Accurate Measurement of Trans Fluid EASILY
 

One of the biggest pain in the whatever is accurately measuring the level of transmission fluid you have in your car. This is an. easy and accurate way to do it. Once you get everything ready, the actual work takes only a few minutes.

Note: This assumes that you have TOO MUCH fluid in your transmission. If you aren’t sure, add some fluid so that you do.

Purchase some clean, new tubing. I used “Low Density Polyethylene tubing” This is the translucent plastic that is fairly stiff. My local hardware store had it in ¼ diameter for .13/foot, 5/16 for .19/ft and 3/8 for .25/foot. Buy about 3 feet of it to get you up and out of the dip stick area so you can hook on your suction pump. While you are in that section of the store, talk them out of a ½ inch long piece of a bigger size tubing that your tubing will barely slide into. This will be used as a “stop” to mark where the tubing will stop when inserted into the dip stick tube. By the way, I first tried using ¼ inch copper refrigeration tubing but it simply would not slide down the dip stick tube, so plastic is the way to go, but don’t use the soft, transparent plastic.

Get a suction device. I used a rotary “Jack Rabbit” pump, or you could use a suction brake bleeder rig or any suction device you have that won’t make a mess. Don’t even think about mouth sucking it out!!

Mark your tubing. Pull your dip stick, lay the tubing onto the stick, with the tip against the bumper that hits the inner shoulder of the dip stick tube. Do this carefully! Holding the tubing against the dip stick, next mark the tubing adjacent to the “Max Hot” mark on the dip stick.

Slide the small scrap of tubing onto the tubing to that mark. Now you should have a piece of the plastic tubing that will be inserted into the dip stick tube to the “stop” and be the exact length inserted that the dip stick is when measured to the Max Hot mark.

Get your suction pump ready to be attached to the top end of the plastic tubing and have your collection bottle ready.

Drive your car until the transmission fluid has been thoroughly heated.

Park your car in the level area, keep it running in Park.

Pull your dip stick, carefully wipe the new plastic tubing thoroughly clean with a lint free wipe. Insert it into the dip stick tube to the “stop” so the bottom of the tube will be where the Max Hot mark would have been.

Attach the suction device and pump out the excess fluid. You will now have the exact amount of fluid you should have in the transmission.

Pull the tubing, replace the dip stick and carefully clean up everything. If you are going to reuse the tubing, blow and wipe it clean and store in something like a clean zip lock bag.

By the way, in case you were wondering, I heated Dexron II to over 200 degrees and immersed a piece of the tubing for about 10 minutes. It held up well. Wear eye protection against drops of hot fluid flying around and wipe up any spills.

If it works well for you and are grateful, I drink Cabernet!:)

Best of luck,
Ron Johnstone

When my mechanic changed my fluid and installed the filter, he filled it up, took it out and drove it for awhile, then parked it, and checked the fluid level again, He added a bit of fluid, and gave it back to me. I check the level monthly.

Or disconnect the cooler hoses, you'll lose about 1/4qt.

But how will this service those newer models that have a dipstick tube, but only have the red plastic cap with no dipstick?

I just go with the method in the FSM; 10mm below the mark on a cold engine. Seems to work fine. Never could get a straight answer out of that dipstick with the engine all warmed up.

Aren't there two marks on the tranny dipstick? Are you saying 10 mm below the top (full) mark? I think it is hard to calc your exact level because you pour the fluid down the dipstick tube and that fouls the dipstick. I usually wait several minutes, then get frustrated, check it again and hope I have the correct amount in the tranny. A cold check would be easier.

from the FSM:

Note: Too low or too high a fluid level will affect
the operation of the transmission. The fluid level
should be checked regularly with the dipstick
from the engine compartment. When checking
fluid level, vehicle should be parked on level
surface.
The fluid level varies with fluid temperature. The
min. and max. marks on the dipstick are based
on a fluid temperature of 80°C (transmission at
normal operating temperature).
However, at a fluid temperature of 20-30°C the
max. oil level will read below the min. mark as
follows:
Transmission 722.0 30 mm
722.1 30 mm
722.3 10 mm
722.4 12 mm
722.5 10 mm


It's tricky no matter what.

With the 'cold' check for ATF level I assume engine is running???

Is there a cold engine not running point to do a check??? This would be the best way to gauge it surely???

Some information first:

Hot / Cold is trans fluid temp not engine coolant temp.

If you sit and idle, the engine will get hot way before the trans does.

Oil expands when heated.

The torque converter / front pump / cooler need to be full of oil before the level can be checked. ( Engine running )


So, for a trans that is at the proper fill level: If the trans is cold and engine not running , the level will not be accurate. In all cases the level will be higher than when running even though the fluid has contracted. This extra level comes from the torque converter / cooler / trans lube systems leaking down to the pan. The longer the trans site, the more will drain from the torque converter.

Cold not running checks are more for, " Is there any fluid in there?" and " We don't know the recommended fluid change amount, is there enough in there to start the motor? "

Also be aware, when adding fluid let it drain down the tube otherwise you will get a inaccurate smeared reading. Give it a minute or two, sometimes longer. ( the motor can be off for this but restart for the check. )

Thank you for this reply. Very good info.

My question is related to this approach and why is it not used by manf.

Assume car is sitting on level ground and is in a static condition which I will define as car at 70 degF for at least 12 hours without having been energized in any way (engine not run).

In this static state will not all of the draining have reached an equilibrium such that the cold dip reading level can now be accurately stated for a given vehicle type. If I use this method it is much easier to be consistent and accurate.

Give me your ideas on this and of course I will test it anyway. Bear in mind that I am assuming a standard production vehicle with an undamaged pan etc.

One missing variable in your theoretical car is trans temp at the time of shutdown. ( OK, two missing variables as we need a frictionless pulley in there somewhere. )

If the trans is shutdown hot, the leak rate will be higher than if the trans was shutdown at ambient.

Also consider that the leak rate would vary due to production tolerances and , for used cars, system wear.

Why can't the same logic apply to ATF static cold level as is applied to engine oil level. Both pump fluid up into a complex assemblage of components. I have for decades used a cold static dipstick measurement for the engine oil and and it is repeatable from day to day and is very simple.

I thought 80°C was an intermediate temperature for the transmission. Is this the typical temperature for a fully warmed transmission?

The fully warmed temp will be a function of ambient plus a whole bunch more. The heat being dissipated by the cooler and tubing; engine temps which will vary with a/c on and off, etc. It is not possible to quote a maximum so a typical is what you get.

This is why I like the idea of a static reading for ATF level but it seems that automotive engineering refuses to go along with the simple idea.

97SL320 makes some very good points but I feel there is more to the story.

speaking of reading dipsticks, try deciphering what SAAB recommends for their 4 cyl engines, the cap is the dipstick too.

check the oil level after hot shutdown within 2 minutes.

I have read a similar thing on a very old Honda autobox, check within 50 seconds of shutdown, WTH - the dipstick was about 4 inches tall buried near the diff carrier. So you burn your arms trying to check proper level.

the MB procedure is pretty simple like any other car.