When I bought my tow vehicle, I talked to other full-time RVers about whether I should go diesel or gasoline. The general consensus was that diesel would get you more power going up an incline, but in flat areas, gas would be fine. However, no one ever discussed the concept of “altitude” with me — and I learned the difference between the two the hard way as I just drove through the Rockies for the first time this past week.
Let me start by thanking my friend Paul the mechanic for explaining to me (patiently, several times, and with visual aids) how engines convert liquid fuel into kinetic energy through internal combustion — not my strong suit! As each piston in a gasoline engine moves up and down in turn, it sucks air in through the intake valve and compresses it to create a vacuum in the engine. The air is mixed with gasoline, and the spark plug ignites the mixture. This series of small explosions keeps the engine’s pistons pumping inside the cylinders — which causes the crankshaft to rotate, which then turns the wheels so your vehicle moves forward (I apologize if that’s a really oversimplified version of “Engines 101” — but enough for you to get the point.)
A diesel engine works in much the same way as a gasoline-powered vehicle when idling (sucking in air and creating a vacuum in the engine) — but once you hit the gas, the “turbo” system takes over. As you rev the engine, exhaust gasses are routed into a special turbine before being shot out the tailpipe. The engine speeds up, the turbine spins faster, and the system shifts from “vacuum” to “pressure” — forcing more air into the engine. This forced air heats up as it is compressed and causes the fuel to ignite sans spark plug. That’s where diesel gets its superior power. Less-refined fuel (having a higher energy density) collides with an air compression ratio 2-3 times that of gasoline — you get a greater reaction and more “vroom.”
A gasoline engine is an “open” system — it requires an in-flow of air to help the gas burn. Diesel is a “closed” system — the turbo creates its own air pressure (its own “atmosphere,” as Paul says) and isn’t reliant on the quality of the air outside the vehicle. Why does this matter? It doesn’t, if you’re at sea level — but when you’re in a higher altitude, the air is thinner and contains less oxygen. Gasoline burns less efficiently and your vehicle isn’t going to perform as well. Count on a drastic reduction in both torque (how quickly you can accelerate) and horsepower (how fast you can go in a given gear) — especially when you’re pulling 6,000 pounds behind you. A diesel engine, on the other hand, can keep on cranking without a slow-down — even high up.
I read tons of articles on diesel vs. gas before I bought my truck, and the concept of altitude affecting your ability to tow was never once mentioned. I grew up in coastal community and did most of my driving in the southeastern U.S. — how the hell was I supposed to know? On my way through Vail Pass, I found my speedometer needle creeping ever downward — even with the truck in first gear and the pedal to the floor. WTF? Granted, it was a 7% grade — but I had just driven an 8% grade in Utah with no problem. I had successfully toted my Airstream up mountains in Tennessee, Georgia, West Virginia, Montana, South Dakota, California, Idaho — but these are all steep inclines at a much lower altitude. It wasn’t until I was bitching about my lack of horsepower to Paul once I landed in Denver, that I discovered there wasn’t actually anything wrong with my truck — problem was simply the kind of gas it used.
Of course, you can compensate for some of these issues, even when driving a gas truck. If you’ve got a good fuel injection system, it should automatically adjust to create the correct mixture of gas and air at any altitude. And here’s a neat little trick Paul taught me — if you’ve been driving at sea level, then head up into the mountains and find yourself slowing way down while trying to crest a hill, mash the pedal to the floor a couple of times and it helps your engine re-calibrate the parameters for fuel efficiency for higher altitude. Who knew?!
When I was shopping for trucks, I did a lot of back-and-forthing about which system would make the most sense economically, over the lifetime of the vehicle. Diesel fuel costs more per gallon than gas, but you get better mileage — at least twice as good as a gas truck while towing your rig. I also examined the up-front cash investment — a diesel truck could cost half again as much as we would spend on a gas truck. And I compared the cost of repairs (almost always more expensive) with the longer diesel engine life (you might get 500,000 miles out of a diesel, and barely half as much from a gas truck). You have to replace a gas truck more often when you work it hard the way full-timers do — but the lifetime savings on maintenance (when your labor and replacement parts cost less than half of what it would to fix a diesel) seem to balance out with the expense of the new truck. Dammit — that didn’t help me make a decision!
I needed to consider how often having a diesel engine would actually improve our truck’s performance. Very rarely do I drive in super-high altitudes — the majority of my travels are along the coasts and through the heartland, where even a gas truck can handle the big hills. I also spend most of my time driving without the trailer attached, which could be a problem. Diesels emit a lot of soot — if you’re towing something heavy and working your engine at full capacity, the system “self-cleans” by blowing a nasty cloud of schmutz out the exhaust pipe. But in-town driving doesn’t provide enough “oomph” — and the soot builds up until you have a nice layer of grimy cement, clogging your moving parts and ensuring an expensive repair bill.
Paul said that “under-utilization” of a diesel’s capabilities is the cause of most costly repairs on trucks and SUVs these days — it’s the “soccer mom” syndrome, when you have a vehicle with way more power than you need, you never pull anything with it, and only use it for grocery shopping and toting kids to and from extracurricular activities. I only tow for a few days at a time, every 2-3 months — so diesel could actually have been more trouble than it was worth (thank goodness, considering I already own a gas truck!)
So all-in-all, gas is a good choice for me — however, your situation may be completely different, and you need to evaluate all of these factors for yourself before committing to a particular vehicle. I’ll end by saying that I am far from an expert on this matter, but these are the bits of info I’ve picked up along the way as I RV across the country. Hope you find this useful and helpful — and at the very least, you know to ask about altitude when truck shopping (which I surely didn’t!)Click here for reuse options!
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