Q: Dear Tom and Ray:

I reverently brought my 1993 Mazda Miata to one of those quick-change lube places. When I got home I noticed that the little window sticker said 20W-50 instead of the usual 10W-30. Should I go back and have them drain this oil and refill it with the usual, or is the thicker stuff okay to keep in there for the next few thousand miles? I live in Los Angeles.

-- Dave

A: TOM: You're probably okay with 20W-50 in Los Angeles. If you lived in Anchorage, I'd tell you to march right back. On the other hand, if you lived in Anchorage, you probably wouldn't be driving a Miata!

RAY: The 20W-50 is a higher-viscosity oil. It's designed for hotter climates, severe duty--or sometimes as a last resort for junk boxes that are burning thinner oil at an unacceptable rate.

TOM: But in my experience, the only effect it will have is on your fuel economy. Since the oil is thicker, it takes a little more energy to move the engine parts around, and your mileage may drop by a fraction.

RAY: But mechanically it shouldn't cause you any problem. In the future, you might want to let them know at the outset that you want 10W-30 (actually, most newer cars call for 5W-30, so check your owner's manual). And let them unload the 60,000 gallons of 20W-50 they got on sale on somebody else.

Q: Dear Tom and Ray:

I need to run a two-wire, 12-volt cable from my battery to the amateur radio transceiver in the driver's compartments. The local Ford dealer could not recommend a location to put the cable through the fire wall. But it must be possible. Can you tell me how to place a small cable through the fire wall without doing any damage to the vehicle or the cable?

-- Dallas

A: TOM: There are three ways you can do this, Dallas. Actually four, if you count going to a place that installs car radios and saying, "Here, put this thing in for me."

RAY: But we know that since you're a ham radio operator, you want to be self-reliant and do this yourself. So the easiest approach is to find a wire under the dashboard that already carries 12 volts. You can easily tap off, for example, the cigarette lighter, which is already fully protected with a fuse.

TOM: The second easiest thing to do--if you want to run a new wire--is to use an existing hole in the firewall. There are already lots of wires coming from the engine bay into the passenger compartment. And you should be able to sneak an additional wire among them and not have to drill a new hole.

RAY: If there's no room for an additional pair of wires there--or if you're just dying to drill a hole (which is what we suspect), then you can just go ahead and drill away. As long as you're careful not to, say, drill into the heater core, you won't do any damage to the vehicle by making another small hole in the firewall. Just be sure to fit a grommet into the hole before feeding the wires, so the wires don't chafe and cause a fire.

TOM: And speaking of causing fires, if you do run your own wire, be sure to put a fuse for it as close to the battery as possible. You want to be sure that if anything does go wrong, the fuse blows before the passenger compartment goes up in flames. I know you ham radio guys love responding to fires and emergencies, but you probably prefer that they not be your own.

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