hi,
I would say ....a 'weak maybe' ....
or 'not too likely.'

However ...
it is always good to add a good fuel injector cleaner to the gas tank now
and then.
I wouldn't think STP is an especially a good one ...but more on the hyped up
side.

I do think Lucas brand fuel injector cleaner is good.
I also sometimes add a bit of Marvel Mystery oil...says fuel system
lubricant on the bottle...
Or even some B-12 Chemtool
or ..
here's a very high quality one I believe .....Seafoam.

as long as you 'do something' to treat the fuel and 'try' to clean the
injectors now and then.

it won't make up for really lousy injector spray patterns ..
and I would not expect a fuel milage improvement really.

Vanagons don't really get out of tune to me.
Sure ..they get ancient say ..plug wires that need to be replaced..
and any non-Bosch distributor cap is an automatic thing to replace...
and  I don't find that the spark plugs wear much at all...

the can develope fuel injection problems of course ....which need to be
corrected properly.
That's what really goes wrong on them in terms of proper running ..
the tune-up parts per se ...last really really well...if Bosch parts.

It's extremely important that it run fully up to temperature , like on the
temperature gauge.
also winter time very short trips are just hell on engine wear and fuel
economy.

a tired oxygen sensor can lower fuel economy too.
so can the throttle switch not making contact at idle. ..which is very
common - I find those not making contact 'usually' ...like 8 out of 10
waterboxer vanagons I work on.

on some ..the switch can't reach adjustment anymore ....but that can be
fixed sometimes..
or the switch is just too corroded to adjust any more.

so ....sure ..deffenitely put in a   QUALITY fuel injector cleaner now and
then..
but don't expect a big change ..
it's more of a preventative treatment really, in my opinion.....and should
be put in once or twice a year.

last august I got 20 and 21 mpg on a road trip .....1.9 waterboxer with
fresh valve job and running nigh perfectly ....cruising at 60 to
65...........going up to 80 a time or two going downhill.
 85 Westy, manual trans ..

I thought that was pretty good. No complaints there.  Fuel economy should be
better in high ambient temps and worse in cold temps.  I only run unleaded
regular.  Once in a blue moon, mid-grade ..and never premium, and I don't
want to discuss why not, btdt too much.

about the worse fuel economy for a waterboxer vanagon is in the winter, in
town, with a 2.1 and auto trans. Can be pretty seriously bad, even when
running perfectly.

scott
www.turbovans.com

----- Original Message -----
From: "PB" <pbrattan@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Wednesday, March 09, 2011 8:27 PM
Subject: STP Gas Treatment

> Nothing's wrong with my Westy, but would like to know if STP gas
> treatment will increase mileage and enhance performance.
> Patti
> 90 Westy Automatic