Synthetic Myths!!
As long as your seals/gaskets are in health.
You can switch to Synthetic Oils ANYTIME!
In an issue of hemmings last year they had a 1957 Corvette with an engine that was rebuilt once 2O years ago. They switched to Mobil 1 and tested the consumption and leakage. Needless to say consumption was negligible (1qt/3000miles) and the leakage was not to different from dino oils.
Case #2
My parents have a 1993 Oldsmobile Ninety-Eight Regency Elite full size Sedan with the 3800 Series I V6. It was run with sometimes regular and sometimes neglected oil change intervals on dinos from factory all they way to the Summer of 2000. At that mileage of 151,000 miles the engine never had a problem and was still very smooth.
After doing a lot of reading I switched to an OTC Mobil 1 TriSynthetic 10W30. I thought running the Royal Purple I use in my Camaro would be overkill *lol* Anyway here is where the interesting stuff starts:
I did add 2Qts of Gunk Motor Flush to engine before the Mobil 1. After the oil change and within 4days of driving the Mobil 1 looked a NASTY jet black and was gritty. The oil smelled like tar!
We changed the Mobil at 2000miles. The same thing as described by the 1st oil change happened.
By the third Mobil 1 change the oil essentially looked normal. We usually follow the engine oil life monitor and depending on conditions that means a change every 4-5k miles.
Leakage actually decreased since spotting on our driveway is not as much as before. The oil looking like tar and nasty....my assumption is all the years of skank and crud from the dino oils got solvated and cleaned off by the Mobil 1 (or much of it at least!).
When in doubt I woudl invest in Auto-RX (via two treatments with dino) as a means to pre-clean your engine before your introduce the aggressive synthetic oil chemistry.
That was nearly three years ago and now the "Old-Faithfull" 3800 Engine has 181,000 trouble free miles. Funny, all the mechanics "in-the-know" told me it would be a grave mistake to change at such a late point!!!
LOL
Sunil-