From: cbm@athena.mit.edu (Charles Bruce Musgrave)
Newsgroups: rec.autos.driving,rec.autos.tech,rec.autos.misc,rec.autos.vw,
	rec.autos.sport.tech
Subject: Re: ###Sythetic vs. Petro Oil, some common sense,PLS###
Date: 29 Jun 1995 12:50:08 GMT

In article <3ssmvo$jv2@elaine25.Stanford.EDU>, olee@leland.Stanford.EDU
(owen gee hong lee) writes:

|> This has been a hot subject and I have seen many posts on the net.
|> But come on and let's use some common sense.  From all the verifiable
|> information that I've seen, synthetic motor oil is not cost effective.

Are you saying if you use it as 100 percent synth or mix it (what most 
people should do)? Or are you saying if you don't increase the drain interval.


|> Let's use some common sense:

Next time I need to solve a chemical molecular interaction problem I'll
just use common sense rather than firing up any simulations tools and 
wasting all that silicon CPU ;)


|> 1)  burning gas produces water, part of the water produced will invade
|>     the motor oil.  Even if synthetics can neutralized the effect of
|>     damagin acid, motor oil should be changed to get rid of the moisture
|>     buildup.  There are things that an oil filter can not trap that will
|>     increase wear if the oil (even if it's synthetic) is not changed
|>     regularly.

Of course combustion produces water, but at operating temps it gets vaporized
just like most of the other combustion by products. Some byproducts can 
aggregate and form sludge, etc (if the car does not reach a high enough temp
for long enough) which can be abrasive and which can no longer be vaporized.
Water however won't do this, nor is it nearly as bad for most engine materials
as dirt, and the various acids formed in your engine. Synth has a higher 
particulate loading capacity for abrasive and acidic species, but water is
not a problem for either oil.


|> 2)  The thermostat controls engine temperature.  If synthetic oil is used,
|>     and IF it reduces the amount of heat (big IF), the cooling system of the
|>     car will simply take less heat out to maintain the operating temperature
|>     Your engine running temperature will not be reduced by using synthetic
|>     oil.

So your water pump will operate less and the overall average temperature will
be lower (the temp at the coolant channels constant, but the temp at the 
cylinderwalls lower (Diriclet boundary value problem). This isn't much of
an effect anyway since friction is not the largest heat producer nor is
lower oper. temps the reason for using synths. 


|> 3)  Sythetic motor oil does not reduce fuel consumption.  No verifiable
|>     study has been done to prove that synthetic oil increases gas mileage.
|>     This is a claim only, mostly from synthetic oil sale people.

There is quite a literature on the reduced friction given by synthetics.
Much of the work was done for gear oils in industrial machines, but many of
the same lubrication/tribological issues were the same. Common sense would
tell you that you are going to get a different gas mileage...it has different
properties, flows differently, etc. and has a different internal friction
coefficient. Corn oil is oil too...think you would get the same gas mileage
from corn oil?


|> Synthetic lube products are better than petro oil in two regards:
|> 
|> 1)	higher threshold temperature for catastrophic breakdown.
|> 	But no engine with a functional cooling system will operate near
|> 	the temperature for catastrophic breakdown of petro oil, even at
|> 	peak engine output.  Synthetic is offering a safety margine that


No. Breakdown is governed by kinetic reaction rate theory. There will 
be breakdown at operating temps, but it will take some time proportional
to the Boltzman probability for the reaction. Your engine oil will breakdown,
it is only a mater of the rate of breakdown (which of course is higher with
higher temps, but not zero at oper. T as I mentioned).

|> 	you will never need.  if your engine colling system dies and you
|> 	keep running, you will exceed the temperature for catastrophic
|> 	breakdown of synthetics anyway.

Depends how long you drive after you lose your coolant.


|> 2)	Less viscosity breakdown at normal operation.  But if you measure
|> 	viscosity of a synthetic as then end of 10k vs viscosity of a petro
|> 	oil at 5k, you will most likely find that the petro oil has a better
|> 	viscosity.

