Just because fluids are dirty it doesn't necessarily mean they need to be replaced.
Dear Tom and Ray:
I recently took my 1999 Dodge Ram 1500 conversion van in for an oil change. The shop did a full-service check of all my fluids and put a sample of each on a plastic card to compare the colors with those of brand-new fluids. The mechanic said that my differential and power-steering fluids are dirty (dark) and should be changed -- for $79.95 each. I thought I read in one of your columns that the differential oil rarely, if ever, needs to be changed. And it seems to me that $79.95 is a lot for these services. I only have 19,000 miles on the van. What do you think? -- Scott
TOM: I'm going to guess that he was wearing a top hat, Scott. Because he's giving you a good old-fashioned song and dance. And an expensive one, at that.
RAY: Of course the fluids are dirty. They've been doing their jobs for 19,000 miles. But that doesn't mean they need to be replaced.
TOM: In the old days, when cars used to last only 100,000 miles, we would never change the differential fluid. Now that cars are lasting longer and some of them have more complicated differentials (with limited slip, for instance), we wouldn't argue with changing it at some point. For instance, if your car is still humming along between 60,000 and 90,000 miles, and you plan to keep it forever, I could see changing the differential fluid then.
RAY: Same with the power-steering fluid. Most cars you find in the junkyard have their original power-steering fluid. Usually, a hose will blow long before the fluid ever goes bad. But again, with today's expensive rack-and-pinion systems, I wouldn't argue with changing the power-steering fluid somewhere between 60,000 and 90,000 miles.
TOM: But in both cases, the price should be half of what you were quoted.
RAY: So I'd tell this guy thanks, but you want to think about it. For the next 60,000 or 70,000 miles.