Regardless of some car manufacturer’s claims that their differential fluid lasts the vehicle’s lifetime, it’s good practice to change your car or truck’s differential fluid every 30,000-60,000 miles, or even much sooner if you use your vehicle to tow heavy loads or for racing. You can bet your vehicle manufacturer uses diff fluid that outlives your warranty, that’s for sure. But, after your warranty expires, they don’t really mind if you run into heavy repair costs ;). Any serious mechanic will tell you “lifetime fluids” don’t exist, and periodic fluid changes are the smart thing to do if you want to avoid expensive repair bills.
The reason why is that your differential and its fluid is under extreme loads. The diff fluid has to keep your differential bearing and pinion gear lubricated and cool, and protect the internals against corrosion.
As the fluid gets older and contaminated, its protective properties diminish fast, leaving your differential’s components vulnerable to corrosion and accelerated wear. Over time this wear will result in gear whine and eventually failure, leading to expensive repairs.
Yet, differential fluid isn’t expensive and no special tools or skills are required. You can do a fluid change yourself easily. It only takes up to an hour and you won’t have to pay a mechanic to do it for you.
Check out “Best Differential Fluids” for more information on dedicated differential fluids. We’ve listed the best ones in a comprehensive review.
Here’s how to change your differential fluid:
In order to fill your differential fluid to the right level, your vehicle needs to be on a level surface. If it isn’t, you’ll under- or overfill your differential, which can lead to mechanical problems.
If your vehicle has high ground clearance, like a large SUV or a Heavy-Duty pickup truck, your differential is easily accessible. If it’s not, jack it up so the diff is accessible and put jack stands underneath for safety. Double-check for stability and safety before going underneath.
If you have access to a car lift or inspection pit, it’s even easier to reach your vehicle’s differential, of course.
Although you don’t plan to make a mess, chances are you will (ask Murphy). Put a tarp or some plastic sheeting underneath your differential just in case things go wrong. Better safe than sorry!
Put an oil pan or a wide container that is large enough to catch at least 5 quarts of oil underneath your differential.
First check if the diff fill plug comes loose before draining your differential. Because if it doesn’t, you won’t be able to refill it. For most US vehicles you’ll need a 3/8″ or a 1/2″ male square socket size or a 8mm and 14mm hex. On foreign cars you’ll often find 22mm and 24mm socket sizes or hex sockets. Drain/fill plug socket sets are available that fit most common sizes. Make sure that your socket fits snugly before applying force and be very careful not to damage the filler plug. If you do, it’ll be very hard to ever get it loose.
If you’re confident that you can get it out, leave the fill plug in place for now to prevent debris falling in the fill hole.
If your car differential has a drain plug, (not all vehicles have one) it should be situated at the lowest end of your differential.
You can also drain the fluid as if there was no drain plug (see below). Although it’s more work, you’ll be sure that all the contaminants are gone and you’ll be able to visually inspect your differential gears.
If your car differential only has a fill plug but no drain plug, you’ll have to undo the differential cover.
If you’ve only removed your differential’s drain plug to drain the fluid:
However, if the magnet is loaded with larger, chunky metal parts, something ain’t right and you need to visually check your differential’s gears by opening the cover to see if any teeth are damaged. Have a professional look at it if they are.
Don’t worry about fine paste-like iron shavings, they come from normal wear. In some cases the whole magnet is coated in a thick paste of grayish metal shavings. Squish the paste between your fingers (wearing nitrile gloves of course). If the paste is very fine, it’s perfectly normal and you need not worry.
If you’ve removed the differential cover, you’ll need to reinstall it:
If there’s a drain plug magnet on the inside of the diff cover, clean it thoroughly and make sure all metal shavings have been removed.
Tighten the cover in two passes: first go ‘round at about half torque and then do a second pass at full torque. That’s it, your diff cover is back in place.
That’s all there’s to it. Wait for the RTV to cure for 24 hours before adding differential fluid (check product instructions).
Now that everything is clean, sealed and back in place, it’s time to fill the differential with clean, fresh fluid. The easiest way to do this is to use a simple manual fluid pump.
You could put some RTV on its thread but for the filler plug, that’s not strictly necessary. Be careful not to over-tighten it.
You’re done! Great job!
Your differential is well-lubricated and safe from corrosion for years to come!
Frank is a true DIYer and car enthusiast with over three decades of hands-on experience. He's mastered everything from classic car restoration and detailing to drafting renovation blueprints and construction. With a penchant for tools and home improvement, he's constantly enhancing his house and garden. In his garage, his passions merge as he meticulously maintains and refines his beloved cars. Seeking to channel his vast DIY knowledge and professional experience in product analysis and trade, he founded this site. Offering readers invaluable insights to maximize value and achieve project success, Frank ensures you get the real deal in a world full of hyped-up products and sneaky paid promos.
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