# Full Synthetic Oil Myth or True



## Baysideblues (Aug 27, 2005)

I was always told that if you put Synthetic oil into a older car with more than 100,000 miles on it that it will leak out off the seals and you will burn it up cuz it will get past the oil rings. 
I was wondering if these is true cuz i was bored and then the Pennzoil comerial came on so I went to there website and they had a section called myths it said that if conventional motor oil doesnt leak neither will synthetic. Does anyone else think that is true. 

Also how about high milage think you could use it?


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## Zac (Mar 10, 2004)

It is a myth. It will not leak.


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## xbrandonx (Mar 27, 2004)

Zac said:


> It is a myth. It will not leak.


I've heard that the detergants in the synthetic oil can do this as well. Maybe not as much to do with the milage of the car, just the gunk thats built up in it.


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## bahearn (Jul 15, 2002)

Synthetic oil CAN start leaking past rubber seals that would stop dino oil. Metal rings are not an issue.


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## psuLemon (Apr 23, 2003)

synthetic oils will clean out yoru motor and will break down deposits from SAE oils. seals like yoru front main and the vc gaskets and other little seals my leak. it will not mess up the rings or anything.


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## Zac (Mar 10, 2004)

Synthetic does not directly cause any leaking. Here are threads explaining the semi-myth.

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=1;t=003808

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=1;t=001455

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=1;t=001432

http://theoildrop.server101.com/cgi/ultimatebb.cgi?ubb=get_topic;f=9;t=000148


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## tom434 (Feb 24, 2005)

In the same vein what about synthetic tranny oil for mt and gear oil?


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## Bror Jace (Apr 26, 2003)

_"In the same vein, what about synthetic tranny oil for MT and gear oil?"_

This myth (current myth) about synthetics came from early PAOs which were not formulated with the needed seal conditioners. This causes seal shrinkage and leaks ... but I'm convinced most of those engines would have leaked anyway.

Well, the better gear oils (say, from Red Line and Specialty Formulations) have a substantial ester content and so I would say would be safe for any unit ... even older ones prone to leaking.


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## Nik33615 (Aug 3, 2004)

Bror Jace said:


> _"In the same vein, what about synthetic tranny oil for MT and gear oil?"_
> 
> This myth (current myth) about synthetics came from early PAOs which were not formulated with the needed seal conditioners. This causes seal shrinkage and leaks ... but I'm convinced most of those engines would have leaked anyway.
> 
> Well, the better gear oils (say, from Red Line and Specialty Formulations) have a substantial ester content and so I would say would be safe for any unit ... even older ones prone to leaking.


I'm not saying anyone is lying but I used Mobil 1 in an NX2000 I had a couple years ago and it did in fact seep out of the valve cover gasket. It wasn't a huge amount but it was happening. After I switched back to conventional oil it did not seep out of the valve cover gasket. That is my experience with synthetic oil. I will also add that the seepage was very minor so the pros of using synthetic oil probably outweigh the cons...


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## Bror Jace (Apr 26, 2003)

*Nik33615*:_"I'm not saying anyone is lying but I used Mobil 1 in an NX2000 I had a couple years ago and it did in fact seep out of the valve cover gasket. It wasn't a huge amount but it was happening. After I switched back to conventional oil it did not seep out of the valve cover gasket. That is my experience with synthetic oil. I will also add that the seepage was very minor so the pros of using synthetic oil probably outweigh the cons..."_

I believe it. However, Mobil 1 is a touch (say 10-20%) thinner than the same weight of typical mineral oils ... especially with the engine cold and sitting. This alone might account for the light weeping you experienced.

My guess is that your NX2000 was on the verge of leaking anyway and the thinness of Mobil 1 pushed it over the edge.

It'd be interesting to see if an ester-based oil like NEO or Red Line would have cause any leakage ... I bet not.


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## Baysideblues (Aug 27, 2005)

Well i think i am going to change my oil tomorrow it has 175,xx on it and i think i am going to try some synthetic oil don't know what kind yet. But i will let you all know. I just want to run it for a while to clean out the motor. I just picked it up so might as well make sure she is nice and clean.


Hey i heard this from an old mechanic i am not sure if he was blowing smoke up my [email protected] but he told me "before you change your oil put a half quart of ATF in there and go for a 10 min drive and this will clean the inside of the motor." I belive some of this is true cuz ATF has alot of clean agents in it but i am still wondering if i should try this or not. What do you all think?


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## pete? (Jul 6, 2004)

i wouldnt do the ATF thing. the mobil 1 will do wonders to your car. i do beleve the myth about it making your car leak. mobil 1 does an amazing job of cleaning your engine and if you have gunky, grimy, or even just alittle grim built up in your engine chances are that its blocked up the gaskets and what not thus causeing them to possibly dry (oil not keeping them lubed) and some times when you switch the synth oil will clean that away and start to leak. this just happend to me with my tranny, i put in red line oil and it leaks but just a very little bit. 

use mobil 1, i did then removed my valve cover and the engine was CLEAAAAAAAAAAAAAAAAAAAAAAAAAAAN!


