Gas Mileage, Tune-up?, Real Numbers

[Bus Busted]

   Ok, I have about 10 trips on my 1984 Eagle 10 now. The conversion is at the starting point and light weight. No surplus water (7 gal camper potty) and two coolers for food. Does have a camper stove and reg sink draining into a 5 gal bucket. Like I said, light. The runs have been from Indianapolis to Nashville and back. Running speed 75-80 mph and 18-19 on the tach (looks like 22 @ full petal). 8 of the trips I filled until I saw non-foaming fuel in the filler. I show that I am getting around 13 mpg, 12 when the bays are 1/2 full of heavy stuff. It is a 6V92 blower and turbo, 5 spd manual. The tires are 11R24.5 running 90 PSI. I do not know the injectors or timing at this point.

  When I first started figuring gas mileage, I was sure this was wrong. Now I have made this run enough that I keep getting the same mileage and I'm sure it's right. I think I need a tune-up or something, because it takes longer to start than most posts I read say it should. On a damp or cold day it takes 6 to 8 10sec presses on the button to get going and 2 if I use either. I get a bit of smoke during this time, but it clears up as soon as the motor starts running. If I restart it after a short trip I get no smoke and it fires up on the 1st press.

  I would like to take it in for a tune-up, but not sure if my mileage will take a hit (can that happen?). Also is anyone else getting this mileage? I thought these got around 6-10 mpg. I had planned to get a tune-up and switch trans to an auto to make it easier for others to help with driving, but if that gets me half the mileage I'll just do all the driving myself. Also not sure how heavy I want to go on the conversion if that will kill the mileage too. Any thoughts? Let me know. Thanks, Jon

[Bus Busted]

P.S. I don't believe in "Bus Miracles" so if this is not normal for this setup, are we looking at worn rings and bearing causing low running resistance? Blocked injectors reducing my power and starving the engine for fuel? Heat looks ok and the power feels good. All other gauges look good too. Just some thoughts.

[rv_safetyman]

Jon, that mileage seems very high to me.  Most Eagles get less than 10 MPG when lightly loaded - most well below.  Of course, road conditions (think hills), start and stop, speed, and wind can have a huge affect.   If your are really driving 75-80MPH, your mileage seems even more unrealistic to me.

Something sounds a bit "off" with your MPH and RPM.  The two typical rear end ratios in an Eagle are 3.36 and 3.73.  With the 3.73 you should be at about 70-72 MPH at 2100.  With the 3.36 you should be at 79-80 at 2100. 

I would check the odometer against the mile marker signs to make sure that it is giving you a reasonable value.  Check it over at least 10 miles to minimize the error.  Checking MPH against a GPS does not necessarily guarantee that the odometer is correct (I have seen odometers off by a fair amount and the speedometer pretty close).

If you verify that the odometer is close and you check the fuel over several fill-ups, then you have a great running bus and you should probably not mess with it.  Good power, minimal smoke, quick starting, and reasonable oil usage are all signs of a good engine - not one that needs any work.

A tune-up is basically "running the rack".  The folks who know how to do that correctly are getting small in number.  No need to run the rack unless you have some symptom and it does not sound like you do.

Jim

[luvrbus]

Leave it alone Jon all of Freedoms Eagles got good millage they were set 315 hp, 2300 rpm with 3:73 rear gears and a 5th over transmission good setup for fuel mileage  

good luck

[robertglines1]

Ck your block heater.  Might be bad.  Been cold in Indy    My 8v92 still starting rite up in E'ville w/o plugged in.   Bob  by the way  5 mpg here------ 6 at 65 mph.towing 36100 plus 3400 for towed

[rv_safetyman]

Clifford, I was not aware of a 5 speed manual transmission that had OD that were used in Eagles.  Interesting.

Jim

[luvrbus]

Freedom never did the standard Eagle stuff Jim even the Cummins engines in his model 15's and his 35ft model 20's with the Cummins

good luck

[artvonne]

  So to "slightly" highjack this thread, what is the best tuning for a detroit and best rpm to get the best economy? Is the turbo adding any mileage?  My understanding of "sweet spot" is the rpm that allows the fuel charge to be fully consumed at the point the exhaust valves open. Too fast and your blowing it out the exhaust, too slow and its not doing enough work, either side of sweet is less efficient.

