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Old 03-16-2015, 12:14 PM   #1
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1986 34.5' Airstream 345
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345 Motorhome gas mileage

We have now -more or less- finalized the re-build of our 1986 classic 345 mo-ho. one of my first trips after rebuilding the failed torqueconverter was a 450km (about 240 mls) trip, all on "flat" german freeways, speed between 60 and 70 miles. almost with cruisecontrol, at nighttime.
i filled up tiotal the gastank and refilled it about 350 km (200mls) later again.
I WAS SHOKED !!!! i used 44 litres of gas per 100km (thius is the way we calculate gas consumtion in Germany), transformed in mpg, means 5.3 mpg!!!!
PLease consider, gas is significant more expensive here than in the US, about 5.30USD per Gallon...!
While we drove our rig from IOWA to the port, where we shipped her to Germany, we had about 27 litres per 100km, means 8.7 mpg. i was satisfied, we move a big round belly with a strong engine, if you want to play, you need to pay...!
But this trip here in Germany was terrible. i went into a Chevytruck shop, they checked carefully timing, exhaust emissions, vacuum lines, just some minor "defects" from some closed vacuumlines for EGR, and airpump, thatīs it. Engine runned perfectly and powerfull, i had no "fat" smell from rich carburetor, nothing seems to be wrong.
Here is my question:
What is an average gasmileage you get? The riug is equipped with a Banks powerpack, brandnew, sparks, cables, oil tune-up, all is good or new.
After we broke the Stock-Torqueconverter, we replaced it with the Allison HD 545 converter, itīs allmost the same, but but much more dependable.
what happens here, i have absolute no idea...! is 9 mpg realistic, with our baby, considering the Banks system and a cruisespeed of 60-65 mls/h.
Just let me know.
Have save and blessed trips!

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Old 03-16-2015, 03:51 PM   #2
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This thread:

has many, many posts with gas mileage figures. For our part, we started out at 4-5 mpg, went to 7-8 mpg after a carburetor rebuild, and are at just under 7 mpg about 10,000 miles since the last tuneup.

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Old 03-16-2015, 03:55 PM   #3
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I would think 7mpg would be about average I had a old86 southwind that's what it got didn't change 60 or 70 uphill or down I figure that's all could go through the 7/16 fuel line
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Old 03-16-2015, 09:07 PM   #4
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This is just a guess and I'm sure Shepherd57 will be able to give a better diagnosis.

Just curious....what RPM were you running at on your trip in the states BEFORE you fixed the transmission compared to the trip in Germany? If the rpm's are significantly higher, say 500+, then maybe the torque converter is not locking up into the overdrive position. This could easily account for the lower mileage.

If this is not the case, then I'd suggest not smoking anywhere near the back of your rig close to what looks like puddles of water.

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Old 03-16-2015, 10:28 PM   #5
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My '83 310 ran at 8 to 9 miles per gal usually, but at speeds of 60 to 70, it could easily drop into the 7 MPG range. I generally drove it under 60 mph.
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Old 03-17-2015, 06:20 PM   #6
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I get from 6.5 to 9mpg pulling a Suzuki Vitra (about 2800 pounds) at 64-75 mph. Not great but good knowing when I first got it, 4-5 mpg. Then the only way to go fast was to get in tight behind a semi.... Really tight!
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Old 03-17-2015, 08:32 PM   #7
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We have 115,000 miles on our 1992 350 classic xl and get 6.5 in the mountains and 7 in the flatlands.
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Old 03-17-2015, 10:14 PM   #8
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I agree with most of the above mpg readings on my 350 particularly the advice to keep the speed between 55 and 60 mph (or the kph equivalent) and stay close to 3500 rpm. not exactly autobahn stuff so stay on "Landesstraßen"!
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Old 03-18-2015, 04:29 AM   #9
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Thumbs up gas mileage

Hi Chriscraw,
i also have to stay at 55 - 60 mls per hour, even on "Autobahn" here in Germany. The speedlimit for ANY vehicle with more than 3,5 ton GVWR / 7000lbs is limited to 80 kilometres per hour. thatīs about 50 mp/h.
You may drive the same speed at "Landstrasse", if not limited to 70 km.(very often!)
The cops are strict here, if you get caught with more than 90 km, about 60 mp/h, it will be VERY expensive...!
Thank you ISUZUSWEET, i don`t remember the rpm in the states. here it was 3000 rpm, i guss, itīs a few month ago i drove her last time. How can i check, if the converter gets clutched into overdrive? What is the "normal" rpm at 55-60 mp/h? i also checked for gas leaks, but there was nothing, no smell, nothing. She runs just great
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Old 03-19-2015, 12:37 PM   #10
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1986 34.5' Airstream 345
Grefrath/ Germany , NRW
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gas mileage classic 345

