Denial is running strong. You just aren’t that sensitive to notice a 2% change in power and if you can't get to 70-75 on level road you have a problem. It is possible to have something wrong that is not internal to the engine. Do or get some diagnostics done and figure it out. One possibility is the catalyst failed and is plugging up the exhaust. Compression and leak down test will confirm engine condition. Could even be power loss due to a sensor or injector issue such as a bad O2 sensor system. 

Dennis

-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of Michael Hart
Sent: Tuesday, November 10, 2015 4:32 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Power & MPG Summer/Winter

Over the past ~3 weeks I've noticed a slight drop in power & mpg for my Westy (what power you may ask?). Specifically it feels like i'm fighting a headwind on the freeway at 50 - 60 mph.
Searching for answers and hoping it is not a real engine problem (this 2WD Westy has 195k on the original engine), I followed a hunch on gasoline formulations & found the following;
- the winter gasoline formulation for California has an average of 1.7% lower energy content (vs. summer) - due to added butane
- the changeover date is Oct 31st (most stations switch over a little
earlier)
- other factors that affect fuel economy include air temperature (the daytime temperatures have dropped significantly over the past two weeks
here)

http://www.afdc.energy.gov/pdfs/2876.pdf

Having read all this I am less worried that the engine is on it's last legs (I still have no really good excuse to spend large $$ on a new engine...)
--
Mike Hart
Palo Alto, CA (SF Bay Area)
1987 2WD White Westfalia GL 'T3Westy'