Vapor Lock

Vapor lock? What’s that? There you are, chugging up Trail Ridge Road, and your car starts to lose power. You pull off the road and the engine dies, and now the car won’t start! Arg! Don’t call a tow truck yet – it might not be serious.

Vapor lock occurs when the gasoline in your engine turns into vapor. This can happen due to high heat or high altitude, where gas turns to vapor at a lower temperature than normal. Often it’s a combination of both heat and altitude. Essentially, your engine is no longer getting gas. (Isn’t it funny that gas doesn’t work when it’s a gas?)

Symptoms include power loss, a feeling that the car is about to stall, a rough engine, or the car cranks but won’t start.

You can help prevent vapor lock by keeping your tank full, and by shifting into lower gear when driving up steep hills. Keeping the air conditioner off also helps.

If you start to notice power loss, don’t punch down on the gas or you’ll make it worse. Instead, shift into neutral and rev the engine.

If the car dies and you can’t get it started, try:

1) Loosening the gas cap, using a rag to help you. Be careful and stand back so as not to be sprayed by gasoline.

2) Starting the engine with the pedal all the way to the floor (don’t pump the pedal).

3) If that doesn’t work, open the hood and let the car cool for about half an hour and then try again.

If you can’t get it started after half an hour, there may be something else wrong. You may wish to call a tow truck at that point.

If you don’t have a cell phone or your cell phone doesn’t have service (which is common in Estes Park and Rocky Mountain National Park), then flag down a passing motorist and have them report your problem to the nearest ranger station. They will need to know your name, your location, what kind of car you are driving, what the license plate number is, and what the car’s symptoms are. If you have a motor service such as AAA, they will want to know that as well.

The more engine-savvy folks can try the following vapor lock remedies too:

Wrap a wet cloth around the fuel line. I’ve also heard of wrapping the fuel line with aluminum foil to attempt to prevent vapor lock in the first place.

Carefully hold open the choke flutter valve in the carburetor with a screwdriver. Just don’t ask us where the choke flutter valve is. (Hey, at least we know what a carburetor is!)

Fortunately, vapor lock is becoming less common thanks to today’s fuel injection systems, but it does still happen occasionally with older cars. Newer cars can sometimes get vapor lock too, especially when filled with gas that has a high ethanol content (the ethanol is more volatile). Just remember to take a cue from your car-stop for awhile, cool off, and enjoy the view.

2 thoughts on “Vapor Lock”

  1. I have a 2011 ford focus..every summer for the past 3 yrs it has starting problems or will die if at a stop..only happens in the summer..and only here and there..ive had 3 mechanics look at it all they do is shake there heads and charge me..

  2. If vapour lock occurs, it has the same symptoms as running out of fuel. On our diesel, we get this “glitch” on an intermittently, so now carry the correct spanner to bleed the system at the filter under the bonnet. We basically follow the priming procedure, but keep manually priming the pump on the top of the fuel filter and releasing the bleed valve until liquid fuel, rather than vapour comes out, before trying to start the engine.
    This is the text from the official Manual:
    CAUTION: Cranking the engine for an extended
    period with out a fuel supply may result in damage
    to the high pressure fuel pump. DO NOT force the
    plunger when priming the fuel system. Damage to
    the plunger or fuel filter/water separate will result.
    NOTE: Should the vehicle run out of fuel, the fuel
    system must be re-primed in order to start. Factors
    such as temperature, how long the vehicle
    has been sitting, and engine cranking speed will
    influence how quickly the engine starts. If the
    water in fuel light is illuminated in the instrument
    panel, refer to the water in fuel sensor for draining
    The fuel system must be primed if the fuel system has
    been serviced. This is done using the fuel primer button
    located at the top of the fuel filter/water separator.
    1. With service completed on the fuel system.
    2. Depress the fuel primer 20 consecutive times then open the bleeder screw on top of the housing to dispel
    trapped air.
    3. Close the bleeder screw and continue the step above until the primer button becomes slightly harder to depress.
    4. Turn the ignition to START and crank the engine a maximum of ten seconds.
    NOTE: If the engine does not start with in ten seconds, repeat the priming procedure. The engine will typically
    start within ten seconds; the engine may idle, idle rough, or stall, purging any trapped air from the lines and filter.


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