mclasser

I recently changed my radiator and despite my best attempts, ATF kept dripping out of the tranny cooler lines so I had to top it off. I topped off the fluid and re-checked it after the tranny was hot after a highway drive; the level was properly within the cross-hatches for HOT.

Fast forward to today-- Had to drive several hundred miles for a trip and I noticed the tranny was shifting hard/jerking on the highway. Nothing too severe but definitely noticeable. I pulled over to check the ATF level and the dipstick read about 1/4th (maybe more) of an inch over the max line. I surmise that with the 85°+ temps today and long highway driving, the ATF fully expanded and registered as overfilled in the system. The service area I stopped at had a gas station garage. I asked the lone guy there if he had a fluid pump I could use to pull out the excess fluid via the dipstick tube. Of course, he didn't. I had no choice but to keep driving to my destination. I plan to pick up a small pump tomorrow and pull out some fluid.

I hope I haven't done any long term damage to my tranny. I only noticed the jerky shifting in stop-and-go traffic. And like I said, it wasn't too bad. Do these cars have a breather/vent tube in case of overfilling?

Child_uv_KoRn

iTrader: (7)

Overfilling doesn't matter. Every maxima I see has been overfilled up to an inch over the full line.

Yes, there's a vent tube.

chrome91

iTrader: (1)

to a degree, trans oil and motor oil you can often go a quarter inch above the full line and its perfectly fine. anything more you risk foaming of the fluid that can wreak hell on bearings and clutches

maxiiiboy

Yes, the rotating crankshaft can foam the engine oil (when oil level in the crankcase is too high); and foamed oil does not provide good lubrication.
Not clear to me: how does ATF foaming happen?
I also heard the argument that overfilling the ATF will "bust the seals". This does not make sense with the Maxima where the AT has an open ventilation tube.
Can somebody explain what exactly happens when an AT is overfilled?

talkinghorse

iTrader: (121)

A quarter inch over max line shouldn't hurt anything and might well be expected since you had just pulled off the highway...Nissan and others even tell you that you can't get an accurate reading immediately after highway driving. Chances are when you check it today it will be within operating range.

If not, just suction a little bit out as you intend to do.

chrome91

iTrader: (1)

theres stuff rotating in the auto trans too. sun shell, casing, etc. you get pockets of foamy air in some of those places, no bueno

otherwise youre gonna be blowing out seals too

maxiiiboy

Your statement does not explain anything.
To blow out seals, there must be (significant) pressure. Can you explain how the pressure is going to build up as a result of overfilling, in a space that is interconnected with, and ventilates into, the outside atmosphere?