There are, in general, three types of vehicle transmission: manual, automatic, and CVT. Good old manuals are the ones where you choose the gears on your own and have to do a lot of fancy work with a clutch pedal and shifter. Automatics take most of that work (and fun) out of the equation for you and do all their own shifting using what I can only describe as hydraulic sorcery. CVTs, or Constantly Variable Transmissions, are a type of automatic transmission that uses a bunch of drums, pulleys, and either a belt or chain — as opposed to the physical gears used in manuals and automatics — to get an engine’s power to the rear wheels.
Each of these transmission types has its pros and cons. Some of these are real actual pros and cons, others are purely vibes-based and are hashed out ad infinitum on enthusiast forums and in the comments of blog posts all across the internet. Each kind of transmission has its place, and each one goes about its job in its own fascinating way. Each one also runs on a bespoke lubricant that can’t (or, well, shouldn’t) be used in the others.
What happens, though, if you use CVT fluid in a manual, or regular old ATF in a CVT? Well, that depends on the transmission and the fluid involved.
What is transmission fluid, anyway?
First off, let’s talk about what transmission fluid does for your transmission. Transmission fluid is a lubricant; it keeps all the spinning, whirling, meshing metal bits inside the transmission running smoothly and prevents premature wear and tear. It also acts as a coolant and keeps temperatures down as it absorbs the heat of all that gear friction. Finally, it absorbs the shocks of changing gears and smooths everything out. Running low on transmission fluid — or, heaven forbid, running out — can destroy a transmission in a relatively short amount of time.
As there are three general types of transmission, there are three general types of transmission fluid. Manual trans fluid, or gear oil, is thick, heavyweight oil — typically anywhere from 75W to 140W depending on the application — and stinks like crazy. Especially when it’s old or burnt. Automatic transmission fluid, or ATF, is thinner and typically full of additives and detergents to keep the insides of an automatic transmission clean and fresh. It’s usually blood red, although green ATF isn’t unheard of. CVT fluid is a high-tech, advanced petroleum product that, like regular ATF, is full of all kinds of special additives. The most important of these is the friction modifiers that allow the CVT’s belt to grab onto the various drums and pulleys.
What’s the worst that can happen?
Mixing up your transmission fluids is bad news, and the symptoms mimic those of a dying transmission (which should give you some indication of how bad this is). These symptoms include difficulty shifting gears, rough shifting, gear slippage, whole gears just disappearing, stalling after changing gears, and a general cacophony of banging, clanging, and grinding. A transmission with the wrong lubricant inside is also more prone to overheating, which just exacerbates all the other problems happening while the transmission starts to eat itself.
So, what should you do if this happens? Drain that transmission and replace the fluid with the correct fluid pronto. Failure to change the fluid out for the right mix can lead to catastrophic damage to your transmission. Do it yourself or take it to a shop, but do it as soon as possible or you could be looking at a whole new transmission instead of just a few bucks in trans fluid or a couple hours wasted in a mechanic’s waiting room.