Not from the data I have seen. The synth maintains more of its viscosity, which
is generally lower to start with and continues to have a flatter V vs T curve.


|> Think about it, if any of the claim (reduce fuel consumption, reduced
|> engine temperature, etc) can be proven by a scientific study, wouldn't
|> the oil company have paid the money for the study and shout the result
|> out to the world (just

They have been proven. I think you need to look at the literature. Anyway, 
these are not the main reasons for using a synth. Higher particulate loading
is, better cold start lub, etc. etc. The research I've seen was sponsored 
by tool manufacturers. Go look it up.

|> like slick50 had done)???  Synthetic oil serves a niche market right now,
|> and it's very profitable (most niche markets are) because people are paying
|> a high premium for it.  Growing that market means LOTs of money for the

Good thing you can get most of the synth properties by mixing it with mineral
oil 1:4 or 1:3 say and greatly reduce the cost.

|> synthetic makers. Why are they not doing it with scientific studies (or
|> even pseudo-scientific studies for those who are scrupulous) and
|> national campaigns advertising the results of those studies.
|> 
|> BECAUSE they know they can't prove it!!!!!
|> Flames welcome, but pls no personal attacks.

Hum. I am a scientist who has worked in tribology and am not funded or
working with any of the synth makers. I have read much of the research.
Read the abstracts if that is all the time you have. Key words Synthetic, 
lubrication, ester, engine, wear, etc.

Charles

From: dheister@magnus.acs.ohio-state.edu (David J Heisterberg)
Newsgroups: rec.autos.driving,rec.autos.tech,rec.autos.misc,rec.autos.vw,
	rec.autos.sport.tech
Subject: Re: ###Sythetic vs. Petro Oil, some common sense,PLS###
Date: 29 Jun 1995 15:34:30 GMT

In article <3ssmvo$jv2@elaine25.Stanford.EDU>,
owen gee hong lee <olee@leland.Stanford.EDU> wrote:
>1)  burning gas produces water, part of the water produced will invade
>    the motor oil.  Even if synthetics can neutralized the effect of

At operating temperature you'll boil off much of the water.

>    damagin acid, motor oil should be changed to get rid of the moisture
>    buildup.  There are things that an oil filter can not trap that will
>    increase wear if the oil (even if it's synthetic) is not changed
>    regularly.

Blow-by is the big culprit in motor oil degradation.  I was somewhat
surprised to find that blow-by is roughly

  80% fuel/air
  20% combustion products
  up to several hundred ppm of NOx

The NOx oxidizes the base oil, forming varnish and sludge.  Anti-oxidants
are added to help prevent this.  Yes, this does occur with synthetic as
well as mineral oil, but synthetics are more resistant to NOx attack and
with a higher film strength, can reduce blow-by.

>2)  The thermostat controls engine temperature.  If synthetic oil is used,
>    and IF it reduces the amount of heat (big IF), the cooling system of the

I still don't believe this claim.  Steady state temperature is above the
temperature at which the thermostat opens.  The thermostat does not
control steady state operating temperature.  That's my theory and I'm
sticking to it, but if someone who really knows would like to correct
that, please do so.

>Think about it, if any of the claim (reduce fuel consumption, reduced
>engine temperature, etc) can be proven by a scientific study, wouldn't
>the oil company have paid the money for the study and shout the result
>out to the world (just

I agree that you would be hard-pressed to find a significant decrease in
fuel consumption with synthetic over a good mineral oil.  As to reduced
engine temperature that's not very well defined: coolant temperature
coming off the heads doesn't tell you what's going on at the rings.  And
anyway, reducing temperature is not an end in itself.  What synthetic
oils are really aimed at is reducing wear, especially in high load, high
rpm operation.  This is verified and the manufacturers do shout about it!

Synthetic oils are expensive, but if I had, a $30,000 ZR-1 engine I'd
use them.  Or even if I had a $5000 spec racer engine that ran at 7000
rpm for 20 minutes at a time.  As it is, a quart of Mobil-1 5W30 is a
pretty cheap way of improving dead-of-winter operation.
-- 
David J. Heisterberg                        Ich grolle nichte, und
Dept. of Chemistry OSU /                  wenn das Herz auch bricht.
The Ohio Supercomputer Center               -- Heine

From: cbm@athena.mit.edu (Charles Bruce Musgrave)
Newsgroups: rec.autos.tech
Subject: Re: Synth oil bad in the winter?
Date: 29 Aug 1995 21:24:01 GMT

