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Rig-Buying Consideration #11 — Gas Vs. Diesel

RV Blog -- GasWhen 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.) Wink

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!)

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    8 Responses

    1. Jim says:

      Try crossing the Rockies in an old, overweight, gas RV, towing a Jeep, and a clogged fuel filter on the RV just for EXTRA fun (did not know it was cloggged). It seems too, from your recent FB pics you have converted to diesel. For my next rig I want diesel. It is too hard to get this rig through the car gas pumps. Especially while towing the Jeep. You can NOT back up while flat towing.

    2. Ramona says:

      Actually, no — we just upgraded from an F150 gas to an F250 gas — even with the desire for more power, we still decided that diesel wasn’t for us :)

    3. Jim from dreamstreamr dot wordpress dot com says:

      We agree with you on gas vs diesel — We don’t area about the added torque, our 25′ trailer follows just fine behind our 3/4 ton with gas engine.

      Curious though — just realized you are offering your pictures for sale — are you selling many?


    4. Ramona says:

      I’ve only just started posting them and haven’t gotten all of my travel blogs up yet (and the site isn’t 100% live) — so the answer on the photos is not yet, but I expect to down the road :)

    5. Conrad says:

      You need to drive a diesel and you will never go back. You did not mention that they burn almost no fuel at idle. The fuel is not explosive like gasoline, so you can carry a large tank safely, for greatly extended range–important when towing and traveling on Sundays. Modern diesel run just fine with light loads. They can take other fuels in a pinch–dump in your used motor oil, or home heating oil in an emergency. If you drove one for a year, you would never want anything else.

    6. Ramona says:

      Good to know! I will see if we can find a friend to loan us one to try out. Who knows, I may end up a convert!

    7. Nate says:

      Hi Ramona, my wife and I just stumbled upon your site, very nice!

      Anyway, I hope you don’t mind me leaving my two cents on this topic here: We have a diesel and went with it for all the “pros” you listed above, however, we are now wanting to switch back to a gas vehicle. Why? Mainly because of ease/cost of maintenance (we are living mobile, and having to haul around heavy duty (and heavy!) or special tools to work on the extra heavy diesel motor (I do almost all the work myself) is a burden we’d like to be without) and the cost of fuel. While both fuels are expensive, when gas sometimes goes down and fluctuates a lot, diesel is quite stable at it’s higher price (around 80 cents per gallon difference right now!).

      Can I also clarify a few things about the two motors? The operation of positive air pressure in the intake of a diesel refers only to a Turbocharged Diesel, whereas a non-turbo diesel will still stuffer the same as a gas at high altitude (not all diesels are turbo, but most are!). On the other hand, if you have a Turbocharged Gas motor, you will benefit at higher altitudes just like a turbo diesel.

      If you find yourself still wanting more while driving high passes, you may want to look at something like the Ford EcoBoost gas motors.

    8. Jerry says:

      We pull our 25′ Airstream with a VW Touareg TDI. We also use the Touareg as our only car. It has a turbo charged 3.0 litre clean diesel and an 8 speed automatic transmission and pulls great. We got 18.9 mpg on our last camping trip.

      We’ll find out how it does in the Rockies next summer. Reports from others say it does just fine.

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