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## Tavel (Aug 21, 2004)

pete? said:


> use mobil 1, i did then removed my valve cover and the engine was CLEAAAAAAAAAAAAAAAAAAAAAAAAAAAN!


yeup, cleaning goodness. i put mobil1 extended performance in my girls 98 sentra and 3 months later the variabe valve timing problem is substantially lessened. the car now "accelerates" when the throttle is pressed, wow!


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## Bror Jace (Apr 26, 2003)

I guess I can't fault people for wanting to be extra careful about switching a high-mileage car over to synthetics ... but I'd do it. I guess I just have to find (and buy) a high-mileage used car that's been neglected. Hmmm ... not much chance of me doing that. 

It is a myth that ATF contains a great deal of detergents. It is a highly-refined, very thin oil which has been friction-modified depending on the transmission it was intended for. It's cleaning effect is negligible. You could just add half a quart of 5W-30 motor oil ... or 5W-20.

If I want some added cleaning, I'd add a couple ounces of Marvel Mystery oil about 100-200 miles before draining. Safe, mild and seems fairly effective.

I agree that motors run on Mobil 1 seem to stay very clean. Why? Here's why:

1) PAO (Group IV base stocks) tend not to oxidize and therefore produce very few sludge-producing byproducts.

2) PAO synthetics are often blended with Group V esters which are natural cleaners.

3) Oil companies, because they charge more for synthetics, can afford to put the best additive packages in them ... especially detergents & dispersants.


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## tom434 (Feb 24, 2005)

so it wouldnt hurt my 88 pathy 5 speed to switch from dino?


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## Tavel (Aug 21, 2004)

Bror Jace said:


> I guess I just have to find (and buy) a high-mileage used car that's been neglected.



oopsie :loser: . lol. it's getting better though!


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## PoppinJ (Jun 13, 2005)

My understanding has always been that when you use a mineral based oil for long periods of time, it builds up deposits on the inside of your engine. While these are not harmful, they do become an intergral part of your engine. When you switch to synthetic it cleans off these deposits and leaves shit floating around in your oil, small shit, but shit never the less. That is why when you switch, you first use a flushing oil, so you can flush out all the deposits. 

my .02


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## Bror Jace (Apr 26, 2003)

*PoppinJ*, that mostly sounds like the 'false seal' theory. To put it the way I understand it:

Mineral/conventional oils (especially if left in too long) leave deposits that form sludge aound the inside of the engine, especially in low-spots, often against a seal. The actual rubber seal, now cut off from oil splashing against it, begins to harden and/or shrink.

Years later, someone introduces synthetic oil to this motor and the (often thinner) oil with the better detergency begins to eat away at this sludge and expose the old, shrunken seals ... causing leaks.

Sounds plausible. But is that _really_ what's happening in the cases where high mileage motors (at least used) leak when fed synthetic oil?

The idea that synthetic oil would dissolve away old sludge so rapidly that you will have sizeable chunks of junk swimming through your motor seems to me to be wildly overstated. The cleaning effect might be noticeable (oil turns black very quickly) but would likely take 2-3 oil changes with the synthetic oil to do as much cleaning as it's gonna do. It'd be gradual.

The only thing that could dislodge sizeable chunks is an aggressive flush ... and I'm against using those.

So obviously, I think an engine flush before switching an engine to a synthetic oil is unnecessary ... and I am mistrustful of companies that recommend this.


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## Baysideblues (Aug 27, 2005)

Well i just switched my car from a whole life of Standard oil to Mobil 1 full synthetic with 177,xxx miles on the engine. So far there isnt one leak and the car already runs alot better (quieter, smoother) so i hope this keeps going.


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## Sentrixx (Apr 30, 2002)

Baysideblues said:


> I was always told that if you put Synthetic oil into a older car with more than 100,000 miles on it that it will leak out off the seals and you will burn it up cuz it will get past the oil rings.
> I was wondering if these is true cuz i was bored and then the Pennzoil comerial came on so I went to there website and they had a section called myths it said that if conventional motor oil doesnt leak neither will synthetic. Does anyone else think that is true.
> 
> Also how about high milage think you could use it?


 I have been running 10w30 Moble 1 Synthetic on my 99se-l for over 30k miles now. And now its at 105542. Mine you.. I took a smart rout and started with a blend of 10w30 regular and sythetic for 3 oil changes and then when full synthetic. Never saw one problem... Unless you think performance is an issue.


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## Bror Jace (Apr 26, 2003)

Thanks guys, I know that the 'myth' of leaking is based on truth but is blown way out of proportion by most.

While you'll still see the occasional post about current experiences with leaking, most high-mileage engines make the transitional to 'synthetics' just fine. 

That's all I was trying to say.


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