Hey Smokey

So are you saying that semi-syn oil is recommended as that is what Subaru Osborne Park filled my car with for it's first service?

They recommend non-synth :)
Not certain of their preference between semi and full mineral however.

The following is my 2c

Synthetic oil WILL ALWAYS outperform ANY mineral based oil in ANY application. If you want to bed rings, select a synthetic with a low molybdenum content to allow the rings to bed. If you want to gain kW select a synthetic with the lowest viscosity, if you want to reduce blowby and burning of oil on an older engine select a synthetic with a higher viscosity etc etc etc remembering that any given synthetic will retain the properties for which you purchased it for a longer period of time and under more extreme conditions than a comparative mineral based oil.

Why do manufacturers supply 99% of all new cars with mineral based oil? Because it is cheaper, and producing and selling cars for the highest margin possible is their business. If they can save even $5 per car by NOT using a synthetic oil, a company only has to sell a few million vehicles worldwide and you begin to see my point.

I purchased my car brand new in 2000 and dropped the oil rather promptly after 1000Km.
I sent a sample off to the Castrol Australia Oil Analysis Laboratory just to see how it would come back (my job entails sampling oils from various machines so I just slipped mine in with the rest of the samples) and it was rather shocking.
The total Fe was over 400 but most worrying was that the PQ index, (which measures particles of Fe over 100 microns in size) was elevated to the point where the sample was returned in the alert status. For people unfamiliar with oil analysis samples and the various components that are reported, basically my sample showed that alot of fine iron, and other metal particles, were being stripped from the various running surfaces of the engine.......as one would assume after only 1000Km. I had the make up of the oil verified as a mineral based 20W-50 of unknown brand.

I then replaced the oil and filter with Mobil 1 5W-40 and have changed both oil and filter EVERY 5000Km

The second sample at 5000Km returned near perfect readings with the minute amounts of Fe detected described as residual contamination and a PQ index of 0. the third and final sample that i had tested at 10000Km was again perfect. The car has now done 200000Km. Just to satisfy myself I pulled my rocker cover off last weak to inspect for any signs of valve or cam wear and performed a compression test....... PERFECT

Was my engine simply bedding in for the first 1000Km? if so why did subsequent oil samples failt to show a declining rate of wear? Was the high PQ index a result of the mineral based oils failure to provide adequate protection?

We could debate this all night long.......

My engine is absolutely stock mechanically except for an exhaust and airfilter and I doubt that any mineral based or semi synthetic oil would have provided me with such a well kept engine.

I remenber back when I did my apprenticeship a former Maintenance Superintendant once told me that a good oil is the cheapest insurance you can buy. I dare say he was right.

Please everyone have a good read of these links to understand the background of bedding in piston rings to a honed cross hatched cylinder bore.

Yes this is written from a motorbike perspective but the same principles apply to a WRX EJ engine.

[url]http://www.mototuneusa.com/break_in_secrets.htm[/url]

[url]http://www.rexnet.com.au/forum/index.php?showtopic=63909&st=0[/url]

Taken from mototuneusa site:
Q: If break- in happens so quickly, why do you recommend using petroleum break - in oil (mineral) for 1500 miles ??

A: Because while about 80% of the ring sealing takes place in the first hour of running the engine,
the last 20% of the process takes a longer time. Street riding isn't a controlled environment, so most of the mileage may
not be in "ring loading mode". Synthetic oil is so slippery that it actually "arrests" the break in process before the rings can seal completely. I've had a few customers who switched to synthetic oil too soon, and the rings never sealed properly no matter how hard they rode. Taking a new engine apart to re - ring it is the last thing anyone wants to do, so I recommend a lot of mileage before switching to synthetic. It's really a "better safe than sorry" situation.

J