[Vwdiesel] 1985 1.6TD Jetta recently acquired

Val Christian val at mongobird.com
Wed Nov 29 12:47:07 EST 2006

While it is true that extended drain intervals on non "C" rated
oil could impact compression, and other engine functions (bearings, etc.),
any damage from using a non-"C" rated oil would most likely be
overshadowed by the hours on the engine, and the way it was 
operated and maintained.

I can say this from the experience of running well over a million, or
perhaps two million, miles on VW diesels, using non-"C" rated oil.
In the early 80's the "C" rating and the "S" rating became almost 
mustually exclusive.  Until that time, I generally used Castrol 
products.  Subsequent to that time, I used a variety of "S" rated 
oils, usually branded as Mobil or Shell, and sometimes "store brand".

Many here will be tired of hearing the story, but in 05, my daughter 
replaced a leaking cylinder head gasket on a 91 Jetta which was 
bought new.  That engine has seen much more "S" rated oil than "C"
rated oil over it's life.  The compression was 495 +/- 5 in all cylinders
prior to the teardown, and the cylinder wear was well within spec,
even though the engine had 200K miles on it at the time.

Generally speaking, that car has had oil changes every 3000 miles, however
the mean time to change oil has been a little over 4000 miles.  This is
because of personal schedule, or perhaps I was running a "C" rated oil
at one time or another.

Again, it is true that a "C" rated oil can better handle soot and free
carbon, however, it is limited in it's ability to do so.  I believe that 
for similar grade oils, the soot retention capability is less than a 2X
differential with "S" oils.  (My tribiologist is not available.)

So frequent changes, even with a low cost "S" oil, does work, and it can
be cost effective.

Let me address your compression issue.  If you are having a problem
which could be compression caused, then check the compression.  Harbor
Freight has diesel compression gauges for less than $30.  I don't 
have experience with their tool, but the one I use cost less than $100.

If you have the injectors out, or if you're going to pull the head, then
check the compression, to get an idea of the condition of the engine.
If you simply want to get a metric on how the compression is doing, wait 
until you have a few hours ~25 on the engine, so that you get a realistic 
reading of the general condition.

Should you end up pulling a head, then it's time to ask if you should 
be doing the bottom end.  In all my life with VW diesels, I have only 
_had_ to rering a couple of engines, and that was with over 300K and
over 400K.  

Good luck with your project.


> * the oil should not have done to much harm, but only
> a compression test will tell.  You can not get a
> diesel compression tester for like $40 to your door on
> e-bay, invest in it.  Do a compression test to put
> your mind at ease.  Take time, but worth doing if you
> want it for a daily driver.  Let us know what the
> readings are.
> > > 1).  I found a half container of Valvoline 10W-30
> > oil in the trunk, it's 
> > > a non-diesel rated  oil;
> > > if this is what the PO was running in the engine
> > for its first 2,000  
> > > miles, is there any thing that could or should be
> > done to correct any 
> > > problems that may have caused? ( I changed the
> > filter and put in some 
> > > Shell Rotella 15W-40)

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