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Join Date: Aug 2002
Location: Oxford, England
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changing synthetic oil brands

Hi
You may think this has been covered a zillion times, but I've searched/read many of the threads, but none seem to cover this particular question...
I currently run Shell Helix Ultra 10/40 synthetic in my 65000 mile 1982 930. This coming summer I want to switch to Mobil 1 15/50 (for the slightly thicker viscocity at both ends of the spectrum). So my query is as follows. I am assuming that as oil leaks/consumption are not currently a problem with the synthetic Shell oil, so they won't be with Mobil 1? Is this a fair assumption or will the engine start leaking like a colander?

Old 01-27-2004, 06:41 AM
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According to the Mobil site a tight engine will not start to leak when using Mobil One. It does however insinuate that a leaky engine may seem more "productive". My '85 doesn't leak using Mobil.....some here have different experience.
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Old 01-27-2004, 07:30 AM
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I'm just a hamfisted nuclear engineer, but it seems to me that your assumption should be right. I mean, it makes common sense, right? If you switch from normal to synthetic, the detergents in the synthetics have been known to clean out deposits of normal oil that were keeping the engine from leaking. However, if you're running synthetic already, it shouldn't cause any new leaks.

(shrug) But then I'm just a nuclear engineer who reads to much. I don't really know anything about cars. Let us know how it comes out, will ya?


Dan
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Old 01-27-2004, 08:13 AM
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The info I mentioned from Mobil1.com:

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Old 01-27-2004, 08:35 AM
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My experience with Mobil 1...unless it's an extreme coincidence...does not bear this out. My car leaks with Mobil 1...especially in the colder months.. and actually started to heal itself after I switched back to mineral oil.
--Wil Ferch
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Old 01-27-2004, 10:16 AM
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No doubt, if you have an old car that has been using dino oil all its life, and you change to Mobil 1, there is a chance that the engine will start leaking immediately.

No doubt.

It has happened to me personally (on 2 different old cars), and to lots of others. Don't know how or why it happens, but it did.

Of course Mobil 1 isn't going to want to say that.
Old 01-27-2004, 10:21 AM
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(shrug) But then I'm just a nuclear engineer who reads to much. I don't really know anything about cars. Let us know how it comes out, will ya?


Dan [/B][/QUOTE]

Dan, please stay on the board! If my reactor begins to have cooling problems, you'd be the guy to ask, right???
Old 01-27-2004, 10:22 AM
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I wish this synthetic/dino debate wasn"t such a gray area. I just had a top end rebuild and will be ready for my first oil change(after break in oil) shortly. I keep going back and forth on this depending on what I read.

The car is a 1987 Carrera(84000 m). Any suggestions considering the new rebuild and oil type??
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Old 01-27-2004, 10:25 AM
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I've changed over on a few cars and never had new leaks start as a result.

And no, I don't work for Mobil....I swear.
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Old 01-27-2004, 10:38 AM
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I put 20W50 Mobil 1 in the '86 with 130,000 miles. No new leaks. Actually no leaks at all. My only issue is the cost of adding oil as I burn a bit with this engine.
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Old 01-27-2004, 07:00 PM
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For the first year I had my 911 I ran dino oil and had no leaks.
I then switched to Shell synthetic and I developed a leak onto the passenger side heat echanger within three days. It rarely hits the groud but it does stink and smoke a very small amount.
i just finished replacing the valve cover gaskets, crank case vent hose and gasket, the pressure sender, thermostat o-ring and oil cooler seals, hopefully the leak will go away.
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Old 01-27-2004, 11:31 PM
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Wil and Sam, you need to read the fine print. The Mobil statement says that it does not CAUSE leaks, not that leaks won't result. They very carefully stay away from the statement that if your car does not leak with dyno oils, it won't leak with Mobil 1.

Since I know of Wil's situation personally, I believe it is strictly related to the ability of synthetics to flow more easily, especially in cold weather (which is the only time Wil's leaks - contraction of the seals and or block due to cold?) than conventional oils. I don't recall Wil having the same leak in the summer with the synthetic oil? In any event, if there are leaks you will find them with synth oil where you might not with dino oils. So if you are not leaking with dino oil, but start to leak with synthetics, switch back to dino for the time being.
Old 01-28-2004, 10:54 AM
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Marc ( I mean "Roamer")....you're correct.
The car in question has a quirky winter/summer reversal of the leaking process....car is fairly tight in the summer, like close to "zero"....
---Wil Ferch
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Old 01-28-2004, 02:33 PM
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Fine print = Splitting hairs.
Granted on my engine there had to be a mechanical problem for the leak to develop. Either a bad gasket, o-ring, what ever.
I merely stated that the leak was not apparent when using dino oil but was obvious after switching to synthetic. No, the synthetic did not cause the mechanical problem that eventually lead to the leak. When the synthetic did do was to squeaze through the very small mechanical problem when the dino oil did not.

In conclusion, I agree that sythetic oil will not cause a leak where one does not exist, but it will tend to leak out in places where dino oil will not.

Where I live there is a small temperature swing from winter to summer so my SC has never been run when it was below 55 degrees outside so I don't have a clue if anything I experienced was temperature related.
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Old 01-28-2004, 09:35 PM
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How does one know if the Dino oil one uses contains "seal-swelling" agents? I'd guess the majority do....a result of Dino oils' evolution.
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Old 01-29-2004, 05:33 AM
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Sam,

There is no fine print here, just carefully chosen language.

Old 01-29-2004, 06:27 AM
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