Switch To Conventional Oil?

Discussion in 'SN95 4.6L Mustang Tech' started by bhuff30, Jun 21, 2014.

  1. My gt has gotten Mobil1 since around 40k miles. With over 222k miles now, the valve seals are a little tired. I get the tell tale puff of smoke leaving a long stop light or on a hot start after sitting a bit, and it is worse in the summer.
    I have heard synthetics, and particularly Mobil1 find any leak worse than other oils. Do you think a conventional would give me less of a smoke show?
    It doesn't consume a lot of oil, maybe a quart every 1500 to 2000 miles, but it is a bit embarrassing to leave the smoke.
  2. Mobile One finding every leak is what I've always heard, (and that has been my experience too, the couple time I tried Mobile One. But that was years and years ago).

    maybe try an oil change with Motorcraft semi-synthetic or something like that and see if the makes any difference?
  3. You go up to 10w-30 in these engines, make sure it's still synthetic though. I've ran 0w, 5w, and 10w in my 4.6 mod. 0w in the winter . And the thicker oil in the summer. All with no problems. Now these vortec 5.3 liters; by GMC, do not like the 10w, starts engine valve train knock. Nice to have an all purpose motor.
  4. I have been running 10W-30 in my 4.6 for a while now. I used to run thinner oil in the winter, but gave that up a few years back with the higher mileage.
    I like the idea of a motorcraft semi-synthetic. I would probably feel ok going 5k miles on that. I usually put 7k on mobil1 before changing it.
  5. Try that Lucas addictive.
  6. I run Shell Rotella T6 5W40 (yes, "diesel oil") in my 2010 STI and am tempted to run the stuff in my MGT on its next oil change. If you're burning oil and have cats though, this may not be a good idea as the elevated ZDDP in the Rotella may injure the cats over time...

    For tired valve guides you might also try one of those "old school" tricks and add some automatic transmission conditioner to the oil. Those additives work to swell seals slightly giving at least temporarily better sealing. Not sure if the material used in the seals of the 4.6 would respond to that stuff in this way though.

    If you're adventurous you might think about replacing the seals for each of the 8 cylinders. You could also check the valve stem to guide clearance (just wiggle things) to see if you need more extensive surgery.