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Old 05-18-2020, 04:57 AM   #1
Join Date: Sep 2013
Location: Virginia
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Gas Power versus Diesel Power (Food For Thought)


This post was created in the course of another discussion, and I felt it might be a good idea to make it its own thread, perhaps the admin will see fit to make it a sticky if they feel it serves a purpose. I don't claim to know everything, just giving my take on the subject. Perhaps other folks can offer their own insights as they see fit.

I have seen a few folks who are new to the skoolie community wonder why gas power isn't a thing these days, or mistakenly believing that gas power is not realistic or desirable in a skoolie. It really depends on the bus in question, which is dependent upon the era it was built.

Until recent years, most school buses as we know them were simply bus bodies fitted to incomplete medium-duty truck chassis. And many still are, I think mostly due to budget constraints. The modern flat-nose / rear-engine pushers are likely more expensive.

It also sort of came with the territory that for a long time, there just weren't many feasible diesel options for these buses. For a long time, diesel options were too few and too costly. Prior to the late 80s / early 90s, gas engines were just overall cheaper to buy, maintain and operate. Crowns were about the only buses even offering diesel options, and I suspect that was only because the Detroit 2-stroke was pretty standard in these. Even the flat-nose Blue Birds of that time exclusively used Ford's Super Duty gas V-8 (514 CID if memory serves), only offering a diesel option with the Caterpillar 3208's arrival on the market.

Until then, the 2-stroke was about the only widely available diesel option in sizes suitable for use in typical skoolies, and most school districts simply could not afford the extra cost. This is evident when looking at an older bus from the 70s, as you'll not likely find this vintage with a diesel. They're hard to find even from 80s-vintage buses.

The Caterpillar 3208 was soon rivaled by the debut of the 6.9 Navistar, but for many school districts, diesel engines were still too costly and did not make financial sense just yet. Even though the 9.0 had been available for years, even school buses using International chassis still used gas V8 power more widely until well into the 80s.

So although diesel has been the norm for quite awhile now (and I have a theory on how all this came to pass), gas power is far from unheard of in school buses, and for a long time, it was the standard. In fact, the 290-square-mile county I grew up in had 45 gas buses, all 2+ ton and largely (if not all) 64-passenger.

Most were Ford and GM built before each manufacturer's respective nose-style changes in 1980 and 1973, with a few Dodges of the same vintage and type when I started school in 1982. A family friend at the time was a mechanic at the county bus garage, so I knew more than most did about them.

It was common with Ford back then to offer their gas FT block V8 engines, the 330, 361, 389, and 391, in the incomplete F-chassis used by upfitters such as Blue Bird, Ward, Carpenter, and Thomas. These FT-block engines were later replaced by the 370 and 429 gas V-8s in the 1980-up nose style.

I recall the county buying maybe five new buses from around 1988-1992, and I remember one diesel, an early-90s Ford that likely had the 6.6L New Holland, cheaper than the 5.9, I imagine. The bus I rode my senior year of 1994, was an old familiar gas Chevrolet C60 that couldn't have been any newer than 1972, still in use and little the worse for wear, aside from slightly worn valve seals. That should speak volumes for these old gas models.

Smaller buses on GM's P-chassis (later dubbed WorkHorse) were mostly gas 350s, a few were 454s, with a diesel option, mostly 6.2 / 6.5, some may have have even gotten the 5.7 Oldsmodiesel, available prior to 1982 in some GM pickups. Some of the P30 step vans got 4BT Cummins, but they're not that common and I think most of the P-chassis were strictly gas-powered. And most larger ones were as well until the late 80s / early 90s.

454s were not common in even these though, you'll see 454s much more widely used in RVs built on the P-chassis. The WorkHorse / P-chassis buses are identifiable by either a completely custom-built body by the coachwork manufacturer, or a cutaway Express / Savana / G-van cab with a fiberglass or steel bus body. But gas power is still quite common with these as well.

However, there were no factory 454s in larger, more common school buses on GM chassis. GM's 2+ ton C40-C70 chassis used a truck-specific tall-deck version of their gas big-block V8, in 366 CID and 427 CID, dating back to at least the early 70s, if not the late 60s. It was specifically built for higher-torque / lower-RPM applications.

If memory serves, this engine was still in production as late as 1985, some sources indicate the late 90s (likely dependent on the displacement in question). It was replaced with the 8.1 Vortec, though I'm not sure what year this came about.

Essentially, the Mark IV 454 and tall-deck 366/427 engines were put out of production in favor of the new Gen V model, which had its own version of one of the performance goodies favored by drag racers who had used the Mark IV -- a stroker crankshaft, which gave the Mark IV 496 CID, and the Gen V 502 CID. 8.0L, and 8.1L, respectively.

The 8.2L Detroit was an option when it became available, around 1980. Still, most districts clung to their gas engines due to budget constraints. It just didn't make financial sense to embrace diesel power just yet -- and let's face it, the 8.2 was far from a shining example of the benefits of diesel power. Interestingly, the Detroit 8.2 displaced 500 CID, so I'm not sure why the 502 was dubbed the 8.1 and the 500 CID Detroit was dubbed the 8.2. But I digress.

So, you see, it really depends on the era and type of bus you're talking about, because gas power is far from unheard of in a skoolie, even the larger ones.

