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WILDEBILL308

Not Bad Mileage For Running In 5th Gear

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Well got back from Fredericksburg Texas yesterday. Short trip only 469 miles round trip. Went down the back roads going and coming back picked up I35 at Belton. I filled up and checked my mileage today 8.496 mpg. I learned that I wasn’t driving fast enough. I ran about 55 going down and on the way back on I35 I was running 60 –65. I was watching the tach and noticed that I was running lower rpm at 60 than at 55. Apparently I wasn’t going fast enough to get it to shift into 6th at 55. I was running in economy mode all the way.

I am wondering if anyone else has noticed this happening on their coach. This is a 2003 Bounder 38N 300HP Cummins with Allison 6spd. The more I drive this coach the more I am learning, I almost have a 1000 miles on it since I bought it. By the way I like my Kroger fuel points my price for diesel was $3.296 lots better than it has been.

Bill

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What you experienced is somewhat normal. Each coach will very a little. The shift points are set in the computer which is spec by the coach builder. It is determined by H P, weight, tire size, gear ratio. Mine shifts into 6th at 56 mph. I have a 32 ft with a ISB 275 towing a 1/2 ton Silverado. The last time I fueled up after going 871 miles I got 10.93 mpg.

Running slower in 5th could yield better mileage than faster in 6th gear. If you use a Road Relay or similar reader you can adjust your driving on the fly for maximum mileage.

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Click on the link at the bottom of this post on the Diesel RV Club website. The document was written by Caterpillar Corp, but applies to all heavy vehicles.

What you will find is that HP demand goes up rapidly as speed goes up. Yes, you could actually be getting better MPG at lower speed in a lower gear.

http://www.catrvclub.org/PDF_Docs/Understanding_Perf.pdf

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