MPG and Propane in cold Canadian weather question. So I went over to my neighbour and asked him for an answer. To above Q., Being he’s both a Mechanical and Petroleum Eng. who owns a manufacturing co. specializing in building oilfield heating equipment using waste heat from the truck exhaust, hydraulics, and glycols, he should know what he’s talking about. (Side bar - his latest creation is a heating unit using 2 burners on it, each equal to 800 house furnaces, burning 7-800 gallons of diesel per hour, he’s got 4 to build) Anyway, as to propane, it’s a liquid under pressure, expanding to 270 times when the pressure is released, as I understood it, it boils off when you release the pressure, this happens at -44F. Temp affects the pressure; (I know I lost some of it here) just as water boils at high temps so propane expands at temp, if you take it from 150F to 600F it will expand 25%. So by going down in temp. likewise you loose pressure, but the move is the same. We have lots of vehicles and job sites using propane for heat here all winter, no problem till really cold. Then he got into the whole 2.15 percent to 9.60 percent propane vapour to air mixture to cause ignition and I just zoned.
As for the MPG question, his claim is that today with all the air/coolant sensors we don’t see the MPG drop of days gone by. If the thermostat isn’t opening/closing right and marinating heat in the block, the computer is reading that and it will over fuel, hence higher MPG. Fuel doesn’t vaporize as well in the cold, so the computer may run a richer mixture till the engine is warm. Also we idle vehicles here more for the car heaters. Back in the day when I worked rigs, we’d leave the pick ups run all night (not our gas) so they’d be warm in the AM when we left camp. He also got into the whole issue of how many BTU's are in that specific gallon of gas etc. and that it doesn't matter what you do to that particular gallon at that stated BTU, a BTU will only provide so much energy, etc. etc.
That my story, that’s all I saw, and I'm sticking to it.