  I remember this old Buick Stationwagon I had when I was 19. 455 V8, it had a hard time getting much over 4 MPG. Its amazing to see a Bus get over 5, 10 seems outragous, 13 is just about enough to make ya do back flips

[thomasinnv]

Artvonne, there definitely is a sweet spot. If I hang around 55 I actually get less mpg and produce more heat than say at 62 to 65. I believe because the engine is turning much lower rpm and not pulling enough air through the blowers to keep it cool, and maybe just below the torque curve of the engine?? If I run @ 75 all bets are off. Heat again begins to climb, and mileage goes out the window. (well, more out the window then normal).

[RJ]

Paul -

IIRC, the "sweet spot" for the 8V71s is 1700 - 1800 rpm running on the flat, w/ or w/o a turbo.  Roughly 1900 pulling a grade w/ no black smoke out the exhaust.  Black smoke = time to downshift.  6V92s seem to like 1800, 8V92s are happy at 1600 -1700.

Turbo's biggest benefit is maintaining sea-level HP as you climb RockyTop.  Also allows you to go further on a grade before having to downshift, so theoretically fuel mileage should be slightly better, but usually isn't because of the "Home Improvement Syndrome." 

FWIW & HTH. . .

[uemjg]

@ Paul: Since I also have an 8v71 I have a couple questions:

1. Is that "sweet spot" different from 1 motor to the next?

2.  "                      "    different from MCI or Eagle?

3. Since my bus doesn't have a tach, where is the best place to attach a tachometer?

[artvonne]

@ Paul: Since I also have an 8v71 I have a couple questions:

1. Is that "sweet spot" different from 1 motor to the next?

2.  "                      "    different from MCI or Eagle?

3. Since my bus doesn't have a tach, where is the best place to attach a tachometer?

  My understanding of the "sweet spot" regarding diesels, relates to the speed of the flame front after ignition, and the full consumption of the fuel charge. While bore would have some effect, the main factor is the stroke, or, the distance the piston travels from top to bottom. Matching the piston speed to the flame front speed, so that the entire air/fuel mixture is consumed just before the exhaust valves open will put the greatest amount of energy to work. Running the engine too fast opens the exhaust valves too early, allowing high pressure gases to escape and is a loss of energy, as is turning so slow the charge is consumed long before the piston reaches full extension/valve opening.

  Other factors are the burn rate of the fuel itself (Cetane), as well as injection timing. I once had a book on tuning the old 6.9 Navistar engine that gave different injection timing figures for fuels with different Cetane ratings, but that was back when you could find Cetane ratings of pump fuel. Back then they timed diesels for power and economy, now they time them for emissions, often making them so inefficient they offer no real gain over a gas engine. I guess if one wanted to dig deep enough you could find the burn rate of the fuel and calculate the time it would take to cover the stroke distance and calculate rpm off that figure. But im lazy and just figured I would ask.

  When Hub Van Doorne invented the continuously variable snowmobile transmission (Variomatic), in 1958, the dream was always to connect it to a constant speed diesel where it would achieve its greatest efficiency. Its just never really quite worked out.

[trapper]

Getting back to the original question. If your bus is hard to start after it has sat for a day or two it could be that your fuel system has a leak and you are getting air in the system. This will cause it to take a while of turning the engine over in order to reprime the system. The next time you want to crank it and you feel it has been long enough that it will not start immediately watch the exhaust pipe while you crank it. If it is white smoking the whole time it should be getting fuel. If it either is not white smoking or smokes just a little for a few seconds and then stops you probably have air in the system.

[demodriver]

This bus he is asking about is my old eagle. I never got anywhere near that kind of milleage. The best I got was 10 mpg at around 65 mph not sure why it would increase in milleage by running it faster/harder then I did.  As for the starting. I was always told that if a diesel starts right up its wore out.  This bus has pertty low milleage compared to most and always started as it should IMO. Granted it wasnt very cold when I had it.   

I am sure that the engine is fine and I wouldnt worry about a tune up on it yet.  just my opinion

If you want your money back I would be more then happy to buy it back 

[HB of CJ]

Thank you all....for awhile I believed!   HB of CJ (old coot)