ATF temperature question

[skaughtz]

Can someone explain why you want to heat up the transmissions fluid in the car when you are changing it? I understand the need to get the engine up to operating temperature when you are testing the level of the ATF, but not when you are changing it.

For instance, if your car is at ambient temperature, and your new ATF (in the bottle/jug/whathaveyou) is at ambient temperature, and it is important to replace the same amount of fluid that you drain out, why would you want to heat up the fluid inside of the car before adding in the new fluid (thus making its characteristics different from your new fluid)? Wouldn't that throw off your measurements when comparing what was removed to what is being added?

Is there something that I am missing? I recently did a simple drain and refill on a Civic that was cold (ambient) and after a good long test drive on the highway to heat it up the ATF measurement was exactly where it should be. But I keep reading that you should heat up the liquid first when changing it.

 

[Lolvoguy]

Originally Posted By: skaughtz
But I keep reading that you should heat up the liquid first when changing it.


first time I'm reading this. I;ve heard this for engine oil, but not trans fluid.

For an AT, you usually need to only warm the fluid for checking the level, not for changing it

 

[skaughtz]

I guess the same question applies to engine oil then. I assume it is to get it to flow better and thus drain more of it since you are typically refilling it by what the capacity is stated in the owners manual? Of course, wouldn't that then leave more within the engine components rather than collected in the pan or would that be negligible?

Glad I'm not the only one confused about my ATF question though. I've definitely read suggestions to do that

 

[horse123]

If your car doesn't have a transmission dipstick (not too common anymore I don't think), then you don't replace the amount you take out, you replace it until it's up to the fill hole, like in a differential.

 

[skaughtz]

Originally Posted By: horse123
If your car doesn't have a transmission dipstick (not too common anymore I don't think), then you don't replace the amount you take out, you replace it until it's up to the fill hole, like in a differential.


That makes a bit more sense. I have a 2007 Camry and a 2012 Civic and both have ATF dipsticks (Camry has a tube and the Civic has one that goes straight into the transmission). I'm glad I went with my gut on the temperature thing

 

[meep]

depends on the change method?

if it's a cooler line fluid swap, some transmissions bypass the cooler circuit until a certain temp is reached. pan drop -- not sure it matters.

 

[dlundblad]

I would think the main reason you'd want to heat it up is to get the fluid flowing more feely. Plus if the ATF had any contaminants, they would be in suspension in hot (recently stirred up) fluid.

 

[HTSS_TR]

I use a fluid extractor to siphon ATF via dipstick tube, the warmer the fluid the faster it can be extracted. The Mityvac 7201 can extract 4 quarts ATF in less than 7-8 minutes if it is above 130-140F after a good drive, it took more than 10-12 minutes to extract the same amount in a cold stone engine/transmission early morning.

It had been a long time I do any draining of ATF or oil, the Mityvac is the work horse in changing those fluids.