Hi all, I'm thinking of changing my '90 Acura legend over to a
synthetic oil product (Mobil 1 Amsoil..etc..suggestions?) and was
wondering what intervals I can expect between changes. One person I
was talking to said they can go to 25k. I don't know if I'd be
comfortable with that, though. The car currently has only 88K on it
now, but I put about 4k on it a month. Thanks for any input!
Why would you change the interval at all?
Synthetic oils won't break down as easily, it's true. But the viscosity
modifiers are the same as with conventional oils, and they will break down
just as quickly. Synthetic oils can't hold any more combustion byproducts
in suspension either, so if the limiting factor is the amount of junk in
the oil (as it is for most older engines), that's unchanged. In fact, the
better solvent properties of synthetic oils may cause them to get more
dissolved junk in them, when used on older engines.
"C'est un Nagra. C'est suisse, et tres, tres precis."
I somewhat disagree with Scott. The additive packages are rather
different on synthetics- for example most synthetics don't have ANY
viscosity modifiers to deteriorate. People who have done
long-drain-interval oil analysis on synthetics show that they do hold
their total base number (resistance to acid contamination) and wear
metal values just fine at long intervals, and the viscosity actually
INCREASES with age. But contamination and depletion of other additives
that are already being reduced for emissions reasons (zinc, for example)
are good reasons to not go much beyond a 7000 mile drain interval.
The Mobil 1 website, for example, strikes me as being careful to say
that if your car is under warranty you should follow the advice of the
owner's manual or (where fitted) the oil change idiot light, but that
their oils rated for various drain intervals will hold up their end of
the bargain if your car allows those intervals.
The push toward longer intervals seems mostly European in origin, and
is enabled by the fact that (by and large) modern engines in good
condition run cleaner than old ones. Yours, although old, is from the
era of modern closed-loop digital engine controls and if at 88k
shouldn't be running dirty if well kept thus far, but there are
things a newish car might get away with that maybe you can't. (What
do your smog-check numbers look like? And what is the rate at which
your engine consumes oil?)
This brings us to the question of how your particular example of your
engine, subjected to your driving cycle, dirties its oil, and with
Some airplane people (and expensive/high-performance car people)
incorporate occasional oil analysis into their maintenance observation
program, but ordinary drivers of ordinary cars do not find it at all
cost-effective, and where used, it is usually aimed at determining
when you're coming up on the need for an overhaul, rather than when
you need an oil change. I personally change it in the few to several
thousand mile range, depending on the car and the driving -- when it
starts to look or feel or smell dirty (yes, I sometimes get strange
looks, but my engines seem to last) erring on the side of more
There is no substitute for getting to know *your* machine...
PS. A quality filter is rather a lot of the battle against suspended
contaminants, though it won't do a thing about chemical contaminants
or particles below a certain size. I must confess to having done the
occasional drain'n'fill (especially on certain cars where the filter
was in a wicked location) but a premium filter (don't dismiss the idea
of getting OEM ones, especially if it makes sense for you to buy a
case at a time) changed with the oil is usually considered a good
Changing an 18 year old car over to synthetic? why? It's
a great car, but if you haven't used synthetic before now,
then what's the point.. If the engine has already been
subjected to "de rigeur' of a standard oil base for 88K
miles, then the damage that would have been prevented by
using synthetic, is already done.
If you want to keep the working parts in good shape, then
just use a good oil/filter and change it every month..
On Wed, 20 Aug 2008 11:21:26 -0700 (PDT), The Doctor
European cars often go 15 to 25K on synthetics and you might be able
to do so but it's a bigger stretch then I would be comfortable with. I
have switched all my vehicles over to Mobile 1 and a 12,000 mi or 12
month change interval. All of them had over 100K miles on them when I
made the switch. One developed a valve cover leak and I had to
replace the valve cover gasket. With modern engines there is no
reason to be changing more often then 6000 miles/6 months when using
regular oil and at least twice that on synthetic.
The podcast from WOR "The Car Doctor" has talked about this topic in
depth and breath over the past summer. You can either download the
podcasts from WOR or use iTunes to download most of the audio
The Car Doctor recommends a severe use schedule of every 3000 miles.
You have an older car but you will see a change in engine operation
should you decide to change to a synethic oil. However your extreme
use practically dictates you change the oil on a 3K interval.
There are those of the opinion that you should not change the type of
oil since the engine has been on the road for an extended period using
conventional motor oil. I disagree. If you like and have the budget
for a CarChip or any logging codereader, drive your car with
conventional oil for a week and then change to a synthetic oil.
The rwduced operating temperature of the oil and increased gas milage
should be ample evidence that the synoil works better.
