Why do most car makers specify checking the ATF hot after a 20 mile drive or so and checking in park with engine idling, why don't they reference where the operating level is correct hot and then mark that on the dipstick so one could check it in the morning without having ever starting the car, I suppose I could check it hot like instructed then let it cool and mark that on the dipstick, not trying to sound paranoid but I do like checking the oil cold and would like the same for the ATF.
Checking ATF when cold after noting hot reference
- Thread starter zach1900
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cold can be -10° or can be 100°....
hot is a much narrower range, and you're sure the cooler is full of oil.
hot is a much narrower range, and you're sure the cooler is full of oil.
Originally Posted By: Jetronic
cold can be -10° or can be 100°....
this
cold can be -10° or can be 100°....
this
Originally Posted By: Jetronic
cold can be -10° or can be 100°....
hot is a much narrower range, and you're sure the cooler is full of oil.
Good point, I was just thinking "cold" meaning the engine hadn't been run in 6 hours + regardless of ambient temps, but I guess that's the point you made, ambient temps probably do have a bearing on ATF fluid as is "expands" with heat.
cold can be -10° or can be 100°....
hot is a much narrower range, and you're sure the cooler is full of oil.
Good point, I was just thinking "cold" meaning the engine hadn't been run in 6 hours + regardless of ambient temps, but I guess that's the point you made, ambient temps probably do have a bearing on ATF fluid as is "expands" with heat.
Jetronic is on the right track. Temperature makes a big difference with ATF.
JTK
$100 Site Donor 2025
Could be the potential of a wide ambient temp swing like mentioned, or it could be because chances are it's going to be warm/hot when it's in a shop being serviced.
Originally Posted By: zach1900
Why do most car makers specify checking the ATF hot after a 20 mile drive or so and checking in park with engine idling, why don't they reference where the operating level is correct hot and then mark that on the dipstick so one could check it in the morning without having ever starting the car, I suppose I could check it hot like instructed then let it cool and mark that on the dipstick, not trying to sound paranoid but I do like checking the oil cold and would like the same for the ATF.
You can do that with a bit of practice and reference...
The big problem becomes some trans have "valves" or more like thermostatic reeds that keep more fluid up in the housing or upper valve body/pan when hot or cold that can skew readings alot. That being said you can do this a number of times hot and cold and establish a "benchmarK" for where it should be cold for your checking purposes. Most times tho, OEM doesn't bother with this for trans... or for engines for that matter - because of these reasons.
BurrWinder
Why do most car makers specify checking the ATF hot after a 20 mile drive or so and checking in park with engine idling, why don't they reference where the operating level is correct hot and then mark that on the dipstick so one could check it in the morning without having ever starting the car, I suppose I could check it hot like instructed then let it cool and mark that on the dipstick, not trying to sound paranoid but I do like checking the oil cold and would like the same for the ATF.
You can do that with a bit of practice and reference...
The big problem becomes some trans have "valves" or more like thermostatic reeds that keep more fluid up in the housing or upper valve body/pan when hot or cold that can skew readings alot. That being said you can do this a number of times hot and cold and establish a "benchmarK" for where it should be cold for your checking purposes. Most times tho, OEM doesn't bother with this for trans... or for engines for that matter - because of these reasons.
BurrWinder
JTK
$100 Site Donor 2025
Any time I do an ATF drain/fill, I do it at a ~62-75F ambient temp and I just add back the amount that came out.
I just realized my ATF dipstick does have a "cool" and "Hot" upper and lower factory markings, not sure what they mean by "cool" as in just starting an engine that's been sitting overnight or what, also the dipstick is dark colored as opposed to the oil dipstick which is shiny.
I am probably overthinking it as in 20 years of vehicles I have never had an ATF fluid fluctuate.
I am probably overthinking it as in 20 years of vehicles I have never had an ATF fluid fluctuate.
My current car has hot and cool markings on dipstick, and manual says less than 80-90°f for cool & 180°f+ for hot, iirc.
Mine shows dead on full if checked hot, but fluctuates when checked cool and almost always shows overfilled, especially as gets colder out.
So I check hot 90% of time.
Mine shows dead on full if checked hot, but fluctuates when checked cool and almost always shows overfilled, especially as gets colder out.
So I check hot 90% of time.
Theres nothing wrong with checking it hot then noting the corresponding cold level and checking it cold using that revised mark.
Too much is made of the level. My trans shop said you should slightly overfill.
Too much is made of the level. My trans shop said you should slightly overfill.
MolaKule
Staff member
Originally Posted By: zach1900
Why do most car makers specify checking the ATF hot after a 20 mile drive or so and checking in park with engine idling, why don't they reference where the operating level is correct hot and then mark that on the dipstick so one could check it in the morning without having ever starting the car, I suppose I could check it hot like instructed then let it cool and mark that on the dipstick, not trying to sound paranoid but I do like checking the oil cold and would like the same for the ATF.
Because an oil expands in volume as the temperature rises.
Overfilling when cold results in foaming when hot. Aeriated oil due to Foaming doth not make a good lubricant.
Why do most car makers specify checking the ATF hot after a 20 mile drive or so and checking in park with engine idling, why don't they reference where the operating level is correct hot and then mark that on the dipstick so one could check it in the morning without having ever starting the car, I suppose I could check it hot like instructed then let it cool and mark that on the dipstick, not trying to sound paranoid but I do like checking the oil cold and would like the same for the ATF.
Because an oil expands in volume as the temperature rises.
