Contour Enthusiasts Group Archives Forums Modifications Duratec Maintenance Anyone use motorcraft oil?

Originally posted by tktrain:

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Originally posted by my csvt:

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Originally posted by tktrain:

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The synthetic is so slippery it will go right past the seals.

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the reason is the detergents in full synthetics do a much better job of cleaning out the crap that "assist" older engines with less good(bad english, i know) seals. when all this crap is swept away the old seals sometimes are not able to properly and/or effectively perform their job because all that crap was a barrier for the oil. a high mileage engine with good seals will have no problem with leaking at all.

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I switched from dino to full syn at 120,000 miles. I had experienced no leaks from the day it was delivered new. I am the original owner and religiously changed the oil and filter at 3000 mile intervals with Motorcraft, I have the receipts from my local Mercury dealer "quick lube" service to prove it (at the time it was my company car, and they paid for all service). As soon as I put the 5W-20 full syn in it, I started seeing oil spots on the garage floor. I went 6000 miles total (an oil filter change at 3000) with the full syn and had to add a quart after 2000 miles. I then switched to 5W-20 syn blend and the leaks went away after about 500 miles. Shortly after this I heard the Saturday morning "Click and Clack" show on PBS radio talk about this very subject of switching high mileage vehicles to syn. They related the leak past the seals scenario. After hearing the same explanation from them and a lubrication engineer I used to work with at International Harvester's Advanced Engine Design group in Melrose Park, Illinois, I believe that it is likely true. He said seals wear slightly over the extended mileage with the dino, and that they can thermo set a bit from heat cycles. The full syn can simply work it's way past them. Kerr-McGee Petroleum's chemists also have published research that says basically the same thing.

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