Adam 96 Land Rover Discovery 1 in NYC USA
Mmmm. The original poster racks up an extreme amount of use, but is
that extreme use? In other words, is he delivering newspapers before
work and pizzas afterward, or slogging the length of a jammed urban
freeway to and from work; or just driving a long way on a fairly open
highway every day? Stop-and-go driving counts as dog miles, for
sure, but steady state highway cruise is a good scenario for trying an
extended drain interval.
Note also that if he *keeps* driving 4000 miles a month, that
odometer's going to turn over every other year. If the car is
presently in a well preserved state commensurate with its low mileage,
that would make me want to take care of it, including oil/filter
changes as frequent as needed, which again, may be the severe, normal,
or extended service interval. Those cars grow on people -- a good
friend had a '91 Integra and was very sad when the second time it got
stolen it didn't come back, aside from the financial reasons to keep a
good economical paid-for car going as long as it makes sense to do so.
PS. Changing the timing belt at the interval suggested by the owner's
manual is a good idea.
On Thu, 21 Aug 2008 23:41:41 -0700 (PDT), "Adam 1996 Cherokee Sport v6
Anyone can put on a radio show. Especially on weekends. Most stations
charge $50 to $250 an hour of airtime and you can say whatever you
want, sell whatever you want. Weekends typically are filled with
these paid shows that are little more then infomercial's. Having one
of these shows does not denote any special expertise. And if said
show is done by someone in the repair biz what do you suppose they are
going to say? Of course they want people to come back to their shop
every 3000 miles, it's another opportunity for a "50 point safety
inspection" where they can sell you fan belts, filters, tire
rotations, tire balance, rotate your muffler bearings, do an "injector
cleaning service", clean your brakes, adjust your bands, and on and on
with high profit margin, low cost "maintenance" done according to
THEIR, not the Manufacturers, maintenance schedule.
My '66 carubreted fume belcher does just fine on 7000 mile change
intervals using Shell RotellaT synthetic.
I'd worry a lot more about some modern under-designed dispose-a-car
econobox with an undersized oil filter, smallest possible oil pump for
lower parasitic loss, and undersized/overstressed bearings.
I change out the mobil 1 at ~7K. not so much that I don't trust the oil
or the engine running clean, but I don't trust that the filter does it's
job much longer than that. The V8 is clearly a strong engine, so that's
not an issue. I have thought about just replacing the filter and going
with longer drain intervals. But what's the point if I am going to under
there and get dirty to change the filter anyway? Might as well change
the oil too.
On the winter beater I used for a couple years I did do a filter only
change or two. But that car leaked enough oil that it was kind of
'self-changing'. At times I mixed the mobil 1 I drained from the '97
with some new walmart oil to top it off. Didn't do any harm.
Have you ever actually tried to figure out if the filter is anywhere
near capacity? In the past GM used to let filters go twice as long as
the oil (15,000 miles in the not so far past). I assume they had
reasons for doing so. And GM always specified tiny filters (by
comparison to Ford or Chrysler). I've cut numerous filters open, and
usually find nothing of note. The only time I found anything
disturbing was when I cut the SO's new RAV4 filter open at the first
oil change. There were some significant pieces of metal in that
filter, but after subsequent changes, I've found nothing. I always
change my filter when I change the oil, but I am not sure it makes any
sense to change the filter unless you change the oil. I've always
wanted to try and figure out how much "stuff" the filter collected,
but haven't come up with a good method yet. The empty filter weight is
easy to measure, but it is hard to measure the weight of a used filter
because they are difficult to fully drain, and because the oil soaked
filter media weighs more than the dry media. I've considered. filling
a new filter with oil and weighing that. Then, emptying and refilling
the same filter with clean oil when removed after use and weighing it
again. In theory this could give me a reasonable idea of how much
"stuff" the filter has collected. Of course what I really want to know
is the efficiency and flow capacity of the used filter. It is entirely
possible that a used filter is actually a more efficient filter than a
new filter, as long as it is not so contaminated that the bypass
No. I've just used rules of thumb of my own creation. The factory
recommended interval is 5000 miles, so I take that, add about 50%... and
that's the max I work with. For all I know it could last 14,000 miles
but I have no real way of measuring that. For a $3 part and a total
investment of ~$30 for the whole oil change, I play it safe.
Same here. If I had some way where I could *know* how the filter flowed
and what it filtered out after X miles I would trust it more. Instead
it's a 3 dollar part that was supposed to be changed every 5000 miles. I
figure there is a generous factor of safety involved, but is it 50%
more? 100%? 500%? No clue.
In my case I don't think Ford offers the 4.6L V8 or the FL820S filter in
europe. (not that some don't get there anyway)
That said, each model should be checked to make sure it really is the
same filter being used in europe. If it is, that would be sticking with
OEM filters. (wouldn't trust another brand not to have shot for the US
reccomended service interval) I would be comfortable with such a long
interval in that case.
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