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I have heard numerous people say once you put synthetic in your motor, you can't go back to regular motor oil. Others have told me it makes no difference. So what's the real deal? :dunno:
 

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Sure you can switch back and forth just don't mix dino with synthetic:thumb:
 

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I'm not sure about diesels but I know it's bad to shift a high mileage gas engine over to synthetic. This is widely argued but in my experience I've had two engines start leaking at the seals. Both were over 90k miles.

If someone has an opinion about shifting a 230k mile diesel over to synthetic I'd like to hear it... :)
 

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Go for it... Switch back and forth, to and fro... it makes no differance.
 

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The ones that leaked:

2000 Toyota Sienna with 90k began leaking from valve cover. I switched it back to dino and the leaks stopped. I love this van. It's always had 3k oil changes and now at 110k, even when I pull the dipstick at 3k on the oil the oil looks as clean as brand new.

1999 Toyota Corolla with 130k began leaking from valve cover and something else that I can't remember. It was pretty significant, though, as it made a very clean engine look really oily. The reason for this was the detergents in the synthetic oil cleaned up the seals which had been 'sealed' from oil by all the deposits. Once they saw oil again the cracks that were there (but sealed) now started leaking. I switched it back to a high mileage dino oil but sold it before I could get much more data.


I will switch my 7.3 sometime before winter to synthetic, then. I definitely want the added protection from a synthetic oil before I head to New England for the winter.
 

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My understanding is it does no harm to switch but that you need to keep an eye on it afterwards and if it is burning or leaking than you need to switch back to regular.
 

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I'm not sure about diesels but I know it's bad to shift a high mileage gas engine over to synthetic. This is widely argued but in my experience I've had two engines start leaking at the seals. Both were over 90k miles.

If someone has an opinion about shifting a 230k mile diesel over to synthetic I'd like to hear it... :)
the leaks were because the synthetic cleaned the gunk out. the l;eaks were there, they were just clogged up.
 

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I have heard numerous people say once you put synthetic in your motor, you can't go back to regular motor oil. Others have told me it makes no difference. So what's the real deal? :dunno:
switching doesn't hurt, like others had said. the only thing I would do is try to stay with a CI-4+ oil as opposed to CJ-4.

any particular reason why you want to switch?
 

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You can mix them, switch back and forth, its doesn't matter. However the thing to remember is, if the oils are mixed you only get some of the benefit of synthetic.
 

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Discussion Starter #12
any particular reason why you want to switch?[/QUOTE]

I had switched to Syn. in my 95 and really like the performance and ease of starting I experienced over the cold months. I plan on doing the same with the "00", partially to see if we can bring the fuel mileage up a little.

My reason for posing the question was a comment made by a mechanic friend. When he found out I had sold the 95, knowing I had changed to the synthetic oil, he wanted to know if I had informed the car lot or the new owner. I had informed the car lot, but since I wasn't camping out to see who bought it, I hadn't informed the new owner. He seemed really concerned that the engine would be destroyed if the guy put dino back in it.

The guy who does my oil changes told me, basically the same thing all of you have imparted here. A certain amount of the old oil will remain in the system until it has gone through a couple oil changes, and as long as it's lubricated, the engine doesn't really know the difference. Makes sense, but this also coming from a guy whose business relies on people like me paying him more money for synthetic, and wanting to keep my business if I decide to return to dino. :)
 

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I would be thinking twice as to return to this guy or not.
 
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