Q. I decided to change the auto transmission fluid in my wife's 2003 Ford Explorer.
My first problem was that I couldn't access the torque converter to drain it, so I dropped the pan, changed the filter, blew out the cooler lines, and put it all back together.
Then I discovered that there is nowhere to add transmission fluid, or even a dipstick to check fluid level. The owner's manual states that the transmission will not ever use fluid and doesn't need to be checked, as if an output-shaft seal or a pan gasket will never leak.
A. For openers, automatic transmission torque converters rarely have drain fittings anymore, so you can change only about half of the fluid at a time.
Look for a fitting with an Allen bolt in it in the bottom of the pan - that's the fluid-level adjustment/fill port. There's a special Ford tool that screws into the port.
You're supposed to fill the transmission by forcing automatic transmission fluid into the tool from another tool. It's basically simply a pressurized container with some fluid inside, an output hose and an input hose. Use compressed air to force fluid into the transmission. How do you know when it's full? Fluid will dribble back out of the hose.
If this sounds like a cockamamie way to do things, that's exactly what it seems like to me. Even if they recommend never changing the fluid, as some manufacturers do, how much could it cost to put in a dipstick and a fill port?
You could probably drip fluid into the transmission from above, using gravity, if you don't have a lift to get the foot-tall container under the car. Or if you don't have a compressor.
Q. I recently bought a Saturn Outlook, and I want to buy a locking gas cap for it. Nobody seems to have one for sale, and a dealership mechanic suggested that using one would possibly set off the engine-warning light. He said that it was better not to use one - yet the Saturn brochure lists it as a factory accessory.
So, is a locking gas cap something that you would or would not recommend?
A.The gas cap is an integral part of the vehicle's evaporative-emissions system. If it doesn't seal properly, the "check engine" light comes on.
This is a common problem on many cars, even with ordinary gas caps that aren't screwed down tight. Apparently the mechanic has seen some problems with the locking cap that Saturn sells.
Even if the light comes on, however, if the cap seals properly, it will go back off within a few hours. Try it. If the light comes on and stays on, change back to the previous, nonlocking cap.
Q. I have a 2005 Volvo XC70. When it was approaching 20,000 miles, I thought I should have the tires rotated.
My husband told me that his BMW dealership warned him that a car with all-wheel drive should not have its tires rotated or it will lose AWD function. However, I couldn't find anything online that says that a car with AWD should not have tire rotation.
A. I have no idea what "lose AWD function" means. Every industry source I know and rely on says that AWD cars need regular tire rotation, like any other vehicle.
Except for BMW, that is: That company's take is that the extra tire life isn't worth the expense of multiple rotations or the minor change in handling that you'll feel for a hundred miles or so after the rotation until the tires wear in slightly in their new location. BMW makes no distinction between RWD and AWD vehicles.
Actually, 20,000 miles is late for a tire rotation. I'd aim for every 10,000, and I'd have some local shop do it, rather than the Volvo dealer. Don't forget to insist that whoever rotates the wheels use a torque wrench to properly tighten the lugs, instead of simply rattling them tight with an air wrench.
Mike Allen is a senior editor for Popular Mechanics magazine. Questions should be sent via e-mail to driveit@nytimes.com.
