[Vwdiesel] fuel consumption during idle?CCCcccold here !

[Val Christian]

I'd argue it's academic.

Assuming the problem is compression related, there is enough blowby
so that the oil is getting pretty sooty at cruise.  Idle will be 
less dirt, but more time.  First order, we can assume that the soot
is linear with the throttle.  It's probably really that the soot is
something like the square of the fuel.

Since the oil is getting dirty,and there are problems starting, the oil
will get changed frequently.  (Cheap $0.99/qt stuff is fine at frequent
intervals.) 

Oh, when the oil gets sooty, and if it's thick, then it tends to help 
rings stick, which makes the problem get worse faster, with more blow-by.
Another reason for real light oil for the dead of winter.

Let's be clear here, and I am making some assumptions, when you have a 
high time engine, which is in less than ideal shape, you want to 
milk the max utility out of it, without an unreasonable compromise in
reliability and safety.  If it's an aircraft engine, you don't want it
to fail in flight.   If it's a VW diesel, you want it to start.

I haven't had a VW diesel that won't start in -25C or -35C if it's in 
good shape.  When they start getting "fair" then the cold start may be 
compromised.  The cause could be compression, injection, timing, valves 
or whatever.  There are reasons to prep your car in the fall, before the
cold WX begins.  

But once you're there, the objective is to keep it running and get you 
from one point to another.  If on the coldest day, you need to keep it
running from 10 to noon and 2 to 4, so that you can go home, so be it.
Over the years, usuallydriving the high miler in the household, I've
just gotten in the habit of carrying two keys.  Start the car, run the
heat on low, and lock it.  When I've been on trips and it's -35C outsde,
I've done just that while grabbing a meal or something like that.

When I'm at home, I can use propane, preheat the oil, heat the cylinder
head, pour in warm fuel, whatever.  It's not an option at work.  Fortunately,
no one really notices it when I'm away for 10 minutes, so there have been
cars where I've idled it for a while, usually starting the car around 
2PM, while the day is still "warm".  It's inconvenient, but the rest of
the year, the car runs OK, and costs allot less than the alternatives.

Besides, diesels always start on hot days, and the same cannot always
be said of fuel injected gassers.

So there a balance between keeping it running most of the time, and 
going overboard of trying to keep it going.  Expensive coolant heaters,
fuel processors, etc. need to be traded against reringing or a engine 
overhaul.  I even had one Rabbit which always had a "slow" starter.
When it got old, and cold, it wouldn't start.  I just happened to 
swap the started out of it one day, and my cold WX start problems 
went away for a few more years.

The beauty of DIY is that you get to know your vehicle.  The more you
know, the more it can make it work for you.  And you can make the 
compromises on what to fix preemptively (scheduled maintenance), 
what to fix when it shows symptoms (demand maintenance) and what to 
not fix (non-maintenance?).  Presumably you make these choices
for economic benefit, self-satisfaction, or some other metric.
But as a DIYer, you get to choose.  (State inspections not withstanding.)

I'll stop here, because I'm probably not helping anyone do an actual repair.

Val







> 
> Diesels consume VERY little fuel at idle.  No pumping losses to=20
> speak of, and it doesn't take very much power to just spin a crankshaft.
> BUT, and it's a big BUT, you will not be doing any favors to your oil
> by running the engine that cool for a long time. =20
> 
> > -----Original Message-----
> > From: Mark Shepherd [mailto:mark at shepher.fsnet.co.uk]
> > Sent: Friday, January 28, 2005 12:44 PM
> > To: vwdiesel at vwfans.com
> > Subject: [Vwdiesel] fuel consumption during idle?CCCcccold here !
> >=20
> >=20
> > Mike just pull the fuel supply and return and dunk them in a
> > measured jug of fuel run for 1/2 hr and you'll know..Just
> > let level settle for a few minutes first..
> > Miser
> >=20
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> >=20
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