Intriguingly, I still believe that transmissions are more complicated than engines. Sure, they both are home to a vast array of components and moving parts, all of which need to work in unison with one another. Yet, engines are relatively easy to work on and to access, whereas transmissions can prove exceedingly troublesome to even get to, let alone fix. Case in point, burnt transmission fluid.
As we all know, automotive gearboxes feature a myriad of gears, clutches, bands, solenoids, pumps, sensors, and whatnot. Most of these are mechanical in nature, and without some form of lubrication between them, the entire transmission would scrap itself in mere minutes. Hence, why all gearboxes have what’s known as transmission fluid (aka ‘gearbox oil’) in them to lubricate the innards.
Besides leaving behind a thin, slick, greasy film of lube, transmission fluid is also consequential to a gearbox’s function. By providing hydraulic pressure, transmission fluid ensures that certain parts of a gearbox could be actuated. For instance, using that pressure to shift gears around. But would all of this hold up when you have burnt transmission fluid circulating your car’s gearbox?
What Is Transmission Fluid, Anyway?
Before looking at burnt transmission fluid, let’s take a closer look at what this fluid typically does to your gearbox. So, what is transmission fluid, and what does it do? To put it in layman’s terms, it’s the equivalent to motor oil, but for your transmission. It’s a lubricating oil or greasy solution. When used to circulate freely in an enclosed transmission case, transmission fluid provides lubrication.
As it flows around, a thin film of oil is stuck onto the many moving parts of the transmission. It could allow those components in the gearbox that have to physically make contact grind, twist, turn, and so on without wearing them down. Consequently, expanding the lifespan of these components, and maintaining their performance, reliable operation, as well as efficiency in tip-top shape.
Otherwise, the bare metal pieces of your gearbox’s internals could easily grind each other down. On another note, transmission fluid also functions to cool these parts down. As it flows around inside of the transmission, gearbox oil absorbs heat wherever it goes. Before finally, flowing that hot gearbox fluid to the transmission fluid pan-slash-reservoir (or a dedicated oil cooler) to cool it down.
In addition, and this applies primarily to automatic gearboxes, transmission fluid is the sole provider of hydraulic pressure. Gearbox oil can easily be pressurized, before using that pressure to actuate or engage parts of the (automatic) transmission. For example, using that built-up pressure to force the torque converter to shift and change gears. This isn’t necessary for manually-operated gearboxes.
What Are The Different Types Of Gearbox Oil?
Despite how simple its operations are, they’re not all the same. This will be crucial to learn as we try to understand more about burnt transmission fluid. There is a wide variety of transmission fluids out there, varying in mixture and composition. Just like engine oil then, you can’t simply pick out a bottle of transmission fluid, and expect it to work right away with your car:
- Automatic Transmission Fluid – Also known as ‘ATF’, these are made, as their name implies, for auto gearboxes. However, more recent and modern manual transmissions are also compatible with ATF. They aid in providing lubrication, cooling, as well as hydraulic pressure. On the latter, it’s especially necessary for the operation of the torque converter, valve body, and clutch friction plate.
- Manual Transmission Fluid – Dedicated and specialized manual transmission fluid is only applicable with older cars (with manual gearboxes). For example, pretty heavy and viscous 75W to 140W (W is for ‘weight’ when it reaches temperature) is almost never used in modern manual cars. These days, if you have a (modern) manual car, you could easily interchange it with automatic-based ATF.
- Dexron, Mercon, ATF+ – They’re the most commonly used and popular ATF batch today. You’ll find it with most cars made by GM, Ford, Chrysler, Honda (and Acura), Jeep, Hyundai, Toyota (and Lexus), and more.
- HFM – It stands for ‘high friction modified‘, which contains high quantities of friction additives (more on that later).
- Type-F – Last used in the 1970s, you won’t be using this unless you have a classic car (with a bronze clutch plate).
- CVT Fluid – Made specifically for ‘continuously variable transmission‘, where pulleys and chains are used instead of gears.
