[VAL] Gas mileage

[John Sellers <sellersj@xxxxxxxxxx>]

Gang,

The list has been pretty quiet lately, so maybe now is a good time to
ask a question I have been wondering about.  What kind of gas mileage
can we expect to get towing an Airstream, especially one of the smaller
ones?

We have been towing our 16-foot 1960 Pacer for two seasons now, and I am
a little surprised that we don't get better mileage.  More details
below, but briefly, our half-ton 4WD pickup truck, depending on load,
terrain, wind, etc. gets anywhere from 16 - 20 MPG on the highway
without the trailer, but only 10 - 11 MPG with the trailer.  That's no
better than we got with a Rockwood 22-foot motor home, at 10,500 pounds
GVW and the aerodynamics of a barn.

Here are the details:  We are towing with a 1994 Chevrolet K1500 4WD
half-ton pickup (with a fiberglass cap), gas V8 (5.7 liter EFI),
overdrive automatic transmission, 3.42 rear axle, and factory towing
package.  Truck configuration is plain cab, long bed, 6,000 pound GWVR. 
Truck tires are Goodyear Wrangler LT 225/75R16 inflated to the
factory-recommended 50 PSI.

I have always been impressed by the mileage that the truck delivers by
itself.  I'm not exaggerating when I say that I have averaged 20 MPG on
several cross-country trips, admittedly lightly loaded and probably with
a tailwind.  16 MPG is more typical with a heavy load.   Not bad for a
6,000 pound GVW four-wheel-drive vehicle.  (Running in 2WD on the
highway, of course.)

According to information in the VAC archives, the 1960 Pacer weighs 1750
pounds empty, and I would guess 2,500 loaded, at most.  There's not much
in a Pacer - 15 gallon fresh water tank and 7.5 gallon black tank, no
water heater, no A/C.  Not much storage space, either, which is why the
truck is usually pretty well loaded when towing the trailer.

Tires on the Pacer are  the original type 7.00-15 LT bias ply, except
that the trailer originally carried Load Range C and we are running
Firestone Trans-Rib Load Range D.   We have also been carrying 50 PSI in
the trailer tires.  (At full inflation for Load Range D, 60 PSI, each
tire is rated for 2,040 pounds, darn near the weight of the whole
trailer.)

The Pacer tows very nicely.  Except for seeing this big shiny thing in
the rear view mirror, on level road it's easy to forget it's back
there.   So howcum  this combination going down the road at 8,500 pounds
combined vehicle weight and slick aerodynamics doesn't get any better
mileage than the old Rockwood motor home on a GMC van chassis with the
same 5.7 liter V8 (carbureted, not EFI) and the drag coefficient of a
sign board?

One obvious difference when towing is that I am running the transmission
in D, not overdrive, and the engine is turning up probably 25% higher
revs for a given speed.  This is somewhat offset by the fact that I
drive slower with the 'Stream, trying to keep it down to 55 - 60 as
opposed to whatever the traffic will bear when running without the
trailer. The owners manual advises against towing in overdrive, but it
might save some gas.  Anybody have any experience with it one way or
another?  I'm a little reluctant to try it.  Ruining the transmission
would cancel out a lot of gas savings.

I should mention that I frequently feel the trailer tires and hubs at
rest stops to make sure nothing is running hot. They have never been
much warmer than ambient temperature.  This seems to rule out a problem
like axle misalignment or the trailer brakes dragging.

Would be interested in hearing other people's experience with gas
mileage.  Anything I should be doing to improve mileage without major
capital investment--like a diesel tow vehicle?

See you down the road,

John & Barb Sellers
WBCCI/VAC #1587
1960 Pacer
Dayton, Ohio