Paul Brand: Check for vapor leak as source of gasoline odor

Q I own a 1998 Dodge Caravan with the 3.0-liter V6 engine. I bought the car new, and at 43,000 miles the car developed a problem during cold weather: a strong gasoline smell inside the car.

After several attempts to fix this, the problem remains. Now that my son just got his driver's license and both he and my daughter drive this car, I'm concerned about their safety.

The problem is intermittent, but it happens only when outside temperatures are below about 20 degrees. When the car is idling at a stoplight with the heater going, you can smell a strong gasoline odor inside the car. When you start driving again, the smell gradually goes away.

Sometimes after driving the car in the winter, when I park it in my garage, shut off the engine and then go back in the garage a few minutes later, there is a strong gasoline smell.

The dealer could not identify the cause, so I took the car to an independent garage when the strong odor was clearly present, but it couldn't determine the cause. A couple of weeks later, the same garage replaced fuel injectors 2 and 5 after saying those injectors showed signs of leaking. The next winter, at 71,000 miles, the Dodge dealer replaced injector 1, saying it was leaking.

But the problem continues intermittently each winter. The car now has 119,000 miles on it, and I want to keep driving it a few more years. What's causing this? Is it safe to drive the car if technicians can't fix this?

A Has the dealer or independent shop checked the "evap" system? This is the evaporative fuel emission system, and it has a sophisticated monitoring system to determine whether any fuel vapor is leaking into the atmosphere from the fuel tank and associated components. The evap system is also monitored by the powertrain control module (PCM) and can be scanned for trouble codes. If that has not been done, start there.

By the characteristics of the problem -- only in cold weather and noticeable only while the vehicle is stationary -- I don't think the issue is an external fuel leak from an injector or other fuel system component. If there was such a leak, I think there would be clear visual evidence of it.

I'd focus on two components in the evap system -- the canister purge solenoid in the engine compartment and the charcoal canister mounted along the frame or chassis under the driver's seat. This system traps and stores fuel vapor from the tank until the PCM tells the purge solenoid to open, allowing engine vacuum to draw the vapor into the induction system and burn it.

Any vapor leak from any of the vapor lines to or from the fuel tank and those two components could generate an odor of raw gasoline. Because the purge solenoid opens only during certain times after the cold-start warmup period, any vapor leak between the solenoid and intake manifold would be noticeable only during those moments.

Q I have a follow-up question about your Nov. 22 column on how tire pressure drops in cold weather. Since tire pressure should be checked when the tires are cold and then properly inflated, what allowance should I make for the temperature increase after I have driven the five miles to the tire shop? Should I wait 10 or 15 minutes or longer? Also, I am thinking about putting nitrogen in my tires. Is that a good thing, or just hype?

A To rephrase your first question: How much will tire pressure rise in the five-mile drive to the tire shop? In winter conditions, I'd estimate not more than 2 or 3 pounds per square inch (psi). For example, if you want the tires to have 35 psi cold, set them at perhaps 37 psi after driving the vehicle to the shop. Then, recheck them cold the next morning.

Using nitrogen to inflate tires definitely isn't hype. One of my responsibilities for the race team I worked for in the '70s was to locate the welding supply house nearest each race track we raced at. That way, if we needed to refill a nitrogen bottle during a race weekend, I'd know where to go.

The race team used nitrogen in the race-car tires for the same reasons we should. Nitrogen is "dry," meaning there's no moisture in the gas to freeze or corrode, nitrogen pressure is more stable and doesn't change as much with temperature changes, and it's a bit less prone to minor leaks because of tire or wheel porosity -- all good things.

Motoring note With the cold and snowy start to the holiday season, here's a quick reminder to drive safely.

• Buckle up: everyone in the vehicle, every time.

• Horizon eyes: look as far ahead as possible.

• Slow down, brake early and brake lightly to help maintain traction in slippery conditions.

Happy holidays!