Dear Dave,
Is it legal to let your car idle for a period of time to warm up the engine? I was told there are some states and even cities that do not allow it due to safety and environmental concerns? —Seminar attendee
From Dave:
While conducting seminars at the Philadelphia RV show this past weekend, I had an attendee question whether it was legal or safe to let a vehicle idle for a period of time to help the engine “warm up.”
Having lived in the upper Midwest all my life, I am familiar with this. I recently found it is also called “puffing.” Idling periods are typically lengthy in my area during the winter, especially if the vehicle is parked outside for an extended period of time and the windshield needs to be defrosted.
Also, when a vehicle sits in below-freezing weather, the materials such as plastic, fiberglass, and glass are very cold, even frigid, and can be brittle.
One of the issues we experienced at Winnebago in the winter was starting a cold unit and driving it before everything warmed up. One good bump could create a large crack in any of those materials, so we did let the unit “puff” for a long time.
What I learned
I did a little research, and there are some regulations regarding extended idling. They vary by state and sometimes the situation.
Iowa Code 321.362 requires unattended vehicles to have the engine shut off and the emergency brake activated. According to the Department of Administrative Services (DAS), state employees operating DAS pool vehicles are limited to 5 minutes of idling to reduce emissions and fuel consumption.
During my research, I found a list posted by the popular RV app, AllStays. It lists regulations for idling in every state. You can find the list here.
What about remote start vehicles
Most of the regulations I found pertained to an unattended and unlocked vehicle. That not only is a safety risk, but is also an invitation for theft. Using a remote start feature requires the vehicle to be locked before starting the car. My truck has a remote start feature and will shut off after 5 minutes of running without the door being opened and the key inserted into the ignition.
Keep in mind, the longer you allow a motorized RV to idle, the more heat gets generated from the exhaust, especially the catalytic heater and exhaust chamber in a diesel. Without airflow from driving, the heat rises and can make for a soft floor. I have witnessed that dozens of times.
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My truck has remote start. I don’t use it often though unless the windshield is covered with ice.
As far as warming up the plastic parts, it does very little. Mine, and I believe most, kick on the defrosters. Very little heat from the air vents.
I cannot imagine it heating the interior parts of even a small RV.
For owners of Sprinter-based RVs, Mercedes specifically recommends against excessive idling. It’s well documented that it causes issues with the EGR and DPF systems, which can be very expensive to fix. Frequent short trips where the engine doesn’t fully warm up are also problematic.
More generally, manufacturers universally state that the best way to warm up a vehicle is to drive it.
Absolutely agree! Another reason for not practicing extended idling, “puffing”: the vehicle uses a lot more DEF fluid at idle than it does at normal operation.
Living in the south, we use remote start to cool down the interior before getting in.
For my two-year commitment of military service, after 16 weeks of combat basic training I was sent to Ladd AFB in Alaska, walking distance from Fairbanks. Throughout winter during the 1953 and 1954 winters the temperature was generally below zero. Sometimes close to -40 degrees. Those few men that had cars and lived off base mentioned having to leave their cars idling all night long and all day long (it was dark during daytime) or the car would not start. In the army motor pool, they sometimes would have to connect two or three trucks together to start one. That one would help start the others.