In article <41va0p$7ee@bronze.lcs.mit.edu>, adam@bronze.lcs.mit.edu (Adam
Glass) writes:

|> Jerry <gmc@mlb.semi.harris.com> wrote:
|> > The reason synthetics can perform over extended drain intervals is
|> > precisely because they are cleaner, they form deposits at much
|> > lower levels. Combine this with uniform size molecules that roll
|> > better, and are more slippery, and with greater tolerance for
|> > wider temperatures, and it seems to be a no-brainer what to use.
|> 
|> I'm currently using Mobil 1 in my car, but I've been wondering about
|> this for a while.  I've read all of the FAQ's, testimonials, and web
|> pages I've been able to get my hands on.  I've listened to the various
|> arguments here, on rec.auto.sport.tech (good grief), and from the
|> various oil companies, and I'm still not sure.
|> 
|> Here are my specific questions and concerns:
|> 
|> 1) Yes, it seems that synthetics are superior lubricants and have better
|> wear properties.  But has anyone doing regular 3000 mile drain intervals
|> with a conventional oil experienced a *lubrication-related* failure?  So
|> what if the synthetics lubricate better, if the conventional oils
|> are sufficient (provided they're changed every 3k miles.)

3000 is such a conservative change frequency that those failures are few
and far between. Under normal conditions the protection in the conventional
oil at 3000 miles is still quite good. The synth will stay that good until
somewhere in the 10,000 mile range. If you drive in any kind of adverse
conditions, the synth wins out. Drive on a dirt road? Extreme cold starts?
Lots of short trips around town? Synth better in these conditions by far.


|> 2) Don't *all* oils get contaminated to some degree by various
|> external pollutants that make it into the oil?  (Acid from combustion,
|> etc.)  Or does this only occur in appreciable amounts in cars with

Yes. Synth has a higher particulate loading capacity so it can handle 
the contamination better. It also resists acid/oxygenation reactions. 

|> worn rings?  If it happens in all cars (to some degree), you'd want

It is most likely to get in through your valves, not worn rings.

|> to have short drain intervals anyway, in which case synthetics lose
|> their claim of being able to extend drain intervals.

Then why not just put 1950s technology oil in your car? All oils have
additives to improve their properties. Synths just go further in 
achieving those properties over a longer drain interval.


|> Although I'm currently using one, I remain skeptical that synthetic
|> oils are worth the extra expense.

Don't use a pure synth. Use a mix with conventional. 1:3 works
well and is a lot cheaper.

|> 
|> Adam

Charles

From: John De Armond
Subject: Re: Synthetic Oil in remanufactured engine
Date: Fri, 01 Oct 1999 14:30:55 EDT
Newsgroups: rec.outdoors.rv-travel

Ajbate wrote:
> 
> Perhaps Corvettes do something to the engine, like run it before being
> released? I don't know why they can run synthetic oil from the factory. I do
> know that a few years ago I put some of the new vans in my fleet on synthetic
> oil as soon as I got them and the rings did not seat. I drained out the
> synthetic oil from some of them and put in regular oil. Within about 2,000
> miles the ones with regular oil seated, and the others that still had the
> synthetic oil still were not seated!  I don't know what Corvettes do at the
> factory.

The difference is modern manufacturing practices and tolerances.  I
don't have the Corvette spec but the spec for GM's 4 cylinder
engines for cylinder taper and roundness is about 0.00005" and the
surface finish spec is essentially that of a broken-in engine of
even 5 years ago.  In other words, modern engines are manufactured
to be "broken in" as delivered.  That is why there is no longer any
extended breakin procedure cited in the owner's manual.  Modern CNC
machinery and the requirement to warranty the engine to meet
emission specs for 100k miles are the driving factors, with the cost
of consumer protection laws being right behind.

Summary:

New engines - Synthetic is probably OK.  Follow the owner's manual
recommendation.

Rebuilt engines - No synthetic until broken in.

John

From: John De Armond
Subject: Re: Synthetic Oil in remanufactured engine
Date: Fri, 01 Oct 1999 21:16:19 EDT
Newsgroups: rec.outdoors.rv-travel

will@epix.net wrote:
> 
> The anonymous & obnoxious <info@panva.com> writes:
> 
> > Once again Will's 1950's technology shines through...Hey Will, it's
> > 1999 and you don't know what the hell you're talking about!
> 
> Since there is no quotation, we must assume this outraged whimper is
> from a regular heckler who thinks (assuming he/she/it has enough grey
> matter) 1999 synthetic oils *eliminate* wear to the point that "rings
> don't ever seat".  News from the front, Bozo: wear has yet to be
> *eliminated* by lubricants.  The finest may indeed REDUCE wear rates,
> operate well under a wider range of temperatures than oils from the
> '50's, and make your Mobil stock rise.  But they are NOT so good that
> they prevent all wear.

