Jay H

This may be a stupid question, but I'll ask anyway...

I recently spoke with the prior owner of my '90 964 and found out that he had been using Mobile 1 15W XX in the car since it had 6000 miles on it.

I obtained the car last fall when it had 28,000 miles on it and promptly changed the oil to regular dino 20W 50 (I did not know at the time Mobile 1 was being used). I put about 300 miles on the car before it had to go into storage for winter. I changed the oil and filter once more at 28,300 miles after it was brought out of storage this spring. Again I used dino 20W 50 oil. The car now has 29,000 miles.

I've read and thought that going from regular oil to synthetic may give problems from leaking seals on some motors. But, I'm wondering if anything can happen from going from synthetic back to regular oil?

The previous owner had the synthetic changed every 2000-6000 miles prior to my ownership.

How dumb of a question is this?

Thanks for any help,
Jay
90 964

Bill Wagner

Jay:

That's not really a dumb question at all. An old tale about synthetics is that once they're used in cars running "regular" oils, owners run the risk of leaking at seals. I think there may have been some basis in fact for this when synthetics were still fairly new (decades ago), and there may still be some basis in fact for this with cars that have been using "regular" oils for very high miles (hundreds of thousands of miles over a long period of time). In the latter case, "gunk" from the old oil can apparently form around seals and actually prevent them from leaking. Once synthetic is added, it's higher detergent concentration tends to clean this gunk out and leaks appear.

I'm NOT going to swear that any of the theories I've just re-gurgitated from other web sites is true or not, but it does make at least a little sense.

I wouldn't be afraid to put synthetic in your car at all.

Jay H

Bill:

Thanks for the reply. I've read too that if you switch from "regular" oil on certain higher mileage motors to synthetic, you can cause leaks.

What about if the car has had synthetic used most of it's life and now I want to switch to using "regular" oil?

Thanks,

Jay

Bill Wagner

Jay:

Switching from one to the other should be no problem at all. In fact, I think I read on Mobil's web site that you can actually mix the two different types of oils (synth and dino) without a problem. Problems arise when people start just mixing grades like 0W-30 and 20W-50 without regard to a cars requirements. Never the less, I don't think I would deliberately mix synth and dino together unless it was an emergency.

Good Luck,

Bill Wagner