Part 2… This is very long but with a lot of good info…
Disclaimer: The terms transmission, transaxle, and trans are used interchangeably here and refer to multi-speed automatic transmissions & CVT’s to a point…
First, there is really no such thing as a truly “sealed” transmission… What most people call sealed transmissions are simply dipstickless transmissions… Likewise, there is no such thing as “lifetime fluid”… There is only fluid that is expected to last for the anticipated service life of the transmission, which manufacturers generally consider to be around 150,000 miles… Many transmissions can and do last much longer than that…
Dipstickless transmissions have been around for over 30 years, so they are nothing new… As a former transmission builder who still dabbles in the trade, I understand why manufacturers and many builders prefer them…
When serviced correctly, a dipstickless transmission is filled to the exact fluid level the engineers intended… A traditional dipstick-equipped transmission can easily be overfilled or underfilled, both of which can cause problems… Eliminating the dipstick also reduces the chances of someone introducing the wrong fluid into the transmission…
I know most people dislike dipstickless transmissions, but in many ways they are a better design because the average vehicle owner simply doesn’t know much about vehicle maintenance… I’ve seen people put engine oil in the brake master cylinder, use the wrong engine oil, add the wrong ATF to a transmission, and overfill or underfill components… I’ve seen some things that would make you wonder how the vehicle survived at all…
Most people also don’t realize that many automatic transmissions require the engine to be running to properly check the fluid level… Some older designs, such as certain Hondas, have different procedures, but many modern automatics do not…
As someone who has professionally built transmissions, I’d rather the average customer not be able to tamper with the transmission while it’s under warranty, and I’m sure the manufactures are the same way…
Transmission fluid expands significantly with temperature, which is why many modern transmissions must be checked within a specific temperature range…
Is it a bit of a pain? Absolutely. Is it a better and safer way to ensure the correct fluid level? In my opinion, yes…
Manufacturers have also extended service intervals over the years while maintaining reliability… We used to service transmissions every 30,000 miles or less, later, some moved to 50,000-mile intervals, and then came the unrealistic “lifetime fluid” marketing… Even experienced master technicians, such as the Toyota/Lexus specialist commonly known as the Car Care Nut, recommend servicing Toyota’s ATF WS transmissions approximately every 60,000 miles rather than following the lifetime-fluid philosophy…
Much of this is possible because modern ATFs are better formulated, friction materials have improved, and transmission temperature management is far more controlled… Today’s transmissions warm up faster and maintain operating temperature more effectively than older designs…
On modern transmissions, there is nothing wrong with performing a pan drop and filter replacement, if it has one… However, on Toyota’s dipstickless transmissions using ATF WS and others, regular drain-and-fill services are generally sufficient and are recommended for a reason… If the transmission has a serviceable filter and removable pan, then perhaps every 100,000 to 120,000 miles a pan drop and filter service makes sense, or anytime the pan gasket needs replacement because of a leak… After all, a transmission pan is simply another potential leak point…
Generally speaking, on modern transmissions, being off by even a few ounces can matter, as a few ounces may already place the fluid level outside the engineers intended specification, and being off by half a quart or more should be corrected as soon as possible…
Some owners have reported improved shift quality after correcting fluid level, even when only a small amount of fluid was added or removed… Low fluid levels can lead to delayed engagement, slipping, or erratic shifting because of reduced hydraulic pressure, overfilling can cause the fluid to aerate or foam, which also reduces effective hydraulic pressure and can result in similar symptoms, increased heat, and possible seal damage…
These late-model transmissions rely on very precise hydraulic pressure and fluid control for proper operation… Just because a transmission seems to work fine today doesn’t mean there won’t be long-term consequences… Operating with an incorrect fluid level can accelerate wear and shorten transmission life over time…
Universal ATF is spec’d for a multitude of transmissions, and just because it has all the manufactures recommended additives in it for your transmission, doesn’t mean those other universal additives for other manufactures are compatible with the clutch fibers and solenoids and what nots of your trans… ATF is very critical in these modern transmissions and so that means that the other manufactures additives may not be correct for it… One of the reasons for premature transmission failure is using the wrong ATF (that includes universal ATF)…
Even the car care nut says that using universal ATF has damaged Toyota transmissions…