At the risk of getting into a Clinton-style pubescent pissing
contest over the definition of "eliminate", perhaps I can add some
substance to this discussion.

First off, I built racing Datsun Z engines for over 15 years and
continue to do restoration work on them.  I also consult on matters
relating to engine management, dynamometers and data acquisition
systems with some of the major engine building operations in this
country.

Neither I nor any engine builder I know recommends using synthetic
oil during the break-end period because synthetic oil effectively
eliminates the wear necessary to seat the rings in a cylinder
finished to typical aftermarket specifications.  This is based on
fact born of experience.  This issue has been settled for years.

Secondly, the owners manual in my wife's Camry specifically
recommends against synthetic oil before the first recommended oil
change.

Thirdly, Toyota, responding to a question from the Toyota MR2
Owners' Club about the use of synthetic oil, had this to say:
--
We  recommend that synthetic
oil not be used during the "break-in" period of an engine.  The
reason
for this is that synthetics, possessing extraordinary lubricity and
lubricant film strength, do not permit the metal wear necessary for
the
seating of piston rings.  A change to synthetic motor oil should
wait
until you new or rebuilt engine has completed the break-in period of
six
to eight thousand miles.
--

Synthetic oil usage for NEW Current Production engines may or may
not be an issue - I don't deal with new vehicles anymore.  I suspect
that it is much less of an issue because of the surface finish
applied to cylinder walls using modern CNC machinery.  In any event,
my advice would be to follow the manufacturer's instructions in the
owner's manual.  After all, what the hell do they know?  They just
designed and built the engine.

My recommendation to a customer who buys one of my engines is to run
the engine on regular 10W30 until the oil consumption has stabilized
and only then convert to synthetic.  Even then, expect the oil
consumption to increase on synthetic.  Don't know why, it just
does.  Probably because of the lack of long chain index enhancer
additives necessary for refinery-based oil.

As to your reference to "50's oil", Will, about the only thing oil
from that era and now have in common is that they come from the
ground.  Mostly.  Perhaps if you'd like to have some actual
information with which to argue, you might go to http://www.sae.org,
go to their online store and buy yourself a copy of the transactions
of any of the recent lubrication symposia.  It'll cost you a C-note
but who knows, you might learn something.

John

From: John De Armond
Subject: Re: mobil 1
Date: Sat, 13 Nov 1999 03:06:19 EST
Newsgroups: rec.outdoors.rv-travel

Hugh Darling wrote:
> 
> Hi Dick, I went to the Mobil home page and found nothing to
> support the post (dont have it now) that said Mobil 1 could
> be put in from mile 0. Your post agrees with my
> understanding of use of synthetic oil.

Hugh,

As you noted, Mobil recommends NOT using Mobil 1 in a new engine. 
Since Mobil has no idea what kind of engine the reader might put the
engine in, the advice has to be generic.

Modern manufacturing machinery and techniques result in
unprecedented surface finish and tolerances. The Corvette's engine
has its pistons set up with less than 0.001" clearance, compared to
the more typical 2-5 thou.  The allowable wall taper and
eccentricity is expressed in microinches. The finish on the machined
surfaces right off of the machining centers is better than older
engines after breakin.  The Corvette engine can use Mobil 1 from the
beginning because it was designed and manufactured that way.  Other
less premium engines might not be.  I have confidence in the
japanese engines and the high end of US engines.  But, say, a
Hyundai or a Geo Metro?  I'd not risk it.  Ditto on generator
engines. Ditto reman'd engines.

There is literally nothing to be gained by putting synthetic oil in
an engine too early.  There is a lot to lose.  The establishment of
wear patterns is essentially stopped when the synthetic goes in.  If
the engine is still burning oil because the rings have not seated,
they will remain that way.  Why push it?

