What's the cure for vapor-lock-- when it's 145 degrees outside? Find out.

Dear Car Talk

Dear Car Talk | Jan 01, 2007

Dear Tom and Ray:

I'm a soldier in Iraq, and I have a problem with what I suspect is vapor lock on a 2005 Polaris Rover all-terrain vehicle. Frequently (although usually occurring during the hot parts of the day and after driving about 2-4 miles), the Rover stalls out. If we let it sit and cool off (although that's wishful thinking around here) for about 20 minutes, it starts and runs fine until it gets hot again. I know new cars don't have vapor-lock issues anymore (as a rule), but this is not a typical vehicle with PCV and other improvements, and I'm fairly sure that's the problem. Before you laugh me off, I should mention that here in Southern Iraq (Camp Bucca), the average daily midafternoon temperature is 120-145 degrees Fahrenheit! We've cleaned the carburetor and the air filter. There is no fuel filter. We also checked the cooling system and electrical system. My mechanics can't seem to find anything specific for a cause. And most of them are so young, they've never heard of vapor lock. I remember the late '60s and early '70s, when this was a big summer rush-hour problem. However, I don't remember a specific remedy for this problem. Can you help prove me wrong or help rectify this problem? My soldiers and I would appreciate that, because if you think 145 degrees sounds hot, try walking 2-4 miles in it in full body armor! Thanks! -- Major Rick

TOM: I think we can help, Rick. Since it's 145 degrees out, I agree that it's vapor lock.

RAY: I assume you've tried wrapping the fuel lines to try to insulate them. If not, do that first. But the real solution is to add a booster fuel pump near the tank.

TOM: Modern cars prevent vapor lock because their fuel pumps are inside the gas tank. That keeps the fuel under constant pressure from the tank all the way to the fuel injectors, and never gives it a chance to vaporize. But in the Polaris, you probably have a mechanical fuel pump, which is pulling the fuel to the carburetor rather than pushing it.

RAY: So you need to push it. To do that, you install an electric pump as close to the fuel tank as possible.
Sure, it'll have to pull the fuel a short distance out of the tank, but then it'll pressurize the fuel line and send it the rest of the way under positive pressure, leaving no room for vapor.

TOM: I don't know how strong a pump you'll need, but just a few PSI might be enough to fix the problem.

RAY: If that doesn't work, you'll have to load up the ATV with bags of ice. Then, when it vapor-locks, you can either lay the ice bags over the fuel line to cool it down, or put them on your head for the walk back! Good luck, Rick, and I hope you and your fellow soldiers return home safely, and soon.

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