Should our RV be getting only 7 mpg?
We have recently travel about 1000 miles cross country in an RV. Long story short is the gas mileage seems to be particulary bad on this trip. My SO swears back before my time on the scene the RV got something like 14 miles per gallon. And that was with towing a car, probably driving a bit faster, running the generator (and both the AC units that run off the generator) and smidge more stop and go traffic to boot.
THIS trip we are averaging more like 7.5 give or take. I've never bothered to keep track of our mileage on all the shorter (couple hundred miles tops) trips we do fairly frequently, so I don't know whether this a new thing, a gradual thing, or my SO's memory of the good ole' days is just wrong.
One thing is different. We are now towing a Jeep Liberty with 2 canoes on top rather than in the ole' days which was just a smaller more streamlined Saturn car without boats on top. But the Jeep and canoes still appear to me to be mostly in the "slipstream" behind the RV. I could see it increasing the drag a bit more than the old Saturn, but I can't imagine it dropping the gas mileage by 50 percent.
The RV is a 35 foot class A motorhome. Model year 1997. It has the older "basements" so I supect it is not quite as tall (and therefore draggier) than newer models. It has 37,000 miles on it. The engine is a Chevrolet 454 7.4 liter V8 Vortec engine with SFI (which I guess is some sort of fuel injection system).
We are typically driving it in the 60 to 65 mile an hour range. We left from the south and are now in the midwest so its not like we are climbing mountains either. Its mostly been interstate or good highways so not lots of stop and go traffic either. If I assume worst case fuel consumption for the generator running full out (according the manual), the mileage is more like 8.5 miles per gallon.
So, given all this, is this the kind of mileage one would expect?
One thought I've given is to try a fuel injector cleaner before we head back in a few weeks. Any recommendations as to brand/type and hints on using it? Or is using it a BAD idea? Even if it helped just a bit on mileage it would probably pay for itself on this trip alone.
Any hints on what else to possibly look at? I could probably do the air filter, spark plugs, and spark plug wires myself before heading back. Maybe the generator is REALLY sucking gas?
thanks for any hints or input!