Cooked relay is cause of incessant warning signal

Dear Car Talk:

Recently, we left the keys in the "on" position overnight in our 1995 Mitsubishi Montero. The next day, the battery was drawn down to the point that the car would not start. I hooked up my battery charger, which has two boost levels. At the low level, it still cranked poorly. I switched to a 150-amp boost and had my wife crank the engine. The car started right up. However, now the warning signal that sounds when you leave the headlights on or the keys in the ignition goes off as soon as you open the door, and continuously when you start and run the engine. It does stop when the door is closed and the key is not inserted. There appears to be no other problems. The instrument panel lights operate normally. The car drives normally, but that constant "peeeeeeeeeeeeeeee" can get a bit annoying. Do you have any idea of what happened and what should be done? My wife doesn't want to just throw money at this noise until we have an idea of what kind of job it might be. Thanks for your help. – Terry

RAY: I can tell you how to stop it, Terry. Take a 2-foot piece of 3/8-inch rubber tubing, and get your head under the dashboard while the buzzer is sounding. Using the tubing like a stethoscope, put one of end of the tubing in your ear, and move the other end around under the dashboard until you find the little relay that makes the noise. It's up under the dash somewhere.

When you find it, unplug it, pull it out and step on it. That’ll stop the noise.

I’m guessing that when you left the key in the “on” position all night, a door was ajar – or the switch on the door frame that tells the car the door is closed is failing – and that buzzer stayed on all night. And it cooked the relay: That relay got so hot that it welded itself in the “on” position.

I don’t know if that relay also serves any other functions. After you remove it, you may find out. If you notice that something else stops working – like your headlights – then you’ll need to replace the relay. So don’t stomp on it after you remove it; hang on to it so you can take it to your auto-parts store (or your favorite online parts supplier) and match it.

If the relay is exclusively for the warning buzzer in that car, then you can just take it out and leave it out if you want to. Just remember, it’s then incumbent upon you to notice if you’re driving around with the door open.

Premium gas not necessarily better for your car than regular

Dear Car Talk:

Can I use any grade of gasoline for my 2015 Lexus ES 350? A friend just told me I was wasting my money by filling the tank with mid-grade and an occasional tankful of premium. Won't using regular gas harm the car? – Dee

RAY: No. Regular is exactly what your car needs, Dee.

People mistakenly think of gasoline grades as “good, better and best.” That’s because gasoline companies have done a masterful job of marketing. By calling the higher-octane fuels “Premium,” they’ve convinced people that higher-octane is somehow better. It’s not.

Instead, think of octane like your shoe size. If you wear a size 9, would you buy a size 13 because it has a higher number and therefore has to be better? Of course not. You’d end up with blisters. And maybe some extra money from working as a birthday party clown.

The octane rating is a measure of the temperature at which the fuel will detonate inside the cylinder. Every engine is designed to be used with fuel of a specific octane.

You don’t want fuel with a lower octane than is required (because you can get pinging, or pre-ignition, which can damage the engine), but you don’t want fuel with a higher octane, either (because you’ll be throwing away your money).

And since Lexus says, in the owner’s manual, that your 2015 ES 350 is designed to run on 87-octane fuel, that’s what you should get.

In the old days, you used to hear that using higher-octane fuel had all kinds of beneficial properties: It would clean out your carburetor; it would remove carbon from your pistons; it contained special detergents to clean your fuel injectors; it would regrow hair.

All of those are false. Cars don’t have carburetors anymore. Carbon doesn’t build up on pistons. And fuels of all grades contain detergents.

So save your money, Dee. Buy the grade of fuel recommended by your manufacturer, and wear the right size shoes, too.

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