As to how decades of skoolie gas power gave way to diesel, this is just a theory, but historically, gas engines were just cheaper to buy, maintain and repair. However, that would be soon be changing, as emissions controls were quickly becoming mandatory even on some commercial gas engines by the mid-80s. Before fuel-injection became standard on gas engines, this was achieved partially by using solenoids and servos to adjust fuel mixture and idle speed on electronic-controlled carburetors, which worked fine until they didn't.

I imagine dismantling and rebuilding a $500 carburetor to replace a $5 solenoid didn't make financial sense when servo and solenoid failures were common at 5-10 years old. And fuel-injection would not be available on many large commercial gas engines until well into the 90s. So presumably, rising maintenance and repair costs, the increasing relative and comparative simplicity of a mechanically-injected diesel at the time, and exemption from emission controls are why many school districts began asking for diesel power in the late 80s to early 90s.

Diesels and some larger commercial vehicles were still exempt from emissions requirements back then, so many school districts began asking for diesel power. As an added bonus, diesel fuel was still cheap at the time because (as sources indicate) it was nothing more than a waste by-product of refining other petroleum products that just happened to be useful as diesel fuel.

So, at the time, diesels were beginning to make more sense because they lasted longer, they were more efficient, and the fuel was cheaper. So by the early-to-mid-90s, a lot of school buses were being built with diesel engines, whether on incomplete chassis or purpose-built.

That changed again in the mid-2000s when emissions control became mandatory. And emissions-formulated diesel fuel became mandatory. And unfortunately, emissions controls have proven to be far more of an issue on diesels than they ever were on gasoline engines. Having been an over-the-road tractor-trailer driver for a few years, I've experienced these problems more than most.

I saw a brand-new 2019 Blue Bird Vision on the block at CoPart that had been damaged in transit prior to delivery. 2+ ton chassis, 54-64 passenger, Ford V-10 gas powered. So school districts are obviously starting to review their options. Don't be surprised to see more gasoline-powered buses in the future.

In summary, the same maintenance issues and rising costs of emission control systems that would seemingly appear to have caused the switch from gas power to diesel power in the first place, now appear to be causing a reversal. I think it's safe to say you can expect gas power to make a comeback in the years to come, if DPF and DEF systems continue to prove as troublesome as they have in recent years.

I suspect Ford and GM have seen this coming, and that may be the reason that production of Ford's V-10 continues after publicly 'de-emphasizing' V8s. Likely the reason GM spent the money to upgrade and improve their gas V8s to create the Gen V family. I don't think gas power ever really went anywhere, we've just seen periodic shifts from one to the other due to dollars and sense, and budget constraints.

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Old 05-18-2020, 06:28 AM   #2
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Year: 1971
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I will add to this Internationals line up of gas engines. From around 1960 till early 70's the 304 and 345 were the common school bus engines in an International chassis. A sales ad I have from 1972 shows both these engines, and available with either a 4 speed or 5 speed manual trans, or a 4 speed automatic. Both of these are know for the longevity. High nickel content in the iron for the block gave long life, and also gear driven camshafts made worries about timing chains failing a non issue.

The 392 V8 was a problem child and also not an option in the early years. It had cooling troubles that caused hot spots in the cylinders and this would cause pre ignition. My bus did have one of these in it, and after two melted pistons I took it out and put a 345 in. I am not sure of the exact year but 1973 or 74 they made an "Improved cooling" 392. These are good dependable engines. You can tell the difference by the cooling tubes on the front of the engine. The improved cooling ones have the tubes going from the water pump to the block just below the heads. The old style have the tubes going into the heads.

The 6.9 International diesel is what replaced the gas engine starting in the 80's as an option. By sometime in the mid 80's all gas engine were dropped
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Old 05-18-2020, 08:34 AM   #3
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Conventional nosed school buses were built on MD chassis because body builders saw no need to reinvent the wheel. GM, Ford, Freightliner, and International all had options available that could be made into a school bus.

The transit model buses, however, are typically built in house by most body builders from the ground up. Most will still use the same components from the MD chassis lines to reduce costs, but the chassis design and manufacturing is all done in house.

Diesel engines slowly phased out gas engines for a host of reasons. The fuel was cheaper, they lasted longer, had more torque/hp, got better fuel economy, and had lower maintenance costs.

I don't know if gas engines were ever truly eliminated from the line up. But the last gasoline engines that I know of were the 454/496 in the chevy/GMC school busses that ceased production in the mid 2000's. I know bluebird used ford v10's occasionally throughout the years since, but they were typically propane or natural gas powered.

It's predicted that gas engined buses will make a comeback though. Gasoline now is cheaper then your ULSD diesel fuel. Maintenance costs on a gas engine are cheaper then their diesel counterparts, especially when you factor in emissions equipment. Modern gas engines can last as long as a diesel engine. The multi-speed automatic transmissions used nowadays closed the performance gap that was present between gas and diesel. And finally, a gas engine is a cheaper option to purchase then a diesel engine.

Don't be surprised if more new buses will come as natural gas powered too. The initial cost for setting up the district is high, but the fuel is dirt cheap thanks to the boom in production from fracking.
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diesel, engine, fuel, gas, power

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