Dear all,
i have checked today with the supplier of the torqueconverter here in Germany.
i have relized, the converter (Allison HD 545) is compactible with the TH 400 tranny, matchs flexplate/flywheel 100%. Also it is a much more dependable unit with welded elements inside, but it is NOT equipped with a "lock-up"...! Nobody told me before, that the stock converter has a "lock-up"!
The mechanic asked me, what was the avarage rpm., while we drove cross USA with the old stock-converter, but i do not remember this, it is a year ago now.
Is there any owner of a standard "1986 classic 345" with 454V8 here, who can tell me the rpm with stock converter at 55-60 mp/h ??
Ours was modified with the "Banks-Powerpack", this lowers the gasconsumption, but not rpm, as far as i know. There is a vacuum switch on tranny, who allows a higher shift speed.
i guess, i drove the rig with 2800 rpm till 3000 rpm, but i am unsure about.
Thank you very much for any support.
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Old 03-19-2015, 01:36 PM   #11
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At 62 mph my rpms are about 2700. Allison at545 but with the Isuzu diesel.
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Old 03-20-2015, 08:01 AM   #12
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1986 34.5' Airstream 345
Grefrath/ Germany , NRW
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Posts: 202
gas mileage

Just to make it clear again:
we have the stock 454 V8 Chevy gas engine, with standard TH 400 tranny.
We only changed the torqueconverter, by using an Allison 545 HD converter.
A technician from "Jasper.engines" told me, these converters are more dependable, than the stock converter. He did NOT tell me, the Allison converter has no "Lock-up"...
Please, if anybody has a 1986 "345 classic", or "325 classic" (dual pump) with gas engine and standard tranny TH 400, please let me know:
What is your rpm at 50 mph, at 60 mph and 65 mph, maybe.
Thank you.
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Old 03-20-2015, 01:58 PM   #13
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The standard TH400 does not have a lock up torque converter. As a result the rpm at any speed can vary quite a bit with the load. If you are going up hill or accelerating the rpm will increase compared to road speed.

I am running the Allison torque converter because it is a better built unit. I also have some newer clutches and bands from a 4LE80 trans that help the TH400 a bit.

If you want to drop the rpm you can change the rear axle ratio but then you sacrifice low speed performance. You will really see torque converter slip during acceleration from a standstill. Another option is to add an overdrive unit such as a Gear Vendor which you probably know as a Laycock used in many English and other European cars. This will give you six forward gears to play with. A third option is to swap to the newer 4LE80 trans with converter lock up. You will need to install an aftermarket computer circuit to operate the system.

I have a 1982 28' with the Isuzu diesel and TH400 trans. I added the Gear Vendor Overdrive unit and I love it. I drive at about 62 mph and the GV drops rpm from about 3000 to 2400. Fuel economy will vary from 11 to 15 mpg depending on city, highway, mountains, and most important, how enthusiastically I'm driving.

There is no simple solution and whatever you decide will not be cheap. How many miles you drive is a consideration into whether it is worth spending money to up grade or be happy with what you have.

Good luck.
Cheers, Dan

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Old 03-21-2015, 04:33 AM   #14
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1975 29' Ambassador
1986 34.5' Airstream 345
Grefrath/ Germany , NRW
Join Date: Jun 2013
Posts: 202
gas mileage

Thank you "Smartstream" for your details answer.
If there is no "Lock-up" in the stock converter, and the only change we made is from stock to the Allison Converter, WHY is the gas cosumption that high now ?????
Any idea ???? Your gas mileage with the ISUZU Diesel is wonderfull, will never get this with the V8 gas Chevy. Also the rpmīs you drive at highway speed seems to be different to the gas model, am i correct? Anyhow, 5.3 MPG is more than terrible, WHERE is the default..?!

I also decided to buy the "Gear-vendor" under-/ overdrive unit, but the costs are very high. Not only the purchase, but also the labour here in Germany and shipping of the parts. In addition to this the Euro (€) became very weak and this will raise the costs again.
We donīt drive a lot per year, because of missing time. just about 4000-5000 mls...!
My thought was to install a LPG system from IMPCO, this is very interesting here, because the LPG is just 1/3 as the price of the gas.

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