Radiator-cap diagnosis sounds suspicious

Dear Tom and Ray: My wife went to a quickie oil-change place, and they told her that her radiator cap needed to be replaced because it wasn’t holding pressure anymore. She called me and asked if she should let them replace it. I asked how much, and they quoted $15. I said no, and that I would take care of it. I went to the auto-parts store and replaced it for $4. The next time she needed an oil change, they told her the same thing, and she agreed to it and spent the $15. Needless to say, I was annoyed; her radiator cap was only three months old. Then I went to the same place with my car, and watched them change my oil. They took my radiator cap, and stuck what looked like the ball tap to a mini keg on it. They pumped the thing a few times, and told me that my radiator cap was not holding pressure and that I needed a new one. I said I would take care of it, but I am convinced that this pressure check was a scam. Was this a true test, or just a way to add $15 to a customer’s bill? — Patrick

RAY: It’s extremely unlikely that all three of those radiator caps were bad and needed to be replaced, Patrick. A leaky cap is not something we see very often in the garage, and to see it three times in the same family in a three-month period is pretty suspicious.

TOM: What happened was that these guys bought a new toy — a new piece of diagnostic equipment. So they’re using it on every car that comes in the door, in the hopes that their investment in the tool will pay off. And the test is real. But they either aren’t using the equipment correctly, or, as you suggest, they’re crooks.

RAY: The device they bought is a hand-pressure pump, designed to pressure-test a cooling system. It’s useful when you’re trying to diagnose an overheating engine and the cause isn’t obvious.

TOM: The hand pump is at one end of it, along with the pressure gauge, and you screw the other end onto the cooling-system recovery reservoir. Then you pump it up, and look for leaks. Or, if the leak is elusive, you leave it pressurized overnight and come back the next morning.

RAY: You can buy adapters for this pump that allow you to test the radiator caps, too. There’s a boatload of different adapters, because there are so many different radiator caps in use.

TOM: So one possibility is that they’re using the wrong adapters for your cars. Another possibility is that they’re just not getting your cap to fit on there correctly, so air leaks out when they test it.

RAY: And a third possibility is that when they bought this piece of equipment, they also bought 4,000 radiator caps that they now have to get rid of.

The right way to start a tractor

Dear Tom and Ray:

I am a college student who loves anything mechanical, and I work on a local farm to earn a little extra money. My boss likes to keep costs down, and that includes maintenance on tractors. That being said, none of the tractors have good batteries, and in the colder times of the year, you get only one shot of about five seconds to start them before the batteries die. My boss swears that putting the tractor in neutral with your foot OFF the clutch lessens the strain on the starter. I say it’s easier to start if you press down on the clutch while starting. Who’s right? I think he is wrong, but you can’t argue with the man who signs the checks. — Jeremy

RAY: No, you can’t argue with him. But you can ignore him. You’re right, Jeremy.

TOM: When you start the tractor with your foot off the clutch, you’re forcing the starter to turn not only the engine, but also the main shaft of the transmission. So right there, you’re giving the starter more work to do.

RAY: Add to that the fact that it’s cold out, and that 90-weight gear oil in the transmission is thicker than my brother’s skull.

TOM: That’s thick!

RAY: When you step on the clutch, none of that stuff in the transmission is turning; you’ve disengaged the transmission from the engine. And if you’ve got limited battery power, that’s absolutely what you want to do — for cars as well as tractors.

TOM: In fact, if you start cranking the engine with the clutch pedal out, and then push it in mid-crank, you’ll be able to hear the engine start to crank faster.

RAY: So you can do one of two things with this newfound knowledge, Jeremy. You can quietly use it to your advantage, and start the tractors the right way by pushing in the clutch.

TOM: Or you can go wave this article in your boss’ face, and then after he fires you, you can use this information at your next job.

Send your comments or questions for Tom and Ray to: Car Talk Plaza, P.O. Box 3500 Harvard Square, Cambridge, MA 02238. Listen to them Saturdays at 10 a.m. on 91.3 FM or 88.5 FM. Visit them on the Internet at www.cartalk.com.

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Ray & Tom Magliozzi