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I was helping out a friend yesterday who was facing some issues with a transmission-related CEL on his automatic 2003 Mazda6.

When we checked the ATF dipstick the transmission fluid was a clear light-pink color (so probably freshly-changed by a previous owner) and well above the max level mark.

The dipstick had two markings - 20 °C and 65 °C. It was well above the 65 °C mark when I checked it with the engine warm (say 60-80% higher). I also asked my friend to check the level later on with the engine cold. It was still well above the 65 °C mark.


In my experience, the old fluid is discharged through a drain plug, then new fluid pumped in through a fill plug hole. Once the new fluid starts dripping out of the fill plug hole, the amount of fluid is at the "right" level. This is also confirmed by this answer to a related question.

With this in mind, how is it possible that the transmission fluid was overfilled? Am I missing something? I suppose someone could have topped up through the dipstick channel itself but that doesn't seem like the right way to do this. Of course, I could be wrong about it.

My concern is that the dipstick might not reading the correct amount of transmission fluid due to some kind of internal blockage, especially since the ATF fluid looked pristine.

  • Not sure about a Mazda6, but how does your link about checking fluid in a Chevy Cavalier equate to the Mazda? It could be the same, but most likely not. – Pᴀᴜʟsᴛᴇʀ2 Aug 11 '15 at 12:52
  • @Paulster2 : That Cavalier example is what I am familiar with. I don't know if there is another means to top up ATF; just citing what I know. – Zaid Aug 11 '15 at 12:54
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Most cars do not have drain plugs for the transmission in my experience. In fact, I have only seen it on one, which had a plug because the car had a permanent transmission filter.

That said, it is very easy to overfill transmission fluid.The link you posted is an example of a cavalier. GM took out the dipstick to prevent inept owners from overfilling the transmission (at least that's their story). Frankly, it's annoying, but if someone can jack up a car and put it on jack stands, they probably know what they're doing with regards to filling a transmission.

If you are worried about the tranny, get a new filter, drop the pan,use a graduated drain pan to measure how much came out, look for an excess of metal shavings at the bottom of the transmission pan, these are a real cause for concern, put in the new filter, refill to what the dipstick says is the right amount.

If you drained 7 quarts, but only put back in 5, it was obviously overfilled.

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I do not believe that all automatic transmissions have drain/fill plugs. I had a 1993 Ford Explorer where this was the case - I had to drop the pan to drain it (and replace the filter) then had to refill it through the dipstick tube with a funnel.

This being the case, I do not think it is outside the realm of possibility that the previous owner did not know about the fill plug. So, he drained it with the handy drain plug then filled it through the dipstick tube - that's what I would have done. I wouldn't have overfilled it though...

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As I have done in the past: Just drain some fluid out, then top off thru filler tube using funnel.

http://forum.mazda6club.com/engine-drivetrain/126047-draining-6s-automatic-transmission-fluid.html

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What temperature was the fluid when you measured it? IIRC ATF expands quite a bit with heat, and you'll often see separate cold and hot marks on the dipstick...

  • The dipstick had two markings : 20 °C and 65 °C. It was well above the 65 °C mark when I checked it with the engine warm (say 60-80% higher). I also asked my friend to check the level with the engine cold. It was still well above the 65 mark – Zaid Aug 11 '15 at 9:12
  • Ah! Can you undo the filler plug and allow it to drain down to the correct level? – Nick C Aug 11 '15 at 9:19
  • I've already asked him to take it to a mechanic to drain it down. I was hoping to understand how it was overfilled in the first place – Zaid Aug 11 '15 at 9:36

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