Q: I'm thinking of buying a propane-fuelled used car. Are there any concerns I should be aware of?
A: Electrical engineer Eli Melnick of Start Auto Electric (startauto.com) replies:
Propane has been touted as a superior motor fuel for many years and conversions became popular in the 1980s as gasoline prices rose. It's said that while gasoline needs to be vaporized, propane is delivered to the intake manifold as a gas, thereby permitting more efficient combustion.
Although this is true in principal, earlier conversions just dumped propane into the intake without the benefit of fine metering or computerized controls. This is evidenced by the high number of propane vehicles that fail emissions testing. Recent technological advances and the use of sophisticated conversion kits have alleviated these problems. A modern propane installation can be integrated with the vehicle's fuel-injection computer, allowing for clean, fuel-efficient operation as well as seamless fuel changeovers (if the vehicle is dual gasoline/propane).
Eric Lai adds:
Consider only used cars with a fuel-injected propane conversion, generally 2005 or newer. Outdated "fumigation" conversions using a rudimentary add-on carburetor — similar to that found on a lawn mower — can spell trouble for unknowing buyers.
Last year, the average Drive Clean failure rate was below 10 per cent for gasoline vehicles but a whopping 34 per cent for propane vehicles, with 2002 being the latest model-year requiring biannual testing. In total, 2.5 million gasoline vehicles and just over 2,000 propane autos were tested.
Drive Clean blames "inadequate (carb) conversion systems" for elevated propane failure rates across all model-years up to and including 2004, whereas newer fuel-injected models (tested for resale) were fine.
A 2008 report by the Ontario Propane Association confirms that "propane-conversion technology providers did not keep up with the evolution of gasoline engine technology and continued to install carburetor-based technology that resulted in operational problems (backfires, reliability) and poor environmental performance that rendered the carbureted propane technology unviable."
Only in recent years have fuel-injected propane conversions, which resolve all these shortcomings, become the standard. The OPA report notes, however, that obsolete carb conversions are still available and being used by some low-cost operators (taxis, for example), though their use is "discouraged due to operational and emissions issues."
Police in London, Ont., have used propane cruisers for a quarter-century now. They've never had a fuel-related safety incident.
According to a published study, the 1983–2000 Crown Vic cruisers ran adequately, but starting with the 2001 model-year, compatibility of the propane carb system with newer engine computers became an issue and problems developed with backfiring and passing Drive Clean due to high nitrogen oxide emissions. Problems weren't fully resolved until mid-2004, with the adoption of a new fuel-injected conversion system.
Propane contains less energy than gasoline, resulting in a shorter driving range. The tank is heavy and consumes a lot of trunk space. Also note that most underground parking facilities prohibit compressed-gas vehicles.
However, using propane can cut fuel costs by about one-third and reduce greenhouse gas emissions by one-quarter over gasoline or diesel. Buyers of new or used propane vehicles receive a retail tax rebate of up to $750. Gasoline vehicles converted within 180 days after purchase also qualify.
The cost of conversion is about $4,000 and the system can be reused on cars you buy in future. When sold, dual propane/gasoline vehicles typically receive a $1,500 premium over comparable gasoline models.
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