John

From: John De Armond
Subject: Re: mobil 1
Date: Sat, 13 Nov 1999 16:43:00 EST
Newsgroups: rec.outdoors.rv-travel

AJKing554 wrote:
> 
> On 11/13/99 >Neon John johngdNOSPAM@bellsouth.net writes concerning the use of
> synthetic oil:
> 
> >There is literally nothing to be gained by putting synthetic oil in
> >an engine too early.  There is a lot to lose
> 
> Correction, there is a little to be gained and NOTHING to lose.
> 
> > The establishment of
> >wear patterns is essentially stopped when the synthetic goes in.
> 
> Why, oh why, does this old wive's tale about synthetic oil refuse to die?
> Synthetic oils use the same types of additive packages that standard oils use.

In my case, Three reasons.  a) That's what Mobil officially tells
the public, b) That's what my engineering contact at Mobil tells me
and b) that's what my oh, 30+ years of building and operating racing
engines tells me.

I use synthetic oil in racing engines (actually I've found Honda's
house brand to work better than any of the rest) but I do NOT use it
in my street vehicles.  The marginal added benefit is far outweighed
by the additional cost and the added consumption.  I fire a new
engine on conventional oil because I KNOW that with aftermarket
machining practices, the relatively rough finishes and loose
tolerances will not bed properly on synthetic oil.  A high
preformance oil burner is much more serious than a street vehicle
because oil in the chamber causes knock which will quickly destroy a
racing engine.  Once I have a couple of hours on the engine,
preferably on the dyno where I can control conditions, then in goes
the synthetic.

I know this is heretical to the True Believers in the Magic of Motor
Oils but I have the experience and the evidence to prove that for a
street engine, the type oil doesn't really matter much as long as it
meets the proper cert.  I'm a fan of old cars.  I get very attached
to my cars.  I almost never sell a car.  The newest vehicle in my
fleet is my 82 MH.  Among them are the following:

68 Fury, 318 V8 - 270,000 miles.  Bought with 40k miles on it. 
Engine changed for a higher performance engine at 240,000.  Old
engine used about a quart of oil to a tank of gas, mostly leakage
past the rear main.

75 Datsun 280Z - 360,000 miles.  Bought new.  Engine changed at
320,000 for a high performance one.  Fairly tired but oil
consumption still below a quart per 1500 miles.

70 Ford F-250 Camper Special pickup - 150,000 miles.  This truck has
a very low rear end so the engine turns many more revolutions per
mile than the above vehicles.  Engine just changed out because of a
cracked head.  Used about a quart of oil per tank of gas.

1975 Chevy 14' Step Van.  - Est 380k miles.  Chevy 350 that operates
wide open most of the time.  Targetmaster engine installed about 80k
miles ago to replace the thoroughly worn out engine.  This van came
out of the federal fleet from an agency whose policy is "no oil
change".  Van is used almost exclusively for local delivery

1980 BMW 635CSi - 120k miles.  Bought practically new.  No oil
consumption.

Oh, and my wife's 89 Camry - 200k miles.  Zero oil consumption.

And so on.

My policy is to buy the cheapest brand name oil on the shelf
(usually Wal-Mart's house brand) and to change the oil and filter
every 10k miles.  The results from testing the oil from my vehicles
indicates I could go longer but I like 10k since it makes it easy to
remember when to do it.  When the odometer turns all zeros on the
right, time to change oil.

The one key thing I do is to never operate the engine so that the
oil remains cold.  If a short trip is necessary, it either waits for
other missions to accumulate or else I take a long, leisurely trip
around our bypass.  Either way, the oil is fully warmed before
parking.  That and keeping the maximum oil temperature below about
280 degrees are the two thing any oil engineer will tell you is the
key to long engine life.  If you really care enough to argue about
these things, invest $30 in an oil temperature indicator.
 
> There are two conditions where the use of synthetic oil will significantly
> reduce wear relative to standard oils:
> 
> 1.  Operation with engine oil temperature consistently above 300 degrees
> fahrenheit.  The higher level of refinement present in synthetics allows
> retainment of  proper lubrication to about 320 degrees.

You know that from testing or is this regurgitated oil company
propaganda?  I suppose synthetic oil will bail you out to a degree
when you're running under abusive conditions but the real solution
is to not let the oil run that hot.  An oil cooler costs little more
than a couple of synthetic oil changes, after all.  Assuming that is
a concern, you DO have an oil temperature indicator, don't you?

