[V6-12v] High Mileage 100S

[James4ihl at aol.com]

That may be because your commute is so short. For a fair time of that commute 
your engine will be running on a rich mixture from the cold start which will 
gradually be leaning out. I first noticed how dramatic that effect can be when 
driving mum's car while mine was in shop. she has one of those brand new 
golfs with a spiffy little computer that tells you immediate and average/trip fuel 
consumption, etc. Well, it's a 1.8 Turbo engine and it's pretty economical 
unless you drive like Nikki Lauda, but when you get in and drive it from cold, 
the fuel economy for the first few minutes is frighteningly poor <17mpg for the 
first few minutes/miles, then it gradually leans out as the engine warms up. 
Consequently, if you flip the computer over to average mileage, on longer runs 
you'll get a very good average mpg, because for the majority of the run, the 
car has been in it's warmed up (leaner) fuel trim (about 38-40 mpg on 
motorways, for example). On shorter runs from cold, that average plummets 
dramatically, because the car's only been out of 'rich' warm up for maybe half the run, or 
less. Now if you think that that is a 1.8, with a turbo which helps increase 
fuel economy in the warm up phase by forcing hot exhaust gasses under pressure 
back into the combustion chamber, just think what your 2.8 non-turbo consumes 
in a longer warm up phase which is less efficient. If you look at it that 
way, it's easy to see why on a daily 15 mile run, you'd notice that you were 
getting a pretty crap average fuel consumption...

In a message dated 28/6/04 5:06:36 am, cdniederst at comcast.net writes:


> Geeze...I only have 113k on my '92 100S. My commute is <15 miles per day
> (that's total), so I don't chalk up the miles like you guys. In terms of gas
> mileage, I never see the numbers Jon is getting. I generally get ~18 mpg
> around the city, maybe ~23 mpg on the highway. I always run 93 octane gas,
> change the plugs at 30k intervals (with the OEM ones), changed the O2
> sensors at 75k, plus air and fuel filters every 15k, and never really see
> any difference. Car runs just fine, just wish I'd see the better gas
> mileage.
> 
> Craig