- Hypoid Gear Oil – Incredibly resistant to high temperatures and pressure, you’ll normally find them in the rear axle of heavy trucks.
What Is Synthetic Gearbox Oil?
Traditionally, conventional transmission fluid is refined from crude oil. Although easier and cheaper, they do come with flaws, such as carrying over impurities from crude, as well as limitations in their chemical compound. On the other hand, synthetic transmission fluids are specially made and mixed in laboratories, through careful chemical synthesis. The latter type is usually more expensive.
Aside from that though, synthetic fluids are beneficial in many ways. For instance, synthetic fluids could be synthesized with additives, as we hinted at earlier. These additives could provide additional properties to transmission fluids, such as improving their resistance to heat and pressure. Or, make them less prone to breaking down over time, improve their lubrication, or even add rust prevention.
Note, not all transmissions are compatible with synthetic-type fluids. But if they are, among the pros for opting synthetic over conventional transmission fluids include:
- It’s engineered to meet viscosity levels more accurately, which could improve lubrication. And, it can even enhance your fuel economy, by optimizing the gearbox’s efficiency and performance.
- Owing to its ability to sustain viscosity, lubrication, hydraulic pressure, and cooling properties even at higher temperatures and loads for long periods, you could expect it to shift more smoothly.
- They don’t require changing as often as conventional fluids. Lower maintenance comes with reduced costs over time to servicing and greater convenience.
- It’s incredibly resistant (by 3x as much compared to conventional fluids) to oxidation and thermal degradation. Thus, preventing a build-up of sludge, carbon deposits, and other impurities.
- Since your transmission can run cooler, smoother, and cleaner, you could possibly extend its lifespan, too.
- With special additives to combat corrosion in place, it can significantly reduce the chances of rust forming within the transmission.
What Causes Burnt Transmission Fluid?
Alas, and no matter how top-notch your gearbox oil is, unburnt transmission fluid is inevitable. With enough time, wear, and heat, every transmission fluid will eventually break its chemical compounds down. This is what causes burnt transmission fluid. In particular, here are some of the most common causes for why your gearbox oil is burning or emits a noticeably burning smell:
- Overheating transmission, which puts a lot of heat and strain onto the transmission fluid. Should it not be cooled for some time, it’ll start wearing down the fluid’s chemical mixture. If you’re used to putting a significant load on the transmission, installing a transmission cooler is a great idea.
- Driving with a low amount of transmission fluid (likely caused by a leak). In doing so, what little fluid is present will be overstressed, and has to work a lot to maintain lubrication, pressure, and cooling.
- Not having flushed or changed the transmission fluid in a long time. Gradually, gearbox fluid wears out, as the old and sludgy oil is unable to sustain the right lubricating or cooling properties.
- Heavy loads are put on it from driving, such as going off-roading, towing heavy trailers, or fast driving on the track. This not only puts more strain on the gearbox, but you’re also running it at higher temperatures. Therefore, you risk overheating it more frequently.
- Bad solenoids and faulty transmission components, especially within automatic gearboxes. Here, a solenoid is used to control the flow of gearbox oil. If that solenoid were to fail, it might not be able to circulate oil to certain parts of the transmission, starving it out, and wearing it down.
What Are The Symptoms Of Burnt Transmission Fluid?
In the first fleeting instance that you notice burnt transmission fluid, you should take prompt action. If left unresolved, burnt transmission fluid can seriously impact a gearbox’s driveability and function. Not to mention, putting substantially more strain and acceleration wear on the transmission, to the point of necessitating pricey gearbox repairs down the line. So, be wary for symptoms like:
- A burning odor, strong or otherwise, emanating from the interior. Specifically, close to the center console, leading to the engine. That’s where most transmissions are located. If it smells burnt, then your transmission has likely overheated, which could be caused by old and worn fluids.
- Transmission fluid might leak, or you might notice a low level of fluids in the reservoir. As a gearbox is a fully enclosed system, fluids shouldn’t leak or burn out naturally. If it’s leaking, see if the gearbox oil is bright red, and has a sweet smell. If it’s black or dark brown and has a smoky scent, then it’s burnt.
