1.8T sludge problem - similar datapoint?

Mike Arman armanmik at earthlink.net
Wed Aug 3 13:59:56 EDT 2005

I'm not sure if this is related, but it might be.

In the 1960s, Shell developed a full synthetic oil for aircraft engines. 
Some of the advantages were low oil consumption, lower than normal wear 
characteristics, and excellent low temperature starting properties. Sounds 
like the answer to a car-maker's dream as well, doesn't it?

Except at about 600 to 900 hours, the oil consumption went way up and the 
compression went way down - Houston, we gotta problem . . .

Turns out the synthetic oil lubricates very well, but is a poor solvent for 
the combustion by-products which dino oil flushes down into the oil tank, 
and go away when the oil is changed. The rings looked like they were glued 
into place with some kind of grey epoxy, which turned out to be lead 
byproducts from combustion.

The new, improved Shell Aviation oil is a mix of synthetics and mineral 
oil, combining the lubrication qualities of synthetic with the 
"housekeeping" qualities of dino.

(This is paraphrased from the 7/22 issue of General Aviation News, article 
by Ben Visser, who worked for Shell for 35 years as a lubricants expert.)

Now we move from history to extrapolation (or if we are unkind, to guesswork).

While the sludge is not lead based (unleaded fuel in cars these days), it 
still needs to be dissolved and flushed out somehow. With only 4.2 liters 
of oil, frequent oil changes are critical - you just don't have that much 
to contaminate, and there's no reserve capacity.

In addition, a cool-down period is needed for turbo engines - Mooney says 
to run the engine at a fast idle for five minutes before shut-down (and if 
you have any idea what an engine for a Mooney 231 costs, let me tell you, 
your hair might be on fire, but you'll wait the FULL five minutes!!).

Possible combination of ways to fix this:

1) more oil capacity, such as an external oil cooler as was suggested 
previously. Adding a quart or two would be a good idea.

2) an after-run fan blowing on the turbo, like the older models had back in 
the days of the type 44s. This would get the turbo temps down so the oil 
wouldn't cook inside of it.

3) selection of oil based on service records of whose engines did NOT 
develop sludge problems

And to implement #3, we'd need a poll/spreadsheet showing miles 
accumulated, oil used, sludge problem yes or no, etc.

Audi, as usual, isn't much help - their products are flawless and never 
require "revisions" of any kind - so it looks like this will be up to us.

Mike Arman
90 V8, not just a car, an ADVENTURE!
(and WELL out of warranty)

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