Dear Tom and Ray:

The owner's manual for my 2010 Honda CR-V with all-wheel drive states that only Honda fluids may be used in the car, except for motor oil. The dealer's service department confirms this. The rear differential gear oil, automatic-transmission fluid, power-steering fluid, brake fluid, engine coolant, etc., have to come from Honda, they say. Dire and catastrophic results are promised otherwise. I think "hellfire and brimstone" is in there somewhere, too. Is there a chance that Honda is overdramatizing this as a way to provide extra revenue to the dealer?

-- Stan

TOM: What the manufacturers tell us is that it's all about corrosion, Stan. Honda, and other carmakers, use different alloys of aluminum in their components -- mostly to make their vehicles lighter and more fuel-efficient.

RAY: And they say that their own fluids are designed to minimize corrosion in those specific kinds of aluminum over time.

TOM: Is it possible that they also enjoy a little extra profit by selling their own fluids? Sure. Is it possible that they benefit from having a lot of customers return to their dealerships for service so they can sell them other services and a 2015 Odyssey? Sure.

RAY: But they also may be absolutely right about their fluids minimizing corrosion on their own cars. And it's in their long-term interest to not have key components of their cars corrode and fail as they get older.

TOM: Keep in mind that just because you want to use Honda fluids, you don't have to go to the Honda dealer for service. You can ask your independent shop to use Honda fluids, and it'll get the stuff from the dealer.

RAY: We have an independent shop, and -- with the exception of motor oil -- we actually use nothing but Honda fluids on all late-model Hondas. The difference in cost is pretty minimal. And we figure, why risk a part that costs thousands of dollars to replace in order to save a few bucks on fluid? Especially with something like the differential oil, which gets changed only every 30,000 miles. Or the transmission fluid, which is changed even less frequently.

TOM: The only downside (and it's for us, not you) is that as more and more manufacturers demand that only their own fluids be used, we need more and more shelves in the garage to warehouse all that stuff.

RAY: We had to practically buy out IKEA last year. Then we had to go back a week later and buy one more shelving unit to store all those Allen wrenches.

TOM: So we don't have proof that using Honda fluids is absolutely necessary, Stan. But we think it's a reasonable thing to do based on Honda's claims. That's what we do for Honda owners who come into our shop.