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Is it ok to switch back and forth between regular and synthetic motor oil? Forums > > Is it ok to switch back and forth between regular and synthetic motor oil? Is it ok to switch back and forth between regular and synthetic motor oil?
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  #1  
Old 07-25-2010, 02:00 PM
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Default Is it ok to switch back and forth between regular and synthetic motor oil?

I get this question a lot through PM's and at the shop. My experience is that it does not cuase any harm to the engine, but I also got some answers from the oil companies through their web sites:

Quote:
Switching between synthetic and conventional oil does not cause problems. Because the oils are compatible, you can switch back and forth as often as you like.

Source: valvoline.com
Quote:
The instructions are very easy to follow: Simply change the oil as you would normally. Any “confusion” is just myth. You can switch from conventional motor oil to Mobil 1 synthetic (and back again, if you want), without following any special procedures.

The only exception to this is with a higher-mileage engine that has never used synthetic motor oil, or with an engine that has used conventional motor oil and been poorly maintained. In these cases, you should still follow the same basic oil-change procedures (drain the old oil, remove the old oil filter, put in new Mobil 1 and put on a new oil filter), but you should follow a regimen of one or two shortened oil-change intervals. For instance, let’s say that your regular oil change interval is 5,000 miles. If you’re switching to Mobil 1 under the circumstances mentioned above, make your next Mobil 1 oil change in 2,500 miles, your third Mobil 1 oil change 3,500 miles after that, and then follow your normal 5,000 mile oil-change interval. The reasoning behind this staggered interval is that a high-mileage engine, or one that has seen infrequent oil changes, will likely have a considerable build-up of sludge and deposits. Mobil 1 will help clean the engine as you drive, but it will have to work much harder in a very “dirty” engine, and so it is best to change the oil more frequently for those first few thousand miles. After that, you can rest assured that Mobil 1 is continuing to keep your engine running clean and well lubricated for mile after mile.

Source: mobiloil.com

Quote:
MYTH! Synthetic oil is compatible with conventional and synthetic blend motor oils. You could go back to conventional oil, but you'll miss out on the superior engine protection only synthetic motor oil provides. You wouldn't go from DSL back to dial up would you?

Source: castrol.com
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  #2  
Old 07-25-2010, 03:41 PM
Clint Clint is offline
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Default seal leaks

It's been posted on forums by members who claim they were told that if you switch from synthetic back to dino oils at a higher mileage you seals and or gaskets will shrink and leak. Any truth to this or just another urban legend?
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  #3  
Old 07-25-2010, 04:08 PM
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Quote:
Originally Posted by Clint View Post
It's been posted on forums by members who claim they were told that if you switch from synthetic back to dino oils at a higher mileage you seals and or gaskets will shrink and leak. Any truth to this or just another urban legend?
I don't think there is any truth to that. Both oils have the same compatibility with the seals.
It could be possible to create leaks if you were to switch from conventional oil to synthetic on a higher mileage engine because the synthetics do a better job of cleaning.If they clean out sludge build up around a gasket or seal that wasn't leaking previously it could start a leak.
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Old 09-20-2010, 09:15 PM
Waitingtundra Waitingtundra is offline
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Quote:
Originally Posted by mpe235 View Post
I don't think there is any truth to that. Both oils have the same compatibility with the seals.
It could be possible to create leaks if you were to switch from conventional oil to synthetic on a higher mileage engine because the synthetics do a better job of cleaning.If they clean out sludge build up around a gasket or seal that wasn't leaking previously it could start a leak.
I have also heard this thoery many times, I believe it has to do the mainanence a vehicle has had also.
  #5  
Old 09-28-2010, 09:26 PM
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Default

pretty interesting i always wondered about the switching between oils.
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Old 11-01-2010, 12:42 AM
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It's not like other forums where some attendees tend to be somewhat unfriendly or really have no valueable input to contribute.
  #7  
Old 11-26-2010, 09:45 AM
Pathfinder03me Pathfinder03me is offline
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zhengwei,

Respectfully, you may want to open another topic for your question, as this topic is about something totally different. Thank you.
  #8  
Old 02-02-2011, 02:28 PM
stamarus
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absolutely
If your engine has sludge seals, meaning sludge has formed in the leaking seal

synthetic is thinner and can leak through,
and dissolve the seal.

It says it everywhere including there. A high mileage engine synthetic can cause leakes in.
Yes it has happened to me. ususally the engine is leaking some before and synthetic makes it leak more.
  #9  
Old 03-10-2011, 05:49 AM
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So, what is considered high mileage. I have ~73K on my Frontier and have changed oil every 3000 miles. I have thought about switching to Mobile 1, but felt I let my mileage get too high.
Then, on the other side, I just bought a Murano. At what mileage should I wait to switch to Mobile 1?
And why would somebody want to switch back and forth?
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Old 08-17-2011, 06:10 AM
ShawnH ShawnH is offline
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So what is considered high mileage? i have 40000 on my Altima (08), is this to many miles?
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  #11  
Old 08-17-2011, 12:42 PM
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"Cint" - your question is perfectly answered by Mod mpe235. That is the only possible consequence if you did not have a decent regular oil change.

When I hit 90k a few months ago I switched to Castrol full synthetics. It's been almost 5k miles now. The oil still looks very good and I never had the need to add oil. Just a tad darker. I plan to initially change at 7.5k mi. With that I used FRAM high mileage oil filter.

I think at 75k is considered high mileage. At least that's what I see in makers of motor oils, oil filters and other stuff.
 

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