Honda 6AT Fluid Level Caution

[The Critic]

Honda's older 6-speed automatic transmissions have a dipstick. Easy enough, right? Not quite...

A recent TSB, #23-073, states that overfilling the unit will increase fluid foaming and contribute to a known fluid overheating issue.

https://www.piloteers.org/attachments/a23-073-pdf.171724/

Here is where things get interesting:

Honda specs a 3.3 quart capacity for a drain and refill. If you drain the trans on a level surface and refill with this amount of fluid, the fluid level may not even register on the dipstick if the transmission fluid is cool. The marks on the dipstick are only for "hot" transmission fluid - fluid that is in the 176-185F range.

Why is this an issue? If you do a short drive around the neighborhood, you may get the engine coolant warm enough for the radiator fans to come on....but the trans fluid may still be barely warm.

On two RDX's I've serviced, 3.3 qt of fluid and a <100F AT fluid temp resulted in the level being 2-3mm below the hot minimum mark. On a Pilot, which has the shorter dipstick, the fluid was barely touching the tip of the dipstick. Natural inclination would have been to add more fluid, but I resisted. I wasn't able to drive any of the vehicles long enough to reach the 176-185F fluid temp range, but I strongly suspect that 3.3 qt is just enough fluid to reach the hot minimum mark when checked at the correct temp.

Moral of the story? Fill the transmission with the specified amount. Make sure you're aware of the actual trans fluid temp (via scan tool) if you are measuring level using the dipstick. Otherwise, you can easily overfill the transmission.

 

[michaelluscher]

A good warning

I thought I was doing it right for a while, but now with a decent scan tool I can be precise with level checks to a specific temperature
This is a make/model agnostic philosophy

I wonder what the software update in the TSB does?

 

[JHZR2]

Good to know. It’s easy enough to measure volume poured in. Makes me want to do a spill and fill just in case…

The temperature/level issue is known. I recall @clinebarger showing graphics of this for Chrysler 47RE or a similar AT.

 

[TheLastWord]

On a related subject, does the 5 speed used in 07 Civic have the same issue? Owners and service manual instructions are specific for time to test after warming up, but does not state a temp.

 

[RyanY]

Related question becUse i do not know the configuration of the Honda trans structure...if you drain the ATF when hot, does more come out than when it is cold? Or does the same amount come out regardless of temperature?

 

[edyvw]

Why manufacturers went away with transmission dipstick!

 

[tbm5690]

Interesting. I've always done drain and fills on the MDX using a bucket with measurement lines to ensure that I am putting the same amount of fluid back in, both at room temp. I am genuinely curious to know if this would allow longer intervals without the typical slipping that occurs when DW-1 gets too old/hot. Doubt it, as the TSB specifically mentions the overheat warning and not general performance degregation.

 

[nicholas]

Interesting. I've always done drain and fills on the MDX using a bucket with measurement lines to ensure that I am putting the same amount of fluid back in, both at room temp. I am genuinely curious to know if this would allow longer intervals without the typical slipping that occurs when DW-1 gets too old/hot. Doubt it, as the TSB specifically mentions the overheat warning and not general performance degregation.

I highly doubt it.
DW1 does not hold well for large loaded vehicles.
Especially vcm, which does sound strange trans stuff when activating.

 

[supton]

Makes you long for when they had a drain plug and a fill plug. Fill until it dribbles out the fill plug. Done.

Granted, you had to row your own gears, but life was arguably simpler.