6.9 motorhome giving new grief

[Cubey]

I'd say so. Cubey has a 1985 RV. I think it's 27 or 28 feet. I think that he said that he gets about 7MPG after installing a new Motorcraft fan clutch.

I think was a combination of factors.

- New fan clutch
- Winter blend fuel began showing up (early October)
- Fuel system got dirty (for a time) from using the rear tank some around that time when I was messing with the FSV.
- Mechanical fuel pump weeping fuel to the ground

Below are all the fuel ups since we did the fan clutch.

The first 13 fill ups (using only one fuel tank, so I frequent fill ups were needed) were about 8.04mpg combined city/hwy. (I just calculated it)

Then I used HotShots extreme diesel treatment around the last week of December, and I think that hastened the demise of the old original mechanical fuel pump, which began leaking pretty heavily. You can see it instantly drop a lot after the 12/30 fill-up. It was going bad already, but at a much higher rate after a treatment. It got to the point where I could see it dripping on the ground at idle. Maybe it was just a coincidence that I used hotshots when it got really bad?

The last 5 fill ups were down to about 7.44mpg, but that was probably due to the lost fuel on the ground getting worse and worse. Of course now it has a Holley red electric pump conversion that I did around February, but I haven't driven it enough to warrant a fill up. Hence the last one being on 1/25.

Last summer, it was getting as high as 9-9.5 on on the highway, but again that was before the new fan clutch, summer fuel blend, and fuel pump wasn't leaking fuel on the ground.

If he has an E40D, then that might be why his MPG is 12. Dunno what rear end he has either, and how heavily he has it loaded down with gear inside/liquids (water, LP). Mine has an insane cabover that sticks out further than almost all other Class C's too. Not all RVs have a big built in generator too, so that's another couple hundred pounds on mine. His timing might be set better than mine too. (It's all screwed up now with the Holley pump putting out 5-6 psi at 55-60, and being it's top speed now!)

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[gjabrown]

Interesting that your mileage is so low. We just completed a trip to the end of our island and back and did 10 MPG per US gal with a 26 ft class A on an E450 chassis with a 6.8 V-10. I thought that diesels were supposed to get better mileage​

 

[Cubey]

Interesting that your mileage is so low. We just completed a trip to the end of our island and back and did 10 MPG per US gal with a 26 ft class A on an E450 chassis with a 6.8 V-10. I thought that diesels were supposed to get better mileage​

It might be the timing or injectors. So much is/was original on it. I would be happy with 9-10mpg for as big and heavy as this thing is. The cabover sticks out almost as far as the front bumper, but it is in a V shape at least to help with airflow.

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I got about the same MPG in a 19ft 78 Dodge 1 ton class B van years ago. (5.9L 360, A727 3 speed A/T) Some fuelly records from it. I ended up not ever using it beyond about 5 months. Such a waste.
http://www.fuelly.com/car/dodge/b300/1978/cubey/312834

Maybe it was something in the carb that made it get such poor MPG? Beats me. I was thoroughly disappointed. It got about 5-6mpg city. I sunk too much money into it and lost so much when I sold it, then regretted it a year later and wished I still had it. Oh well. That's why I am clinging to my F250 while also having the RV.

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A newer V10 E450 is gonna have at least a 4 speed A/T with OD and computerized controls for everything (fuel, air, timing), helping the mileage.

 

[IDIBRONCO]

Interesting that your mileage is so low. We just completed a trip to the end of our island and back and did 10 MPG per US gal with a 26 ft class A on an E450 chassis with a 6.8 V-10. I thought that diesels were supposed to get better mileage​

His C6 transmission probably doesn't help much.

 

[Cubey]

His C6 transmission probably doesn't help much.

So many factors can hurt MPG and they pile up if there's problems like the old leaking fuel pump, winter fuel, etc.

A lot of people don't drive around with 25-30 gallons of water since usually stay in RV parks or campgrounds, so they get water when they get there and dump it before they leave. I drive around with it at least 95% of the time since I stay off grid most of the time.

Since I have a diesel chassis engine and a gasoline generator, the RV maker put a gasoline tank for the generator instead of installing an LP powered generator. (LP gens by Onan existed in 1985, they just didn't opt for it) So that's more weight for the little steel tank and gas in the tank.

I got the fiberglass air dam put back on since I've been back. I left it behind since I was lazy and just ready to go last time, didn't wanna spend a few hours messing with it. Not sure why it needed cutting the fiberglass to make it fit properly again since nothing looks bent on the bumper or fenders. That's why I left it behind. I put it on but it cracked mounting point from being under pressure from pressing against stuff under the bumper. This time, I made the existing cutouts in the air dam larger to clear the stuff and now it's fine. Maybe it'll help a fraction of an MPG since it'll keep some air from getting under the RV.

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