Can I drive in 3rd gear indefinitely?

[Scott & Heather]

So since we have not figured out what is wrong with our cruise control yeah, there are times when I am comfortable just driving at 60 mph down the interstate on a straight shot. Is there any harm in putting in third gear and just keeping the pedal floored for an indefinite period as long as I'm not over speeding the engine on a downhill?


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[muldoonman]

Don't know Scott and one of the smart guys will get back,  but I'd put that puppy in 5th and get there faster with the same logic. That being said, don't think bumping that governor doesn't sound like a good idea.

[Scott & Heather]

Interesting. I always thought these things pretty much ran full boar all the time anyway. At least I think they do in generator applications. Maybe I'm washed up about it. It's just easier driving hours a day with the pedal mashed versus regulating speed all day. Sounds trite but we are driving 13,000 miles in the next three months so it actually does make a different in driver comfort


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[RJ]

Scott -

Sure, you can run in third gear indefinitely.

But watch your fuel mileage plummet in the process.

Unless you don't care about your fuel costs, of course.

I don't have a cruise control, and have driven Tortoise over 35K miles in three years.

I never had a cruise control when I worked in the charter business, driving 80K+ miles a year.

Thousands of Greyhound, Trailways and how many other bus company drivers have driven without one for years.

Until you take the time to figure out why your cruise control isn't working, drive like you don't have one.

Just watch the tach - a lot easier to keep it w/in 100 rpm of your desired speed vs watching the speedo. 

Unless you've got a nice digital speedo - like what's on your GPS if you poke around a little.

Many other busnuts would be thankful that that's the only issue they have with their bus.

FWIW & HTH. . .

[luvrbus]

Interesting. I always thought these things pretty much ran full boar all the time anyway. At least I think they do in generator applications. Maybe I'm washed up about it. It's just easier driving hours a day with the pedal mashed versus regulating speed all day. Sounds trite but we are driving 13,000 miles in the next three months so it actually does make a different in driver comfort


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They don't run full bore on generators most all industrial application have 1800 rpm governors max so do most fire trucks pumper engines with the 8v92 

[TomC]

As engine rpm rises, so does the friction-meaning just to turn over the engine at a faster rpm takes more fuel. 8V-92TA is happiest cruising between 1,600 and 1,800.
Also, leaving the transmission in third (I assume an Allison transmission?) means you're going through a set of gears-which means some power loss, additional heat, etc. If you allow the transmission to shift to fourth (HT740), then you'll be in direct drive-meaning no gears are being used.
Over a long period of time, running the 8V-92TA in 3rd at say 2,100 will burn a tremendous amount of fuel (like 2-3mpg difference) than running the same speed in 4th at say 1,600. The most fuel efficient speed is right at 1,600.
When I was driving my first truck with 8V-92TA and 13spd, in overdrive (RTO-12513A-.86 overdrive), with 11R24.5 rubber and 3.90 rears, that gave me a cruise speed of 61 at a little over 1,600 (days of 55mph). Good Luck, TomC

[Scott & Heather]

Ok I see the light now. I thought these engines like higher roms and no lugging. Got some reason I thought running at 1600 rpm might be lugging it a bit. Ok, good info. That's why I asked. 4th gear it is. And I'll admit RJ, we are a bit spoiled. But I am absolutely getting my cruise figured out soon lol


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[Boomer]

You will maximize your fuel milage by doing just three critical things:

SLOW DOWN
DON'T IDLE THE ENGINE
OPERATE ON CRUISE CONTROL AS MUCH AS POSSIBLE

Tried and proven!


Funniest quote I ever heard was from Clifford.  "I drive fast because I don't have much time left"  LOL, LOL

[Scott & Heather]

This thread wasn't about mileage, it was more about what was possible without damage to engine or trans. Based on responses along those lines, I will refrain from long periods of 3rd gear runs


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[muldoonman]

The way mine is geared around 1700/1800 rpm's puts me at about 65 mph with this 755CR trans is my memory is correct. 12R 22.5 tires.

[bigred]

My bus man says the 8v92 is happiest at 1800 rpm ,As a matter of fact he says that any time I am off the Interstate to run it in a lower gear.He says they will live longer if you drive them like you are mad at them.I have found most of his info is pretty much on the mark!!

[TomC]

When I was driving beer and beverages up and down California, I was going either north or south on the Grapevine (I-5) everyday. I had my truck tuned up at Delaney and Ahlf in Bakersfield. Asked how to get better fuel mileage-said to drive the 13spd like a 9spd (don't split gears) and to upshift at 1800 and downshift at 1400. Got about .3 better fuel mileage and easily outpulled a couple of my buddies-one with a Cummins NTC400 and the other with a Caterpillar 3406B 400hp. Was rather satisfying to pass them in my "Yamaha".
92 series is completely different than the 71 series. 92 likes to run 1400-1800, 71 likes to run 1800-2200. Although my 8V-71 turbo'd and air to air intercooled doesn't mind lower rpm. On partial throttle, the V730 will shift at 1600 bringing the engine down to 1100 on shift. Full shifts are at 1900 (can hold it in with shifter). Engines have a finite life. Slower you run them, the longer they last. Caterpillar determines engine life by how much fuel flows through the engine. Good Luck, TomC

[Zephod]

I keep my schoolie in drive and foot to the floor on the interstate - pretty much like my work bus.


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[blue_goose]

There isn't much to the cruse control, why isn't yours working? 
Jack

[TomC]

I have a King Cruise control cable operating the gas pedal. Works well. Good Luck, TomC