CAR TALK: There’s only one way to tow an all-wheel drive vehicle

DEAR CAR TALK: I have two automatic transmission questions that have plagued me for over 50 years.

1. Is it OK to coast in neutral with an automatic transmission? I am asking from a potential damage problem, not the safety aspect.

2. Is it OK to tow an automatic transmission car on its drive wheels?

My father always taught me that it would ruin the transmission to do either, but I see cars being towed all the time on their drive wheels. Please help clear this up for me!

-- David

DEAR DAVID: Your dad was one for two.

Coasting with the engine running and the car in neutral won't do any damage to an automatic transmission. The reason it's discouraged is because if you're coasting down a long or steep grade, you lose the car's natural engine braking.

That can allow your speed to get out of control or force you to overuse, and therefore overheat, your brakes. Overheated brakes can fail, which is always bad news, but especially unwelcome when you're heading down a long hill at high speed.

On the towing issue, your dad was correct that a car with an automatic transmission should not be towed with its driven wheels on the ground, even in neutral. The reason you can't do it is because the driven wheels on the ground will turn the drive shaft, which will turn the internal parts of the transmission.

And an automatic transmission only gets lubricated and cooled when the engine is running. So if you tow it like that for any real distance at all, you'd likely ruin the transmission.

Fortunately, the majority of tow trucks now are flat beds, which lift the car completely off the ground for towing. That's in part because so many cars and crossovers are now all-wheel drive. And if all the car's wheels are driven wheels, there's no other way to tow it. It's also just safer than having a car bouncing along behind a truck. So flat bedding is what we'd always recommend if you're getting towed. That's always a safe option.

DEAR CAR TALK: What should I do? I put water in the radiator of my 2000 Ford Ranger, then headed to the next town over (about 13 miles). I was flying along at about 60 mph, listening to Pink Floyd, and I suddenly lost power.

I immediately pulled over and shut off my truck. White smoke came out from under the hood. At that very moment, I knew I had forgotten to put the dang radiator cap back on.

I called for help, which arrived about 20-30 minutes later. I lifted the hood and my truck was already cooled down. The tow truck guy and I added water -- lots of water -- not realizing it was running right back out underneath the car.

Luckily, the radiator cap was still sitting there on the motor where I had left it, but it doesn't look good, does it? I tried to start my truck but couldn't.

Can you help me?

-- Terrie

DEAR TERRIE: With what? A new car loan?

I think your primary problem was not that you left off the radiator cap. Your primary problem was the reason you were adding water in the first place. You had a coolant leak.

Whatever was causing it -- a bad water pump, a loose hose clamp, a cracked hose, a cracked cylinder head, a blown freeze plug -- during that 13-mile drive, or perhaps even shortly before that -- the leak went from moderate to catastrophic.

While you were driving along, rocking out to "Dark Side of the Moon," I'm guessing every drop of your coolant leaked out and your engine was suddenly on the hot side of the moon.

At this point, my guess is that you overheated and possibly melted the engine. When an engine gets badly overheated, you can actually melt the valves. Without working valves, you have no compression. And without compression, the engine is, as my bread-maker friends like to say -- toast.

So, before you even worry about how to fix the leak, I'd ask a mechanic to do a compression test and figure out why the engine won't start. If you've led a good, clean life, and it turns out to be something fixable, then you'll -- obviously -- want to take care of the coolant leak, too, before you get back on the road.

But it wouldn't be a bad idea to keep turning the pages until you find the car ads, Terrie. Hey, you can get an upgraded stereo, too.

Ray Magliozzi dispenses advice about cars in Car Talk every Saturday. Email him by visiting