On Sat, 8 Mar 2008 17:11:20 -0700, in sci.engr.mech "N:dlzc
D:aol T:com
\(dlzc\)" <dlzc1@cox.net> wrote:

Dear jim:

"jim" <"sjedgingN0sp"@m@mwt.net> wrote in message
news:1205019164_452@isp.n...
...
Doubtful the mileage drop is due to anything
intentional or that they did anything to "protect
the valves from running lean".

If you alter the mixture, by adding a litle more fuel,
the valves will run a tad cooler.

You keep saying this, yet you don't point to anything
they did to achieve this.

Just replacing the head doesn't do this. What was
the root cause of the lean running causing burnt
valves

and how was it changed?

To be honest given your posting history, this
almost appears to be a troll posting as you
given the lack of pertinent info.

Dear jim:

"jim" <"sjedgingN0sp"@m@mwt.net> wrote in message
news:1205019164_452@isp.n...
...
Doubtful the mileage drop is due to anything
intentional or that they did anything to "protect
the valves from running lean".

If you alter the mixture, by adding a litle more fuel, the valves
will run a tad cooler.

I would have someone check the timing belt.
More likely they did something unintentional - like
re-install the timing belt one tooth off.

OK. I have a list of things to check. (Including that they even
did replace the head with the valves.)

Thanks to all for the
suggestions.

David A. Smith

On Sat, 8 Mar 2008 17:11:20 -0700, in sci.engr.mech "N:dlzc D:aol T:com
\(dlzc\)" <dlzc1@cox.net> wrote:

Dear jim:
....
If you alter the mixture, by adding a litle more fuel, the valves
will run a tad cooler.

You keep saying this, yet you don't point to anything they did to achieve
this. Just replacing the head doesn't do this. What was the root cause of
the lean running causing burnt valves and how was it changed?

To be honest given your posting history, this almost appears to be a troll
posting as you given the lack of pertinent info.

"N:dlzc D:aol T:com (dlzc)" wrote:

Dear jim:

"jim" <"sjedgingN0sp"@m@mwt.net> wrote in message
news:1205019164_452@isp.n...
...
Doubtful the mileage drop is due to anything
intentional or that they did anything to "protect
the valves from running lean".

If you alter the mixture, by adding a litle more fuel,
the valves will run a tad cooler.

No not really. First of all there are 2 types of valves
(intake and exhaust) and without knowing any
specifics on which valves burnt or how, the notion
that a lean condition caused the valve problem
seems to be just wild speculation on your part.

Nor is there any evidence that correcting a valve
burning lean condition would reduce gas mileage.

If the engine had been running lean enough to burn
valves and they corrected whatever was causing that
lean condition then you should now be getting better
gas mileage.

I would have someone check the timing belt.
More likely they did something unintentional - like
re-install the timing belt one tooth off.

OK. I have a list of things to check. (Including that
they even did replace the head with the valves.)

If they said they did that - they probably did (what
motive would they have to lie).

However, your interpretation of why they did that may
be wrong. The fact that they replaced the entire head
suggests that there was some manufacturing defect
in the original head.

And then there is the question of whether any of this
means anything at all. You had a problem in the middle
of winter.

You check gas mileage as a consequence of the repairs -
you notice its down by 3mpg from the last time you
checked. Maybe the last time you checked was the
middle of summer. Maybe if you wait till July you will find
the mileage is back to 30mpg.

Mileage started decreasing. Mentioned to the dealership, they
spent more than the usual time, came back with "compression
low... not spark plugs, might be head gasket, valves, or piston
rings... we will let you know in a bit". Came back with "it is
valves".

The only way intake valves get burned is if they are left open
during combustion,

Nor is there any evidence that correcting a valve
burning lean condition would reduce gas mileage.

More fuel gets expended for each cycle of the piston, how could
it not affect mileage?

If the engine had been running lean enough to burn
valves and they corrected whatever was causing that
lean condition then you should now be getting better
gas mileage.


I respectfully disagree with the diagnosis, but do agree that I
*assumed* that the dealer "enriched" the mixture when they might
not have. They may simply have chosen the wrong cause for the
lack / loss of compression.

However, your interpretation of why they did that may
be wrong. The fact that they replaced the entire head
suggests that there was some manufacturing defect
in the original head.

Perhaps. But they did identify failed / failing valves.

And then there is the question of whether any of this
means anything at all. You had a problem in the middle
of winter.

Late summer. Still 100+ degF in the daytime.

You check gas mileage as a consequence of the repairs -
you notice its down by 3mpg from the last time you
checked. Maybe the last time you checked was the
middle of summer. Maybe if you wait till July you will find
the mileage is back to 30mpg.

Mileage has steadily declined through the "winter", and now that
it is back up to 80 degF, the mileage is not increasing. I get
an instantaneous and long term trend on mileage (via computer),
and have confirmed that it is a good indicator with the miles
travelled between fillups. I checked it when I first got the
car, and again when the dealer said "oh, you cannot trust it"...
with this last observation to them.

There had never been more than a 1mpg variation summer-to-winter
prior to this "incident". I steadfastly refuse to run A/C, even
when it is 110+ degF in the summer, since my house is never as
cool as my car... mkaes it even nicer to be home.

Thanks for your persistence. Lets hold off for two weeks, and
see what the diagnosis is.

David A. Smith

Dear me:
me@mine.net> wrote in message
news:2ec6t3ho9rmcm0pl265s86esdijohavnmv@4ax.com...

You keep saying this, yet you don't point to anything
they did to achieve this.

Can you adjust injector duration to be slightly longer, in
response to a given air flow?

Just replacing the head doesn't do this. What was
the root cause of the lean running causing burnt
valves

I would say "marketing and/or legal pressure" to get higher gas
mileage out the door... regardless of what it might do to the
lifespan of the engine.

and how was it changed?

Software, perhaps.

To be honest given your posting history, this
almost appears to be a troll posting as you
given the lack of pertinent info.

Think what you like. I don't work on engines anymore. This
allows others some employment, and I hate getting black crap
under my fingernails "daily". I have this one new car, and four
used ones...

I found a small reduction in mileage reasonable, to keep the
valves from burning out again. I was hoping for some informed
opinions as to whether almost "20% loss of mileage" was
reasonable, or where I should direct the mechanics to look for
the next / real problem.

I got some suggestions (timing, valve timing, failed piston
rings, probably therefore failed ECV, munged oxygen sensor), and
I have thanked those that offered suggestions.

As to trolling...
http://groups.google.com/groups/search?q=dlzc&qt_s=Search+Groups
32,200 hits, dating back to 2000, and I have tried to be helpful
in every post. Sometimes someone twists my titties, or steps
into my space and accuses me of things, and I forget that we were
all born ignorant, naked, wrinked, toothless, and ugly.

How's the oil?

Do you smell gas in it from a lot of blow-by indicating
the rings or worse are shot?

I have a 2004 Chevy Cobalt (aka. Cavalier). When new, I was
getting 30.5 mpg or so. Then about 45,000 miles the valves
started to burn. Replaced the heads under warranty, and the
mileage has dropped to about 25.5 mpg... with the same lead foot
in the same kind of traffic.

I understand that running lean will make the valves hotter.

But this thing has no guts (not that it had much before), and I
really miss the extra mileage.

The dealership says that it is set for factory settings...

Ideas?

David A. Smith

Thanks for your persistence.  Lets hold off for two
weeks, and see what the diagnosis is.