Cold Mornings, Cold Engines

This morning we had a customer in with thermostat problems who started his explanation of symptoms with, “so after I let the car warm up for half an hour…”

Seem a little long to you? While it is always a good idea to warm your car up on a cold morning (below freezing), a minute or 2 is quite sufficient. What really warms your car up is the actual drive. Just like a person on the move will warm up much more quickly than one sitting down, a car on the road will heat up its engine faster than one idling in the driveway. In fact, letting your car idle for that long can even be detrimental to the engine (not to mention the environment).

Another related problem we have seen a lot of lately on these cold days is no-starts. For a number of these customers, the same little slip-up was to blame. They started their car then shut it back off in a matter of minutes. Maybe they just had to move it from one position to another, the driveway to the garage, let’s say. Then the next time they went to start the car, the engine would not start. The problem results from a flooded engine.

To start with, air drawn into an engine is mixed with atomized gasoline in an approximate ratio of 14.7(air):1(gas). This provides the best combination of economy and power. Depending on the conditions, either more fuel (richer mixture) or less fuel (lean mixture) is needed. When a cold engine is started, some of the atomized fuel contacts the cold surfaces in the intake runner and condenses back into liquid. Gasoline must be in vapor form to burn, so the computer provides additional fuel at cold startup to make up for the fuel lost to condensation. As the engine runs and warms, the computer makes adjustments accordingly. If the engine is switched off during the first few seconds of running, the condensed fuel can remain clinging to the intake surfaces. At the next cold start, the rich fuel mixture injected is added to the left over fuel and flooding results.

The best way to prevent this issue is to avoid a short start/stop scenario. If you need to move your car a short distance, consider driving it around the block before you re-park it. At the very least, let your car idle for a few minutes, possibly pressing the gas pedal (while in park) to bring the RPMs up. This will help keep you from suffering the annoyance of a flooded engine!

Written by Maria W.V

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