How to Check Transmission Fluid?

Kurb

Original poster
Member
May 3, 2014
89
Dumb question I know. I’ve been checking the fluid in several different vehicles for many years without giving it much thought - until this week. I normally start the vehicle, shift through all the gears, and then let the vehicle idle for 10 minutes before checking the fluid.

I was recently helping a friend work on his Chrysler minivan, and I found several transmission codes, which is normally a sign of low fluid. When I went to check the fluid, I learned that there was no dipstick. I looked it up online and people were recommending scoring cold and hot marks on the oil dipstick, and the hot marks were for a fluid temperature of 200 deg. F.

That raised my curiosity. My Grand Prix has this cool feature where I can display transmission temperature on the dash. I watched the temperature and realized that it normally does not even make it to 200 deg. F, at least in the Winter, unless I drive it really hard. The temperature also does not stabilize until I have been driving for about 30-40 minutes. It is only ~100 deg. F after 10 minutes of driving. Thus, I have been checking the fluid warm instead of hot for several years.

I understand that checking the fluid cold is not the best due to ambient temperature fluctuations. Is it best to check it warm or completely hot? What is the correct fluid temperature for checking the level? Is it vehicle specific? If so, what is the proper temperature for my Trailblazer? Does it really matter that much?
 
Dec 5, 2011
574
Central Pennsylvania
The cold mark is a minimum level when cold. Start, shift through all gears, idle for a little if you want before checking fluid. It should not be below the "cold" mark. If you're checking the fluid after doing an italian tune-up, the level shouldn't be above hot line and definitely never below the cold line. That's how I've always done it.
Many manufacturers are or have moved to "sealed" transmissions - i.e. no fluid checking by owner. The idea is that the quantity in the tranny should never really drop for any reason between recommended transmission services. It sucks for the owner if they choose to not use a dealer or servicer that follows manufacturers recommended service procedures and instead does it themselves.
 
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