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Chrysler Propane Cars: Dodge Diplomat, Plymouth Gran Fury and Caravelle

In 1981, Chrysler started building propane-fueled Dodge Diplomats, Plymouth Gran Furys, and, in Canada, Plymouth Caravelles. Engineered and built by Chrysler, rather than the aftermarket, they kept their full factory warranty; and buyers could get parts from any dealer. They even had a police pursuit version with extra durability and performance parts, and, less surprisingly, a taxi option.

propane Dodge Diplomat

They quickly became the most popular propane-powered vehicles in Canada, with special suspensions to support the added weight of the propane tanks.

1986 Propane Dodge Diplomat Figures

Power: 150 hp @ 3,800 rpm
Torque: 260 lb-ft @ 1,800 rpm

Double-roller timing chain
Air-valve Impco CA225 carburetor
Impco EC1 lean mixture control
Impco VFF30 fuel filter/lockoff
US-spec HD5/Grade 1 fuel required

Chrome-alloy steel intake valves
Nickel-alloy steel exhaust valves
(Nimonic exhaust valves on police pursuit)
Viton valve stems seals/shields
High-temp caustic-cleaned coolant passages

The sole engine was the 318 V8, using special exhaust valve seats and valves, treated coolant passages, and valve rotators, which went through 4 million kilometers of durability testing. The main change during the program’s life was the adoption of fast-burn cylinder heads in 1986 (along with other 318s), increasing power to 150 hp and 260 lb-ft of torque.

Propane burns cleanly, helping engine life; and propane tended to be cheaper than gasoline, in any case. The power output was quite good, compared with the gasoline-powered 318; one reason was the high charge density, helping increase torque, created by eliminating intake air pre-heaters.

To get that power, the company had to create new spark control timing; cold-weather testing likely showed the need for a dual-pickup distributor with low-advance timing during starts. Cold weather was also attacked with an automatic fuel primer and throttle-operated override switch; while cold idle was helped by the thermostat-controlled two-speed idle system.

The Impco carburetor had the largest Impco vaporizer available (model E), and had a higher capacity than usual for the engine size to maintain power in cold weather. Vaporizers were internally coated with a propane wetting agent.

Chrysler used computers to select the safest fuel line locations, and to do extra structural analysis to avoid problems with metal fatigue, corrosion, and impact damage. The aluminum-clad tank was build using a flame-spraying processes pioneered by Chrysler Canada, so that the aluminum was mechanically and chemically bonded to the tank. Fuel lines had double-wall steel tubing covered in lead alloy and wire-armored where needed.

While aftermarket conversions usually placed the fuel tank in the trunk, Chrysler cut out the bottom of the trunk (by the spare tire), and added two propane tanks in that area, leaving some trunk space; the spare was moved elsewhere in the trunk. One casualty was the rear anti-sway bar.

The tank held 79 liters (17.4 imperial gallons), providing about the same range as gasoline cars.

Alternative fuels | Main technology page | Engines page | Chrysler and the environment, 1993 | Chrysler tech firsts

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