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Cadillac Northstar Engine Woes and Fixes
I was using Amsoil 15-40 heavy duty marine diesel synthetic oil.  It seemed to lesson the oil burning but the leaks persisted.

I then found Auto Rx and as per instructions switched to conventional dino oil.  I run Chevron 15-40 diesel oil or Castrol 20-50 motor oil.  I went the route with the RX and did one bottle the first time as I was nervous.  After running it and changing to just oil, I noticed the leakage had cut way back.  I then ran the RX again with a double dose of two bottles and noticed the oil leaks had ceased 100%.  Next oil change was with no RX and the leak started again but not as bad.  Next oil change I used one bottle of RX as a maintenance does and the leak is negligible.  I've experimented back and forth between conventional oil and synthetic oil both with and without RX.  I've even tried 6qts of conventional and 2 qts of synthetic and it leaks.  For some reason the synthetic gets past the seals.

With synthetic oil I get leaks even with two bottles of RX.  With Dino I get none with RX.  The car has 110k miles and I do change oil frequently.

I had written about this on the NorthStar board a little over a year ago as most people with a used NorthStar cannot afford to replace the seals.  GM has since changed the material of the seals.  I believe it was the crank case half seals and/or oil pan seals.

I did not realize the engine was designed to burn oil when I purchased it.  I would guess it used one quart in 600 miles when I first purchase it and now is 1,000 to 1,500 miles.  Interestingly it burns less with synthetic than conventional.  I never have seen blue smoke, only black so I'm not sure how and when it burns it off.  My oil still is clean at 5,000 miles but I change it anyways.

I am also using the RX in a Volvo 240 and E305 diesel one ton.  The only leaks I see now are from the powersteering pump which is notorious on the Fords.  Also using it in a 10hp snowblower but since you are in Florida you have no idea what those are used for and won't believe me if I tell you!

 I have no explanation or theory.  I'll be doing another oil change in the next few weeks and will go with one bottle and straight conventional to monitor.  I like using a little synthetic for the ease in starting in the winter but will hold off to let you know.

 Thanks

Charles Bennett
Chambersburg, PA

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