Checking trans fluid, what's the right way?
 

I'm afraid I've been checking the transmission fluid wrong all these time with my 300SE. This is what I do: running, operating temperature, transmission in P, dipstick out, clean, all the way down and check.

And on a level surface. Make sure you have run it for minimum 20 minutes.

Driving it, or just run the engine?

Your method is correct Jorn.

At least 10 minutes of driving will get you up to temperature. Simply idling may get the engine up to temp but it will not get the transmission temperature up. Then stop (of course), run the shifter through all the gears stopping in Park, engine running and check.

That makes sense.

Rule of thumb for the fluid is if you can’t comfortably hold the tip of the dipstick, it’s probably at the operating temp of 180*F.

Then measure it after the car sits overnight and you have a reasonable way to check cold.

Sixto
98 E320s sedan and wagon
02 C320 wagon

And why would you check it cold?

Preferably check it at temp but if you want a quick check after a fluid change or before a trip...

Sixto
98 E320s sedan and wagon
02 C320 wagon

Got it. My mistake was that I didn't drive it prior, I always would let the car idle until it was up to temperature. I should have known better. Got it up to the right level today.

It takes a long time to get tranny fluid up to temp with vehicle just idling.

The problem with my SD is that I cannot read it on the dipstick. It is always smeared or just not at a definite level. I have considered grinding out a small V in the dipstick thinking the tranny fluid would cling to the V.

Anyone tried this?

Other cars have dipsticks with pinholes. Either there’s fluid in the hole or there isn’t. Some have a dimple but even a dimple is difficult to read.

Sixto
98 E320s sedan and wagon
02 C320 wagon

Lets not overthink this. Jorn asked a simple question and got his answer. No real reason for this thread to grow legs. It can only confuse

I noticed that I could not do this "rule of thumb" repeatedly - upon my yearly doctors exam I came to know Im diabetic now, I just prefer to use my homemade thermistor in a tube sent down the dipstick hole, it wont lose nerve sensitivity over time :D

Fresh clean fluid sure makes it easier to check the level.