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Vapor Lock

I drive a 2003 Mazda 6. In the summer of 2005 and 2007 I was driving my car at an altitude higher than my normal Kansas altitude and experienced vapor lock. (just outside Limon, CO and Cheyenne, WY) The guy who towed my car in 2005 recommended a little diesel (1 cup per tank)to remedy the problem. My husband suggests also using premium gasoline. I have the oil changed regularly and never use ethanol blends. I'm about to head out again this summer to Wyoming. Have you heard of vapor lock in a new car like this? And have you heard of this solution? THe premium gas and diesel did seem to resolve the problem.


  • edited July 2009
    Is your car fuel injected or does it have a carburetor. I don't believe vapor lock is a problem with fuel injected engines, but you learn something new every day.
  • edited July 2009
    Vapor lock was much more common in cars of the 40's and 50's and seems so rare today that I wonder if you really experienced vapor lock. Old cars with mechanical fuel pumps only develope about 4-5 lbs of pressure. The high heat in the engine compartment combined with high ambient temperatures could get so high that the liquid fuel would vaporize in the fuel line(s) leading to the carburator. The carburator is set to vaporize liquid fuel and couldn't handle fuel already vaporized and the car would stop. You'd open the hood and wait for the motor to cool or for a quicker fix carry water in the car to dump on the fuel lines to cool them and then fire up the car and be off.

    Fuel at higher pressures does not vaporize in the fuel lines and modern cars with fuel injection all use high pressure systems. To get vapor lock in your car you'd need a problem such as a weak fuel pump that is not producing the high pressures it is supposed to generate.

    Instead of vapor lock what is more common in today's cars is the electrical components overheat and heat kills electronic things pretty fast.

    I'm not saying you didn't experience vapor lock, but if you did it is very unusual in a car such as yours. I don't know about the cupful of diesel, and I don't think the differences in vaporizing of regular or premium fuel is much different. Perhaps a pressure test of your fuel pump would be advisable?
  • edited July 2009
    I've never heard of this, but my guess was that he was suggesting the diesel fuel as an additive to reduce the octane and effectively enhance the detonation characteristics of the fuel. Lower octane fuels detonate more readily. Interestingly, your husband's suggestion would have the opposite effect.

    I'll have to ponder this before agreeing or disagreeing with it. It's new to me.

    Vapor lock is highly unusual in a fuel injected vehicle. we've had long dissertations on the subject. Basically, the entire fuel system is under high pressure from the pump to the injector, so the opportunity for fluid boiling just is not there.

    I don't know why your vehicle stopped. It may have been because the system was unable to compensate for the sparse air. But I find the post interesting and anxiously await the inputs of others more knowledgable than I.
  • edited July 2009
    '03 Mazda 6's were multiport injected.
  • edited July 2009
    I doubt it was vapor lock, unless you have a defective fuel injector. The fuel is held at high pressure until injected into the engine, altitude should have no effect (otherwise you'd see lots of cars at the side of the road in high altitude areas). I also recommend against the diesel solution. Premium sure won't hurt, but I don't know why it would help. Both would increase the octane (make the fuel harder to burn). If was me, and assuming no codes were created in the computer (did no lights go on?), I might run the max dose of Techron fuel treatment through it (get it at Walmart, read the label) and run premium, just in case. But that's all just based on hoping it cures a problem I can't explain...
  • edited July 2009
    I seem to recall from other episodes you actually can use a lower octane gas in the mountains. Fill your car up with the minimum octane requirement would be my suggestion. Is premium suggested in your manual? That would tend to go with adding diesel as the net effect is a lowering of octane, I think.
  • edited July 2009
    Vapor lock can and does occur on fuel injected vehicles.

    A fuel injected system is a closed loop system. That means whatever fuel isn't used at the engine is returned back to the fuel tank. As this cycle continues, the fuel gets heated at the fuel rail(s) and starts heating up the fuel in the tank. This gets worse when the fuel level in the tank drops. This fuel in the tank becomes more volotile the hotter it gets, until it returns back to the hot fuel rail where it starts boiling and you have vapor lock. E10 gasoline also adds to the volotility of gasoline.

    So on those hot days on the road, keep your gas tank a half full or more, and try to avoid E10 gasoline.

  • edited July 2009
    My husband suggests also using premium gasoline.

    No, if anything you need lower octane in the mountains. Note: That does not mean you NEED lower octane, only that your car will get along fine with lower octane.
  • edited July 2009
    I'm not a fan of the vapor lock theory.
    Your car was towed so what were the circumstances and symptoms to cause it to be towed?

    Quit instantly on highway, stalled in traffic, sputtered and coughed before giving up the ghost, etc.?
  • edited July 2009
    I picked 5 "vapor lock" sites at random off the net,all said vapor lock on fuel injected cars "highly unlikely".
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