Vapor lock problem?

Hi, I have a 1995 Nissan Quest. My question is when I am idling in heat/(90+)/humid/weather my car cuts off. After about 15-20 minutes my car will start back up. Is this a vapor lock problem in the gas tank as the last time it happened I could hear the fuel pump. Is there a solution for this problem as I moved to Texas last year and will be living in HOT weather this summer. I love my van and don’t want to have to buy a new vehicle if this problem is fixable. Thanks!

Contrary to what most people believe, vapor lock can and does occur on fuel injected engines.

A fuel injection system is a closed loop system. This means whatever fuel isn’t used at the fuel injectors is returned back into the gas tank. This returned fuel has been subjected to the heat the fuel rails absorb from sitting above the engine. So the fuel begins to act as a coolant and returns this heated fuel back into the gas tank. If conditions are right, this returned fuel can begin to heat up the fuel in the gas tank. The more heated gasoline becomes, the more volotile it becomes. So eventually the fuel becomes volotile enough where underhood temperatures cause the fuel to boil. Or vapor lock. This is more of a problem if the fuel contains any ethanol.

If vapor lock is occuring, it usually means underhood temperatures are too high. And one of the first things to check is the cooling system. If the cooling system is no longer able to efficiantly remove heat from the engine, the underhood temperatures go up.


The effect Tester describes is especially true when exacerbated by an ethanol blend in the fuel, which most states have these days during at least part of the year. Ethanol turns to vapor at a lower temperature than regular gasoline and so is more suceptable to vapor locking. That said, the reason why a fuel injected car shouldn’t vapor lock is because the fuel should be under enough pressure that the pressure itself stops it from vaporizing in the lines, sort of like how your pressurized coolant system prevents the coolant from boiling. If your fuel pressure is low due to a clogged fuel filter or a weak fuel pump, this will also make your van much more suceptable to vapor locking. This might be the first indication of a fuel pump on its way out.

However, this isn’t the only possibility. There are also various electronic components on your car that if they’re borderline worn out will stop working in the heat. The ignition modules on some cars are notorious for this. An instructive experiment would be to get a spark tester from an autoparts store (roughly 5 bucks) and, next time it happens, check to see that you have spark during the non-starting episode.