevity of your transmission. Modern synthetic transmission fluid of the right type is recommended. If you are in need of a transmission fluid service, a certified technician from YourMechanic can come to your car’s location to perform this.