Certain Cars May Require More Diligent Maintenance

Dear Car Talk:

I have a Honda CR-V with all-wheel-drive. I'm curious about how frequently I have to change the rear differential oil. The automatic maintenance reminder that pops up on my dashboard has recommended this service three times in 60,000 miles.

That's obviously not as often as engine oil, yet the differential stays cool, has no combustion gasses mixing in, and I never go off road (other than to the Trader Joe's parking lot, your joke).

Is this a profit center for the dealer? There is indeed a good lake nearby for boating. -- Bill

If you had a different car, Bill, I would suspect that your dealer has a boat payment coming due. But Honda CR-Vs do require unusually frequent rear differential fluid changes. I don't know why -- probably an engineering flaw of some kind -- but the differential fluid in CR-Vs does degrade faster than in other cars we work on. And eventually, when it degrades enough, it creates a "chattering" sensation when you make sharp turns -- as if one wheel is grabbing, which it is.

So far, we haven't seen any permanent damage done by this. As soon as we change the differential fluid, the chattering goes away and appears to stay away. But I suspect it's better to change the fluid before the chattering starts.

How often should you change it? Every 20,000 miles, like your service light suggests? I don't have the research (or the automotive physics lab) to answer that question precisely. But the CR-Vs we see in the shop that are chattering generally have 30,000-60,000 miles on them. So, do I think you'll be visited in your sleep by the ghost of "differential replacements future" if you did it every 30,000 miles instead of every 20,000? Probably not.

But if you like to be meticulous about your maintenance, and plan to keep the CR-V forever, then change the fluid when it's recommended. It certainly can't hurt.

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