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Discussion Starter #1 (Edited)
I've changed transmission fluid in multiple vehicles and there is always a temperature range the transmission is supposed to be within to check if you have the correct level. I can't find any mention of this for a smart 451...

I drained my transmission fluid today on a 2015 smart 451 with 28k miles and refilled with exactly what came out but it never overflowed from the fill bolt. I read that the transmission is full when it overflows from the fill bolt, which could be correct, but, at what temperature? I'll check how much I used tomorrow but my guess would be around 2.3l. It looks like most people report adding 2.5-2.6l to their 451 when changing. Could my 451 have burned or leaked 0.2-0.3l since new, was it underfilled at the factory, or is it supposed to overflow from the fill bolt when hot? Is this transmission designed differently in some way to where the level does not need to be checked while hot? And if the level is supposed to be checked when hot, at what temperature?

Any thoughts fellow 451ers?
 

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Discussion Starter #3
Interesting! From what I see online most 451's take 2.5l before overflowing from the fill bolt. If alldatadiy capacity is correct then filling until it overflows from the fill bolt may be overfilling.

Do we have any smart mechanics that can check their service manual for a level check procedure? (I'm hoping the factory procedure may list a temperature range for the level check)
 

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Discussion Starter #5
Does evilution pull there info from the mercedes Wis/service manual?

Maybe the weight of the oil is so heavy that it doesn't change much when hot. If no one here is a Mercedes/smart tech I'm going to ask someone I know that runs a euro shop if they can pull up the level check procedure for me from the Wis.

It is odd that everything says 2.3l but most take more. Maybe I'm being anal but I don't want to over/underfill it.
 

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I wouldn’t think temperature of the fluid or transmission metal parts is as critical for manual transmissions as it is for automatic transmissions, and that is basically for accurately checking fluid level. Refill until it begins to weep from the top opening is the proper procedure.
 

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Discussion Starter #8
I read the genuine Mercedes/Smart tech drain/fill transmission oil procedure... The only thing I noticed is that you are supposed to drain it with the engine at operating temperature. I drained it cold, if I had drained it at operating temperature more fluid would have drained out (I think) and if more fluid had come out I could have probably filled it until it reached the "lower edge of filler opening" as the drain/fill doc says to. Because I drained it cold and refilled with the same amount I am probably fine but my next change I will drain it at operating temperature and see if takes any more/less. Btw the drain/fill bolt torque is 43 Nm 31-33 ft-lb if anyone wants to know.
 
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