- Difficulties changing gears, or it’ll shift gears roughly. Have you noticed the gearbox hesitating when changing from one gear to another, or outright refusing them? You’ll notice other symptoms such as the transmission slipping in and out of gears, or shuddering constantly while you’re driving.
- If worse comes to worst, and you allow your transmission to get uncomfortably heaty, it might start smoking. At this point, your transmission fluids are no longer capable of cooling it down. If it’s smoke that you’re seeing, you shouldn’t be driving your car anywhere.
- In most modern cars, there are warning lights that could alert you of low or bad transmission fluid. Just be on the lookout for it on the dashboard. On some vehicles, transmission-related issues would otherwise trigger the check engine light.
How Can You Solve Burnt Transmission Fluid?
If your car has an issue with burnt transmission fluid with that smoky smell to it, then the only fix would be to replace it. There is quite a vast variance in how long transmission fluids are made to last. The low end of the spectrum would be once every 30,000 miles. Although, this is unusually low, and it’s usually the case if you use cheap transmission oil, or regularly overwork and heat up the gearbox.
For most vehicles, you can expect the lifespan of transmission fluids to be around 60,000 to 100,000 miles between fluid changes. Some higher quality fluids, such as specialty synthetic gearbox oils, are rated up to 150,000 miles before a change is necessary. In all, it’s best to refer to a technician that’s familiar with your car, your driving style, the gearbox it uses, and your choice of transmission fluid.
You should also consult the local mechanic or gearbox specialist about what needs to be done to fix your burnt transmission fluid issue. In most instances, it’s sufficient to simply drain out the old, burnt transmission fluid. Before then refilling it with a fresh bottle. Primarily, it’ll depend on how long it’s been since the last transmission fluid change, and whether the old fluids have caused wear within.
However, in the worst-case scenario, you might be recommended to do a full transmission fluid flush instead. A flush shouldn’t be the default choice in every situation, mind you. There are cases where a flush could actually prompt issues to appear on an otherwise good gearbox. For example, causing a gear slippage where it wasn’t present before. Therefore, it’s best to ask a technician.
Frequently Asked Questions On Burnt Transmission Fluid
Here’s a quick roundup of some of the most pressing concerns in regards to burnt transmission fluid, and how it affects you…
1. What Color Should Transmission Fluid Be?
When it’s fresh and poured straight from a new bottle, transmission fluid should be bright red, with almost a syrupy look to it. And, it maintains a transparent consistency. But given time, it’ll start to change colors and opaqueness.
You could always refer to the color of your transmission fluid as a gauge to see just how well the transmission is doing. Or, if you need to get that gearbox oil changed:
- Reddish-Brown, Semi-Transparent – It’s still in good condition, but slightly worn in compared to a fresh batch.
- Brown, Slightly Opaque – At this stage, it’s getting a bit old, worn, and dirty. You’re recommended to have the fluid changed at this point, as well as swapping out the transmission fluid filter.
- Blackish-Brown, Very Opaque – Not only is it old and dirty, but there could be traces of oxidation and significant quantities of contaminants in the fluid. This is what we’d call a very burnt transmission fluid, and should be changed ASAP.
- Light Pink, Milky – If it looks like a strawberry milkshake, then it’s a very bad sign. It denotes that water or coolant has somehow leaked into the transmission fluid, and is now circulating the gearbox. Not only do you have to replace this contaminated fluid. But, depending on how bad the damage is, you might have to rebuild, restore, or replace the entire transmission.
2. How Much Does It Cost For A Fluid Change?
If you’re getting it changed, a drain and fill with burnt transmission fluid costs you around $100 on average. If you’re getting it done at a dealership or a transmission specialist, there might be a slight premium to that. So, roughly $150 or thereabouts. This price is only for a change, though.
