What happens when gas sits around inside a car that's been parked for a year?

Dear Car Talk

Dear Car Talk | Oct 01, 2006

Dear Tom and Ray:

My son has been in Iraq for almost a year. He left his car with us, and it has been sitting in the driveway the whole time. My plan is to sell the car and send the money to my son. I put in a new battery a couple of days ago and was able to start it. It would idle, but when I tried to drive it, there was a problem. I really had to rev the engine, and it seemed to be starved for gas. I had it towed to the local mechanic, and he said the fuel lines and carburetor had a buildup, and that it would cost about $500 to clean out. Any chance a gas additive in the tank and/or some spray cleaner will clean it out? -- Gary

RAY: Before you do anything dramatic -- like spend $500 -- start by trying some simpler things, Gary.

TOM: First, you probably have old gas in there. Gasoline breaks down over time, not only becoming less effective as a fuel, but also releasing gums and varnishes into the fuel system. Carburetors in particular are vulnerable to having their small passageways gummed up by these varnishes. And the longer the gasoline sits, the more varnish is created.

RAY: So, I'd start by getting that old gasoline out of there. Siphon out whatever you can, and fill the tank with fresh gas. Or, if there's less than a quarter of a tank in there, you can just fill the rest of the tank with new stuff and dilute the old stuff.

TOM: And at the same time, dump in a couple of cans of good fuel-line cleaner. We've had particularly good luck with something called 44K from B&G Industries. But that can be hard to find. So you can also use Chevron Techron, or Gunk Fuel System Cleaner.

RAY: Then take the thing out on the highway. I wouldn't be surprised if after 25 miles, the thing is fixed. The new gas will combust better, and the fuel-system cleaner might clean out enough gums and varnishes to make the carburetor happy.

TOM: If those steps don't work, then you will have to get the carburetor rebuilt. That involves taking it apart, cleaning it and replacing some key parts, like the jets, gaskets, needle and seat. That'll definitely fix it. But then you're into hundreds of dollars.

RAY: And by the way, Gary, if your kid is unlucky enough to get sent back for another tour of duty, try this: Put some gasoline stabilizer, like Sta-Bil, in the tank before parking the car for a year. That'll keep the gasoline from going bad. Or better yet, have him sell the car before he goes. Not only will it be in salable, good running condition, but he'll get a better price for it, because the average car's value declines over time. Our best wishes to you both.

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