DEAR CAR TALK: Will a car be damaged if a person mistakenly puts diesel into a gasoline car's gas tank? And also, what happens if you put regular gas into a diesel vehicle? How often does this happen? It happened to us recently. Thank you.
-- Carolina
DEAR CAROLINA: Well, it's not something we see every day. First of all, diesel pumps are labeled "Diesel," and they're usually a different color -- most often green. So most people notice that something's different before they make that mistake.
I'm not making you feel better yet, am I, Carolina?
Actually, despite the markings, it happens surprisingly often, so don't feel too bad. I guess people are just busy and distracted these days, trying to refuel the car while responding to text messages and stopping the Cheerios fight the kids are having in the back seat.
When diesel fuel does end up in a gasoline tank, the car will run for a few miles or so, until all the gasoline that's still in the fuel line gets used up. At that point, the engine will shut down -- boom. Gasoline engines cannot combust diesel fuel, so the car would stop running.
Once that happens, it has to be towed to a shop, and the fuel system needs to be drained. We start by emptying the gas tank. Then -- assuming the car has been driven since the errant refueling -- we get all of the diesel fuel out of the fuel lines, the fuel rail and the injectors.
We'll usually remove the injectors and run them outside of the car so they just squirt out a bunch of the diesel fuel. Sometimes that doesn't work, and we have to take things apart, and, well, it can be a real mess. But it's doable. And normally, no permanent damage is done to the injectors, the seals or anything else. And because the car won't actually run on diesel fuel, there's little risk of damaging the catalytic converter.
But it's a costly and time-consuming process, as I'm sure you now know, Carolina! Depending on the car, it can cost from $500 to $1,000.
Accidentally putting gasoline in your diesel tank can be even more harmful, depending on how much gasoline you've added. I mean, if you had an empty 20-gallon tank, and you caught your mistake when you'd put in only a gallon, you might be all right if you filled the rest of the tank with diesel. But if it's more than that, you could create serious problems.
Aside from being the fuel, diesel also is a lubricant. So running a diesel engine on gasoline starves the fuel-injector pump of lubrication.
And because of their different combustion properties, the gasoline detonates too early in a high-compression diesel engine and causes all kinds of damaging knocking and misfiring. So not only would you have to drain the tank, in that case, but you might need to replace other parts as well.
So I think we need to launch a new public-service campaign to reduce distractions while refueling, Carolina: "Don't Text and Pump." Want to be the poster girl?
DEAR CAR TALK: My 2007 Toyota Sienna has a tire pressure monitoring system. It recently alerted me to a leaking tire, and I found the nail in the tire and took it to be fixed. The mechanic removed the tire, because he claimed it was better to seal the leak from the inside instead of just plugging the tire from the outside. While doing this, he noticed that the tire pressure sensor casing was cracked, and he wanted to replace the entire sensor. I told him not to do it, simply because I knew the sensor was working fine since it was the sensor that had alerted me to the leaking tire recently. Two days after the repair, the tire pressure monitor light is blinking, indicating a malfunction in the system. This is too much of a coincidence, to me. Are the sensors that delicate, or are the mechanics that clumsy?
-- Phil
DEAR PHIL: Well, first of all, your mechanic was right about sealing the tire from the inside. That's absolutely the right way to patch a tire.
Was he clumsy? It's possible. If he was really careless, and put the tire on the tire machine incorrectly, that could have broken the pressure sensor. But it's not very likely.
Was he dishonest? Did he whack the sensor by accident, and then shrug and tell you that you had a pre-existing crack? Again, it's possible. But at this point, how are you ever going to prove it? And it's just as likely that he was telling you the truth.
I think your mistake, Phil, was not agreeing to replace the sensor once you knew there was a crack in it. Now, instead of being out $75 for the sensor, you're out that much plus the cost of removing, remounting and rebalancing that same tire.
My brother used to say, "It's the stingy man who spends the most," Phil. I think he was absolutely right about that. Of course, he also used to say, "This is definitely my last marriage."
But here's a bigger issue to consider: If you trust this mechanic so little that you told him to leave a broken part inside your tire for fear of being ripped off, it's time to find a mechanic you really do trust. Get a recommendation from friends or family. Or check out mechanicsfiles.com for recommendations from our readers and listeners.
File this one under "lessons learned." And congratulations on your new pressure sensor and unnecessarily remounted and balanced tire, Phil.
Ray Magliozzi dispenses advice about cars in Car Talk every Saturday. Email him by visiting
cartalk.com
HomeStyle on 01/23/2016