Should you require a fluid flush (only in acute and specific situations), it’ll cost you at least $150. At dealerships or specialty technicians, you can expect that to rise closer to around $200 to $250. We also have to take into account the cost of a new fluid filter, which should be around $15 to $30.
When it requires you to replace the worn-out seals and gaskets around the transmission fluid pan, you might consider adding another $75 to $150 to the total bill. But if you’re handy with a car, you could save on labor fees by doing it DIY. A new bottle of gearbox oil costs about $50.
3. Is Burnt Or Worn-Out Transmission Fluid Serious?
In a word, yes. Transmission fluid is the only thing keeping your gearbox from scrapping itself to bits. Should it be burnt or is worn out, that gearbox oil can’t maintain a sufficient amount of lubrication, cooling, as well as compromising on hydraulic pressure that’s essential for automatics.
In other words, this means that your gearbox will run hotter, poorly, with reduced performance and terribly driveability, as well as wearing itself down. Over time, burnt transmission fluid will begin to manifest into causing substantial issues with your transmission.
If you’re sensing the early symptoms of burnt transmission fluid, the best thing you can do would be to get it changed, right away. Delay for any longer, and leave those burnt oils circulating in the gearbox, it will break it altogether. Hence, requiring an extensive rebuild or replacement.
At that point, the entire transmission has to be reconditioned from scratch. Key components will be replaced, like the rest of the gearbox will be machined and restored. Instead of a $100 or so gearbox fluid change, you’re now looking at an invoice of around $1,000 to upwards of $4,000 or more.
4. Can You Manage A DIY Fluid Change?
While it’s much cheaper to do it yourself rather than relying on a mechanic, it’s not always a good idea to DIY a transmission fluid change. That’s especially so with old, dirty, rusty, burnt, and what’s likely contaminated gearbox oil. This is the case for a few key reasons:
- A thorough diagnosis has to be performed by skilled technicians. In particular, they’ll have to discuss and decide whether a simple drain-and-fill will be enough to solve your problems. Or, if a fluid flush and other extensive gearbox repairs ought to be necessary.
- You can’t simply use just any transmission fluid. Yes, you may refer to the owner’s manual for a list of what oils are compatible with your car. Yet, it’s still best to consult with an experienced and skilled mechanic, who knows instantly what fluids would be best suited to you.
- Owing to the tight tolerances inside of a gearbox, even draining it will require some skill that most regular folks lack. For instance, old and dirty transmission fluids might get stuck in place on certain parts, stubbornly refusing to drain out. Or, there could be thick sludge in there that’s clogged it up.
- It would be wise, especially in more serious cases of burnt transmission fluid, to inspect the rest of the gearbox in detail. For example, taking the entire gearbox apart, and checking every little nook and cranny to ensure that it hasn’t caused any damage or wear inside the transmission.
- Unlike changing or topping up your engine oil, transmission fluid is much more complex. Unless you have some mechanical skill, experience, and know-how, a DIY fluid change here isn’t recommended. One seemingly simple mistake, and you may end up breaking the gearbox as a whole.
Final Thoughts On Burnt Transmission Fluid
Well then, that just about wraps up our look at burnt transmission fluid. Although this isn’t an issue that’ll impact most people, it may eventually occur if you haven’t been diligent with regular servicing and maintenance. Changing the gearbox oil every so often is a great preventive measure to help prevent you from needing to worry about burnt transmission fluid, and what damage it can cause.
But should you be experiencing burnt and worn transmission fluid, stop your car, and don’t even think about driving it. Continuous load, heat, and pressure will no doubt worsen the condition of the already dirty and burnt-out transmission fluid. In doing so, you’re putting your entire gearbox at risk of failure or permanent scarring. The latter would cost you far more than a simple gearbox fluid change.
Why pay thousands for an extensive gearbox rebuild when a straightforward fluid change will cost you merely $100 or so? Not only that, but fluid changes will only take a tiny bit of your time, and it’s not as punishing to your stress level. So, be attentive to the intervals between your last fluid change, and keep on top of regular services. A small reminder like this could be a lifesaver.
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