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Discussion Starter · #1 ·
Sorry if this has been asked before but I've always wondered if I should try Synthetic oil on my xc70 which has now 128k. Has anyone done this more recently? Just concerned that it may develop oil leaks. I am told that Synthetic oil technolgy has improved whatever that means.
 

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newer cars with better gaskets have no issue. This story made the rounds decades ago with the introduction of synthetics because some older cars did, Personal experience with my 1987 Monte Carlo and a 1975 Honda motorcycle did, in fact, begin seeping oil when i tried mobil one and stopped when i went back to conventional. Theories centered around the fact that conventional oil swells older gaskets and synthetic didn't and/or synthetic molecules are uniformly smaller.
regardless, it's fine.
 

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On my last oil change I switched to Mobil 1 0W40 euro spec based on some recommendations from some people here. I love it and just bought more to do another change. I have 117,000 miles on my 02 V70XC.
 

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that rumor bothers me so much

use the same weight/viscosity and you will be fine
 

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I run Rotella T6 or Delo XSP 5w-40 in both my V70XC and my SLX. They have been the best oils I've ever ran. Running diesel oil stopped my oil leak and valve tick on my SLX that existed for over a year for the previous owner... It's SN rated. And 18 wheelers run 25000 miles between oil changes so it has to be good!
 

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So I recently switched to synthetic (about 6k kms ago) and I now have an oil leak. But to suggest this was caused by the synthetic oil would be silly. From my perspective high mileage cars (mine at ~230k km) need maintenance and the odd oil leak is common. Likely a lower seal on the passenger side of the motor. Will get that sorted this week and be good for another 200k!
 

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The biggest reason why someone WOULD develop an oil leak switching to synthetic is because the higher quality oil cleans the build up off the engine and seals, thus allowing oil to seep past. This just means you needed to service your engine anyways...
 

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Discussion Starter · #11 ·
I run Rotella T6 or Delo XSP 5w-40 in both my V70XC and my SLX. They have been the best oils I've ever ran. Running diesel oil stopped my oil leak and valve tick on my SLX that existed for over a year for the previous owner... It's SN rated. And 18 wheelers run 25000 miles between oil changes so it has to be good!
Yes I agree. I have a 96 MB C220 with 330k miles. Had a tick. I started using 15W-40 and it disappeared.
 

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I'm at 256k miles, switched to synthetic when I got the car at 79k miles. Doing PCV at 79k I could tell it was a base oil before that.

Synthetic oil does not kill seals/gaskets. But be careful with engine cleaners/flushes, better avoid them.
 

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Old information that’s no longer relevant.

Synthetic is always better than conventional.

These cars like Mobil 1 and Castrol.

I personally run 0w40 full synthetic euro meeting MB229.5 and BMW LL1.

The switch was made on 6 different RN whiteblock turbos and every one exhibited less oil consumption afterwards and over 5 years, no unexpected external seal leaks.
 

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Full synthetic. Driven Racing Oil DT40. Car c30.
Full synthetic Rotella T 15/40. One ton Chevy Express.
Full synthetic Mobil 1. Fiat Abarth.




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Discussion Starter · #15 ·
Thanks for the responses.
 

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newer cars with better gaskets have no issue. This story made the rounds decades ago with the introduction of synthetics because some older cars did, Personal experience with my 1987 Monte Carlo and a 1975 Honda motorcycle did, in fact, begin seeping oil when i tried mobil one and stopped when i went back to conventional. Theories centered around the fact that conventional oil swells older gaskets and synthetic didn't and/or synthetic molecules are uniformly smaller.
regardless, it's fine.
Engine tolerances got very tight in the 90s by the time OBD-II became mandatory. Synthetic is cracked from crude in a way that makes it uniform and consistent. Think of traditional oil as lumpy oatmeal and synthetic as a finely-whipped batter. Now think of old carbureted engines from musclecars and old trucks and how oil blow-by pretty much meant they were adding oil between oil changes b/c it was entering the combustion chamber and being consumed. No wonder you were supposed to get your oil changed every 3000. It was a mfr safeguard. In replacing the oil every 3000, the crankcase never actually got so low that it starved the oil pump. Malaise Era at its best!
 

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The oil that will cause leaks eventually is the high mileage etc synthetic oils, I’ve seen people say they actually do swell gaskets etc to compensate for high mileage but when switching back to regular full synth there may be leaks.


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I searched this topic after a friend of mine was going to do the same on an older vehicle. He found credible citations indicating YES synth oil in an older engine can cause leaks. There are credible sources of internet info indicating that YES synthetic oil added to an older engine can cause oil leaks. Suggest staying with old Dino oil. Just use a good quality brand.
 

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I searched this topic after a friend of mine was going to do the same on an older vehicle. He found credible citations indicating YES synth oil in an older engine can cause leaks. There are credible sources of internet info indicating that YES synthetic oil added to an older engine can cause oil leaks. Suggest staying with old Dino oil. Just use a good quality brand.
No. He can use synthetic. It will not cause leaks.
 

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Discussion Starter · #20 ·
Took the leap and did it. I realized I was using semi- synthetic all along. Started with 5w30 high mileage full syn. But next one will be 0w 40. So far so good.
 
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