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Perils of overfilled transmission?

Discussion in '80-Series Tech' started by e9999, Jul 1, 2005.

  1. e9999

    e9999 You want to do what...? Moderator

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    Haven't seen much on this topic.

    What are the potential problems associated with having too much fluid in the transmission? Anything serious? What?
  2. Koffer

    Koffer SILVER Star

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    This is what happens. :eek:
    see same color and everything

    Attached Files:

  3. e9999

    e9999 You want to do what...? Moderator

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    wow! even the flares flew off! :D
  4. CreeperSleeper

    CreeperSleeper Cascade Cruisers Prez. SILVER Star

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    That has been an old wheeling trick for years. (Extra ATF, not the pic) I would see if the tranny slipped on steep hills at all. If it does, add a little and see if it helps. The only downside that I know of is adding too much will cause leaks.
  5. IdahoDoug

    IdahoDoug New Member

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    8,780
    I've driven a couple vehicles, including both 80s, with an extra quart in them for periods of up to a year including some heavy towing. I don't recommend it, but if you find it like this no cause for panic. It's actually pretty simple to put a drain pan under the 80 and pull the tranny drain for 5 seconds or so before slapping it back in. You'll have a messy hand, but that's about the extent of it.

    DougM
  6. e9999

    e9999 You want to do what...? Moderator

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    why not recommend it? what do you think would happen?

    well, of course, the fSM recommends a max amount, can't be left open on the max side or people would try to put in 10 gals but that does not mean it would damage anything automatically, right? Anything mechanical worse than spilling everywhere?

    Not that I plan to do this, just curious...
  7. alaskacruiser

    alaskacruiser New Member

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    Like LR_RESQ says, I think it makes you more prone to leaks. Leaks started on my '93 when I accidentally overfilled it. No sign of leaks before that, and the overfill was well after the tranny fluid changeout.
  8. e9999

    e9999 You want to do what...? Moderator

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    what kind of leaks?
  9. turbocruiser

    turbocruiser SILVER Star

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    ATF leaks, I would imagine! :rolleyes: :D :rolleyes:
  10. e9999

    e9999 You want to do what...? Moderator

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    evidently we are not talking about cranial cavity overflowing here... :D :D :D :D :D
  11. CreeperSleeper

    CreeperSleeper Cascade Cruisers Prez. SILVER Star

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    LOL! Probably around the pan... The leak that is.

  12. alaskacruiser

    alaskacruiser New Member

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    Yes- leak was around the pan. I thought this was obvious. ;)
  13. turbocruiser

    turbocruiser SILVER Star

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    Hahaha, my cranium runneth over! :flipoff2: :D :flipoff2:
  14. IdahoDoug

    IdahoDoug New Member

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    I have no real world data on this, but it's my understanding that you can overheat the tranny from overfilling. I honestly cannot recall why this happens, as it's not like an overfilled engine where the cranks start slapping the oil and foaming it. A tranny depends upon pressure against one side of myriad valves and parts with no fluid and/or fluid pressure against the other side to properly move and apply proper pressure. If there's fluid where it shouldn't be, I could see issues arising almost immediately.

    DougM
  15. NMuzj100

    NMuzj100 New Member

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    I see mixed opinions on this. Looks like it might vary from tranny to tranny.

    From Tranny Shop FAQs -

    Will it hurt to overfill the transmission fluid?

    Not really, but because transmission fluid doesn't compress, and air does, severe overfilling may make the fluid become aerated. This could cause abnormal operation. ​

    Will it hurt to overfill the transmission?

    In a word, no! Although, it is possible that gross overfilling can cause the fluid to be subjected to moving parts and become aerated which could cause abnormal operation. You may also notice leaks that ordinarily would not occur.

    Will overfilling "blow" seals?

    In a word, no! The transmission case is vented preventing pressure buildup in normally un-pressurized areas. Severe overfilling can raise the fluid level such that the transmission may lose fluid through the vent or leak from seals that are above the normal fluid level, but the fact remains that the seals that are under pressure and those that are not will not change because of the fluid level.​

    And the Car Talk guys

    Dear Tom and Ray:

    Does it harm an automatic transmission if the fluid is well above the "full" mark on the dipstick? Lynn

    Tom: Apparently it does. You may notice a little warning that says something like "Caution: Do Not Overfill. Overfilling May Lead to You Making Your Mechanic's Boat Payment This Month."

