Wrench Tip: How To Make Diff Oil Changes Easier

Wrench Tip: How To Make Diff Oil Changes Easier

by David Zipf

Fluid changes are a necessary evil of owning a car.  Of all the different fluids in a modern car, changing differential oil is probably my least favorite.  You're stuck underneath working above your head, killing your arms.  More often than not, you're working in cramped quarters.  And then there's the oil itself.  It's slimy, sticks to absolutely everything, and worst of all it stinks horribly.  I knew my VehiCross would need new oil in its diffs, but the local shops wanted $200 to flush both axles.  Screw that.  I'll do this myself.  In a parking lot.  In 45 degree weather.

Diff oil is much heavier than engine oil.  And you have to pump it uphill into the diff (the Vehicross, like most other cars and trucks, doesn't have enough room to turn the bottle sideways and pour the oil in).  The VehiCross requires 2.5 quarts of 90W-140 oil in its rear axle.  Now when it's 45 degrees outside, 90W-140 turns into sludge.  After spending an hour pumping the first quart of oil into my rear axle, and breaking a hand pump in half in the process, I decided there had to be a better way.

Heating up the oil will thin it out and make it much easier to pump into the diff.  But how do you heat up the bottle, especially in an apartment?  The microwave seems like a safe bet.


Well that's not going to work…

Ok, what about the oven?  It is big enough, but even at its lowest setting, the oven will heat the oil to the point that it will start to break down, making it useless in your diff.  On top of that, the hot rack will melt the bottle making a big mess.  How about the stove?  The lowest setting won't overheat the oil, but that burner will still melt the bottom of the bottle.

I have that covered.  Back in the day, I was a BoyScout and our Troop would camp in the wintertime.  One of our tricks to staying warm was to heat up a nearly full lexan water bottle in a pot of water and stick it in the foot of our sleeping bags.  The warm bottle would keep our feet warm until we fell asleep and when we woke up we would have liquid water to drink.  We used a pot of water to heat the bottle because a bare pan would melt the bottle.  But the water in the pot would transfer the heat evenly to the bottle, while preventing the bottle itself from melting.

My Scoutmaster would be proud.  Gordon Ramsey would call me a shithead.

Before you piss off anyone else you might be living with, you should probably use an old pot nobody cares about (this pot was inherited from old roommates and is rusting.  Useless for cooking, but perfect for simmering diff oil).  Put the stove on its lowest setting and let the bottles simmer for about 10 minutes.  The water should be warm, but cool enough to put your hand in.  By keeping the heat low, you will thin the oil enough to pump, but not enough to break it down.  Make sure you remove the safety seal of the bottles and leave the caps loose to allow for expansion.  It took me over three hours to change my rear diff's oil.  Using this trick, it only took about 45 minutes to do the front.  Admittedly the front has a quart less capacity and uses thinner oil (the 80W-90 you see in the pics above), but even the 90W-140 heated up was much, much easier to pump into the diff.  If you fire up your oil water bath just after you've jacked your car up, it should be ready by the time you drain the diff and get it ready to be refilled.

Never changing your diff oil, like the previous owners of my VehiCross did, does an even better job of thinning out your oil.  This old oil was as thin as water, despite the chilly weather, and it was about 60,000 miles past due for changing.  No wonder my drivetrain was groaning…

Leave a Reply

Your email address will not be published. Required fields are marked *