> 2.  Cold starts below -20 degrees fahrenheit.  The pumpability coefficient of
> standard oils starts to drop dramatically around this temperature (assuming
> same weight oils) compared to synthetics.  Again, this is due to the higher
> refinement levels of the base oil in synthetics, not to some magic in the oil's
> formulation.

Well, where I live, if my vehicle every sees 20 below, it will be
because I somehow drove it into my walk-in freezer!  Most of the
normal engine wear occurs before the pressure comes up regardless of
the cold viscosity.  If you really want to affect cold engine start
wear, install one of the fairly inexpensive preoilers and build oil
pressure before you turn over the engine.  A pre/post oiler was a
vital ingredient in my Datsun high performance turbocharger
installations.  I could count returns for turbo failure on one hand
and have fingers left over, in stark contrast to some of my
competitors who used just about the same components but left out the
oiler.

Ultimately we all do what we're comfortable with.  If synthetic oil
in a street engine makes you comfortable, where that's what it is
there for.  For me, regular oil has worked just fine.

John

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Regular oil vrs. synthetic oil
Message-ID: <8ndnjvo30e5te937fmpb2rqh5drtqj95b0@4ax.com>
Date: Thu, 14 Aug 2003 12:27:10 -0400

On Wed, 13 Aug 2003 14:24:08 GMT, MTV <NoSpam.mvolz@houston.rr.com> wrote:

>maxandkitty wrote:
>
>> I was looking at different oils at wall-mart the other day and was wondering
>> what the difference was between the $3.50 synthetic oil and the $1.50
>> regular oil.  Does the synthetic withstand more heat and doesn't have to be
>> changed as often?  Also synthetic trans. fluid, is it worth the extra $$$$?
>>
>Yes. Yes. Yes.
>My gas mileage also improved with Mobil 1. I also switched to GM
>synthetic ATF & rear axle lube.

I've become a real fan of Mobil 1.  I've always used synthetics in my air
cooled and racing engines.  My current car convinced me of the value of the
stuff in a normal engine.  It's a 94 Caprice 9C1 police special with the
'Vette type engine.  It was a chief's car and had been very well taken care
of.  GM recommends Mobil 1 for the LT1 engine and that's what it came with
from the factory.  I got the fleet records with the car.  they did routine oil
testing and changes every 25k miles.  Now with 100k miles the engine uses not
a drop of oil.  Inside the valve cover the parts look like brand new parts,
not even darkened.  This engine is still practically as tight as when new.
This is particularly impressive given the abuse and idling a cop car
experiences.

The extended change interval more than makes up for the cost difference.  My
only caution is to wait until a new engine is broken in before changing.
Mobil 1's lubrication is so good that it can prevent ring seating, resulting
in continuous low oil consumption.  I know that Mobil now says this isn't
necessary but based on experience, I'd rather be caution.  I use dino oil for
the first 500 miles or so and then change.

John

From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Regular oil vrs. synthetic oil
Message-ID: <fvjojvobqt0ep61hp347vk90snue8i54q2@4ax.com>
Date: Thu, 14 Aug 2003 23:19:59 -0400

On Thu, 14 Aug 2003 09:43:17 -0700, Alan Balmer <albalmer@att.net> wrote:

>On Thu, 14 Aug 2003 12:27:10 -0400, Neon John
><johngdDONTYOUDARE@bellsouth.net> wrote:
>
>>The extended change interval more than makes up for the cost difference.
>
>How do you determine the change interval? Analysis?

I guess that if you want to be anal... :-)  In the case of my car, I have the
service records and so a history.  The oil tests never indicated anything
wrong and I believe 25k miles is Mobil's recommended max.  Since my driving
puts less stress on the system than cop duty I am comfortable adhering to
their schedule.

I have almost 20k on the oil right now and it still looks as clean as fresh
dino oil.  Just the tiniest bit off-color.  Out of curiosity I might send a
sample off for testing at the 25k mark.  I bet it will still be satisfactory.

I'm going to put Mobil 1 in the new engine for my MH when I install it (after
break in, of course.)  I'll probably test once or twice to set the change
interval but I anticipate 25k miles.  At just a touch over 7000 lbs the rig
presents about the same load to the engine as a full sized Suburban - IOW, not
that much.

John