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Hope this helps.
Part 1 -- checking when engine is running, transmission in Park, all as described in the owner's manual.
Okay, we all know that fluid expands when warm -- that's why the dipstick has two scales, one for each of two sample temperatures. It's generally considered that this should be the most accurate way of determined your proper fluid level, but...!
The 'but' is that you need to know your fluid's temperature to use one or the other scales, and that's hard to know for sure! In fact, I've got one of those infra-red RayTek remote thermometers (which is pretty accurate, by the way, as checked against my very expensive lab equipment -- I'm a biology professor, by the way), and by reaching under the car and putting the RayTek up against the sump pan of the transmission, I think I'm getting a pretty darn good reading of the fluid's average temperature.
What's important, however, is that you would be pretty surprised at the temperatures. Forget all the guidelines (and I mean *all*) about driving for 15 or 30 minutes to warm up the fluid to 90 deg C (the hotter scale, as I recall) -- rubbish! In the summer, you can drive all day at highway speeds and maybe just barely hit 70 deg. C. -- unless, I suppose, you've got some sort of transmission problem or you're towing a trailer. In the winter (at least here in the N.E. this year, it's even more surprising -- low! You can just get it up to 50 deg. C.
When your car is cold (you've started the engine but you haven't started driving the car yet), particularly N.E. cold right now parked outdoors, the fluid probably should be somewhat below the add mark of the lower temperature scale on the dipstick, maybe even off the dipstick (depending on how cold), but after you've been driving around a while, having it reach a temperature suitable for the lower temperature scale is reasonable as a rough guess.
What's dangerous, however, is the risk of overfilling -- overfilling is generally considered to be a more damaging condition than modest underfilling, so be sure to add fluid only enough to err on the side of underfilling, and avoid the possibility of overfilling!
Anyway, if you can get a RayTek or similar unit, then at least you could interpolate between the two scales (sides of the dipstick) and get an accurate determination of your proper fluid level -- knowing the temperature is the only way to be accurate! Other than that, you can only get a "ballpark" idea of what the fluid should be, somewhere between the middle of the two scales after you've driven for a while -- quite a while, and at higher speeds, in this winter weather.
Part 2 -- there's another way to check the fluid, without temperature info.
This is an undocumented method -- but I've found it to work, verified against the aforementioned temperature-dependent method. But you generally don't need to know the exact temperature, only that's it's either winter or summer.
Look carefully at the dipstick -- particularly the metal part above the plastic tip. You should see a long, rectangular slot cut out of the side or edge of the dipstick an inch or so above the plastic tip. Now follow these directions carefully!
Let the car sit overnight. The next morning, do NOT start the engine -- the fluid in the transmission must not only be cold (equilibrium with the ambient air temperature) but also undisturbed by circulating through the transmission!
Open the hood, and withdraw the dipstick and wipe it properly (lint-free rag, etc.). Chances are, you didn't find any fluid on the dipstick anyway -- that's normal. Now reinsert the dipstick and after a pause, withdraw it again and this time examine the fluid level on the dipstick. This time the level should show, and it should be up and hopefully somewhere within the range of the long, rectangular slot that you took note of earlier....
(the fluid doesn't show on the dipstick until it's been withdrawn once -- this is normal)
.... in winter, it's best if the fluid is at the bottom of the slot; in summer, at the top of the slot (and in spring and fall, in the middle). But it should *never* be above or below the slot.
If it's below the slot, add some, but only a little at a time! Unless you've got a vacuum device to suck ATF up through the dipstick tube (boating stores have these, for oil changes on inboard engines, by the way), you don't want to risk overfilling as I noted earlier!
Remember, that this reading was done before you first started the car in the morning -- the engine hasn't been running for many hours.
The reason this works is that (I believe) this slot is provided to measure the fluid level when the cars are in a storage depot, either at the factory or the shipping area, when starting every car and warming them up is impractical. I don't know this for sure, of course (Volvo hasn't taken me into their confidence :-), but it seems to work for me -- and I've got a very accurate method of measuring the fluid level because I can determine the fluid temperature.
By the way, if you want to buy the RayTek, it's available at many catalog sources, including IPD and Griot's Garage, for about $80 +/- a bit. It's useful for all sorts of things.
Good luck.
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