If your engine has been taken care of, there should be no reason why you can't switch to synthetic. If you have no idea what has been happening in your engine, or are changing the oil for the first time in 90,000 miles, then I'd be a bit hesitant. You will most likely experience some blow by as the synthetic cleans the rings and frees them up again, provided the synthetic has the additives to do this. I converted an 89 E-150 van with the 5.0 I once bought with 95K on it, and went through three quarts before the rings were clean and the the consumption stopped.
Synthetics won't cause a seal to leak, but they could expose a bad seal and then it might start leaking. Since most synthetics do clean the engine to some degree, if you have deposits on a bad seal that prevent it from leaking, when they are cleaned away, you might experience one. In some cases the additives used to create seal swell and keep them pliable might refurbish a dry seal and the leak might even stop. If it doesn't, that seal needed replacing anyway. In the early days of synthetic, Mobil 1 got a bad rap for this because they didn't have any of these additives. It did a good job cleaning away the deposits, then ran out of the seals.
No problems switching back and forth, just why step back once you step up to synthetic?
Those oil companies that offer a warranty for running extended drains usually still do recommend the filter changes. Amsoil last fall released new filters designed to go the full one year or 25K mile drains they recommend with most of their oils. These are their Ea Oil Filters. They filter 98.7 percent of ALL partcles 15 microns or larger. I have been using their previous filters, their Super Duty Filter (SDF), for years at the then recommended intervals of 6 months or 12,500 miles, and never had any wear issues. I just switched over last month to the new Ea Filters when I changed the oil in all my cars. Where did you read on their site about the 5000 mile filter changes? Only time I've been aware of shorter oil filter changes with Amsoil is if you are using something other than their filter, which they design for longer use.
One thing to note on the Mobil 1 Extended Performance oils that offer 15,000 mile drains. Mobil does not warranty these drains on vehicles still under factory warranty.
On a side note, Amsoil has been converting their filter lines over to nano-fiber technology that Donaldson Filters developed to combat the fine dust that the M1 Tanks encountered in the mid-east during the first Gulf War. Some of you might be interested in their Ea Air Filters. This are dry filters rather than wet. They are reusable for 4 years or 100,000 miles and you just need to use a shop vac on them after 25K. They flow as well as after market wet gauze filters, but filter 50x the dust. Earlier this week they released a line to replace aftermarket filters called Ea Air Induction Filters. They are pushing to become a leader in the filtration market as well.
Synthetics won't cause a seal to leak, but they could expose a bad seal and then it might start leaking. Since most synthetics do clean the engine to some degree, if you have deposits on a bad seal that prevent it from leaking, when they are cleaned away, you might experience one. In some cases the additives used to create seal swell and keep them pliable might refurbish a dry seal and the leak might even stop. If it doesn't, that seal needed replacing anyway. In the early days of synthetic, Mobil 1 got a bad rap for this because they didn't have any of these additives. It did a good job cleaning away the deposits, then ran out of the seals.
No problems switching back and forth, just why step back once you step up to synthetic?
Those oil companies that offer a warranty for running extended drains usually still do recommend the filter changes. Amsoil last fall released new filters designed to go the full one year or 25K mile drains they recommend with most of their oils. These are their Ea Oil Filters. They filter 98.7 percent of ALL partcles 15 microns or larger. I have been using their previous filters, their Super Duty Filter (SDF), for years at the then recommended intervals of 6 months or 12,500 miles, and never had any wear issues. I just switched over last month to the new Ea Filters when I changed the oil in all my cars. Where did you read on their site about the 5000 mile filter changes? Only time I've been aware of shorter oil filter changes with Amsoil is if you are using something other than their filter, which they design for longer use.
One thing to note on the Mobil 1 Extended Performance oils that offer 15,000 mile drains. Mobil does not warranty these drains on vehicles still under factory warranty.
On a side note, Amsoil has been converting their filter lines over to nano-fiber technology that Donaldson Filters developed to combat the fine dust that the M1 Tanks encountered in the mid-east during the first Gulf War. Some of you might be interested in their Ea Air Filters. This are dry filters rather than wet. They are reusable for 4 years or 100,000 miles and you just need to use a shop vac on them after 25K. They flow as well as after market wet gauze filters, but filter 50x the dust. Earlier this week they released a line to replace aftermarket filters called Ea Air Induction Filters. They are pushing to become a leader in the filtration market as well.