Overfilling when cold results in foaming when hot. Aeriated oil due to Foaming doth not make a good lubricant.
MolaKule
Staff member
Originally Posted By: turtlevette
Theres nothing wrong with checking it hot then noting the corresponding cold level and checking it cold using that revised mark.
Too much is made of the level. My trans shop said you should slightly overfill.
You should find another transmission shop.
Theres nothing wrong with checking it hot then noting the corresponding cold level and checking it cold using that revised mark.
Too much is made of the level. My trans shop said you should slightly overfill.
You should find another transmission shop.
Originally Posted By: MolaKule
Originally Posted By: turtlevette
Theres nothing wrong with checking it hot then noting the corresponding cold level and checking it cold using that revised mark.
Too much is made of the level. My trans shop said you should slightly overfill.
You should find another transmission shop.
Better to have a little more than to suck air and starve a bearing.
Originally Posted By: turtlevette
Theres nothing wrong with checking it hot then noting the corresponding cold level and checking it cold using that revised mark.
Too much is made of the level. My trans shop said you should slightly overfill.
You should find another transmission shop.
Better to have a little more than to suck air and starve a bearing.
Originally Posted By: zach1900
I just realized my ATF dipstick does have a "cool" and "Hot" upper and lower factory markings, not sure what they mean by "cool" as in just starting an engine that's been sitting overnight or what, also the dipstick is dark colored as opposed to the oil dipstick which is shiny.
I am probably overthinking it as in 20 years of vehicles I have never had an ATF fluid fluctuate.
"Cool" is there to fill an empty trans, to get it about right... but still on the low side. Then you drive until thetrans is hot, and put the level right.
I just realized my ATF dipstick does have a "cool" and "Hot" upper and lower factory markings, not sure what they mean by "cool" as in just starting an engine that's been sitting overnight or what, also the dipstick is dark colored as opposed to the oil dipstick which is shiny.
I am probably overthinking it as in 20 years of vehicles I have never had an ATF fluid fluctuate.
"Cool" is there to fill an empty trans, to get it about right... but still on the low side. Then you drive until thetrans is hot, and put the level right.
Last edited:
MolaKule
Staff member
Originally Posted By: Jetronic
Originally Posted By: zach1900
I just realized my ATF dipstick does have a "cool" and "Hot" upper and lower factory markings, not sure what they mean by "cool" as in just starting an engine that's been sitting overnight or what, also the dipstick is dark colored as opposed to the oil dipstick which is shiny.
I am probably overthinking it as in 20 years of vehicles I have never had an ATF fluid fluctuate.
"Cool" is there to fill an empty trans, to get it about right... but still on the low side. Then you drive until thetrans is hot, and put the level right.
Jetronic
Originally Posted By: zach1900
I just realized my ATF dipstick does have a "cool" and "Hot" upper and lower factory markings, not sure what they mean by "cool" as in just starting an engine that's been sitting overnight or what, also the dipstick is dark colored as opposed to the oil dipstick which is shiny.
I am probably overthinking it as in 20 years of vehicles I have never had an ATF fluid fluctuate.
"Cool" is there to fill an empty trans, to get it about right... but still on the low side. Then you drive until thetrans is hot, and put the level right.
MolaKule
Staff member
Originally Posted By: turtlevette
Originally Posted By: MolaKule
Originally Posted By: turtlevette
Theres nothing wrong with checking it hot then noting the corresponding cold level and checking it cold using that revised mark.
Too much is made of the level. My trans shop said you should slightly overfill.
You should find another transmission shop.
Better to have a little more than to suck air and starve a bearing.
You are not going to starve a transmission bearing by having your ATF level 450 mL low.
Originally Posted By: MolaKule
Originally Posted By: turtlevette
Theres nothing wrong with checking it hot then noting the corresponding cold level and checking it cold using that revised mark.
Too much is made of the level. My trans shop said you should slightly overfill.
You should find another transmission shop.
Better to have a little more than to suck air and starve a bearing.
You are not going to starve a transmission bearing by having your ATF level 450 mL low.
Originally Posted By: JTK
Any time I do an ATF drain/fill, I do it at a ~62-75F ambient temp and I just add back the amount that came out.
I do the same. Using Mityvac to extract ATF in garage after overnight parking, pour back in the same amount plus few ounces.
Any time I do an ATF drain/fill, I do it at a ~62-75F ambient temp and I just add back the amount that came out.
I do the same. Using Mityvac to extract ATF in garage after overnight parking, pour back in the same amount plus few ounces.
Originally Posted By: MolaKule
Originally Posted By: turtlevette
Originally Posted By: MolaKule
Originally Posted By: turtlevette
Theres nothing wrong with checking it hot then noting the corresponding cold level and checking it cold using that revised mark.
Too much is made of the level. My trans shop said you should slightly overfill.
You should find another transmission shop.
Better to have a little more than to suck air and starve a bearing.
You are not going to starve a transmission bearing by having your ATF level 450 mL low.
Yea, I think the deal is the dipstick might be off and you'd be lower than that.
Originally Posted By: turtlevette
Originally Posted By: MolaKule
Originally Posted By: turtlevette
Theres nothing wrong with checking it hot then noting the corresponding cold level and checking it cold using that revised mark.
Too much is made of the level. My trans shop said you should slightly overfill.
You should find another transmission shop.
Better to have a little more than to suck air and starve a bearing.
You are not going to starve a transmission bearing by having your ATF level 450 mL low.
Yea, I think the deal is the dipstick might be off and you'd be lower than that.
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