    Ray: But I have to admit, I've never personally seen a case where overfilling has caused any damage to an automatic transmission. I've just seen the extra fluid leak out.

    Tom: I suppose what can happen is that the oil can foam and "froth," kind of like a root beer float. And if it's foamy, the fluid won't be able to adequately lubricate the transmission, and it gets damaged.

    Ray: But this only a theory. We've never actually seen any evidence of this occurring. So in the interests of science, I'm conducting a little experiment as we speak. On my way home last night, I stopped and put a quart of IBC Root Beer in my brother's transmission. And I guess we'll see what happens. ​

    From a insurance trade paper
    An Assembly of Experts
    By Garrett Engineers, Long Beach, CA

    Our expert was assigned to inspect a pickup truck that suffered an engine fire while pulling a trailer. The owner/driver, reported that he saw a light-colored smoke in his rear view mirror and started to pull off the road to the right-hand shoulder. When he stopped the vehicle and looked under the right front fender he saw the roadside grass on fire. The owner also reported that the vehicle did not have a history of oil leaks of any kind, that he kept the vehicle serviced on a regular basis and that the transmission had been recently serviced (including filter and fluid replacement). He also reported that the trailer was not loaded to full capacity and that he was not exceeding the speed limit at the time of the fire.

    Our expert examined the vehicle and its burn patterns. The fire damage was most intense at the level of the transmission dipstick and faded as it went forward and up the engine block. The damage indicated that the origin of the fire was transmission fluid that overflowed the dipstick tube and was ignited by the catalytic converter in the exhaust system directly below the dipstick tube. Confirmation of the transmission overflow was gained by viewing the underside of the vehicle. The transmission housing was coated with an oily fluid. There were no oil stains on the oil sump or the exhaust crossover pipe, indicating that the coating did not come from the front of the vehicle and was not engine oil. The transmission fluid coating appeared fresh and had no evidence of collected road dust or debris, confirming that the leak was recent and supporting the driver’s “no history of oil leaks” statement.

    Transmission fluid expands as it is heated. There is a significant difference between the volume occupied by cold transmission fluid versus normal operating temperature transmission fluid. This is why transmissions (among other things) should never be overfilled. When they are overfilled cold, and then run to normal operating temperatures, the fluid expands and can run out the filler tube or dipstick tube. In this case it dripped down onto the very hot catalytic converter, and then caught fire. The pickup truck’s recent transmission service was the most likely cause of the overfilling of the transmission, which caused the fire.​
    Last edited: Jul 2, 2005
  16. honk

    honk New Member

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    The possibility of a vehicle fire is real.

    The place I once worked lost a brand new Ford truck this way. It literally burned to the ground. The truck was pulling a trailer over Pacheco Pass in Gilroy, CA on a hot day. The fire investigator hired to examine for cause determined that the fire resulted from the expansion of overheated transmission fluid having puked from the fill pipe and being ignited by the exhaust system. Since the truck had received a first servicing only two days before it was concluded that the trans. must have been overfilled because of the incorrect procedure used to check the level bringing the mechanic to add fluid where none was needed.

    So, it is not advisable to overfill automatic transmissions, and particularly ill advised in vehicles equipped with catalystic converters because they are often hot enough to ignite oil.

    The oil's capacity to expand is why most if not all level checking protocols instruct that the level be checked either hot or cold as specified on the dipstick, usually.
  17. e9999

    e9999 You want to do what...? Moderator

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    great info!
    thanks.

    Another tip of the hat to Toy may be due here since they put a seal on their trans dipstick and a retainer clip. This should limit leaks there I would think...

    So the above confirms/suggests that problems would not be of a mechanical nature. Sounds right.
  18. Hayes

    Hayes New Member

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    Good thread.
    Assuaged my concerns about a (very slightly) overfilled tranny.

    Hayes

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