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Discussion Starter #1 (Edited)
2001 530i E39 now has an oil leak after switching to Mobil 1 0W-40 synthetic :eek:

Last owners ran synthetic blend of 5w30, Leak looks like back of engine and front. Front looks to be the oil filter housing gasket and back? I hope it's not my rear main seal.

I'm going to change the oil filter housing gasket but I don't know about my rear main? Maybe i'll try two bottles of AT-205 or drain the oil and fill it back with 5w30 synthetic blend high mileage oil what are your guy's thoughts?

The AT-205 stuff looks good, it claims it doesn't over-swell the rubber gaskets
 

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The oil filter housing leak can result in the whole bottom of the engine being coated in oil. Start with that then see what other issues you may have.
 

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Mechanic in a bottle is seldom a good choice and not much better than mechanic with a bottle! :) Better plan, find where the leak originates and fix it. Not many reports of leaking rear main seals. Might be much easier than you are thinking.

Jim
 

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2001 530i E39 now has an oil leak after switching to Mobil 1 0W-40 synthetic :eek:

Last owners ran synthetic blend of 5w30, Leak looks like back of engine and front. Front looks to be the oil filter housing gasket and back? I hope it's not my rear main seal.

I'm going to change the oil filter housing gasket but I don't know about my rear main? Maybe i'll try two bottles of AT-205 or drain the oil and fill it back with 5w30 synthetic blend high mileage oil what are your guy's thoughts?

The AT-205 stuff looks good, it claims it doesn't over-swell the rubber gaskets
It's possible that the 0W is too thin and it leaks until it gets warmer and thickens. IMO, the 0W oils are for sub zero temp conditions and some of the very new cars, 2010+, are mandating 0W. 5W-XX will flow very well when cold too, but also give you a little more protection/cushion in crtical areas, i.e. valve train and main bearings.

Make absolutely sure you're using an oil that's BMW LL-01 approved!
That's critcal for these cars. On the back of the bottle, it will state whether it meets these BMW standards or not. That's the most important thing, besides fixing your leaks. Not all synthetics are BMW approved. Example, Mobil 1 synthetics are NOT approved. Most Castrol Edge products are. Just read the back of the bottle first of whatever you choose to use. :thumbup:
 

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Since when does oil thicken as it heats?
Since the Germans invented synthetic oil in WW2 I believe. This was the fluid that made the Jet engine viable at the high altitudes they run. Synthetic being one of the few substances that thicken with heat, not thin as most other things do.

Jim
 

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I was under the impression that synthetics behave differently than traditional oil.

Jim
The second number say 5W-30, is the viscosity when it's up to operating temperature, so yes it does get thicker as it comes up to temp.

Synthetic oils last longer before they succumb to thermal breakdown and their useful life is longer than dino oil. They also have smaller molecules than regular dino oil and are basically a better lubricant.
 

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Seems synthetic simply does not thicken as much when cold as dino oil and does not have the oil helpers that wear out with use. Apparently this difference is even greater at lower temperatures approaching zero F, where dino oil turns to dino cement, and synthetics continue to flow. Being most wear occurs at startup this is handy to have around.

Oh crap! Another myth bites the dust!

Jim
 

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The second number say 5W-30, is the viscosity when it's up to operating temperature, so yes it does get thicker as it comes up to temp.
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Sorry you are incorrect. Synthetic oils THIN as they get hotter...and thicken when cold. Please reread the link I provided in a previous thread, which explains how oils (and synthetic oils) work. PLEASE read the first two chapters (though I think when you get into it, you may want to read the entire article ;) ) http://www.bobistheoilguy.com/motor-oil-101/

(since you bashed the link previously because it was on a Ferrari forum, here it is presented on bobistheoilguy forum, that you are familiar with. :)

If you are comparing a 0w-30 to a 5w-30, the only difference is the 0w-30 thickens less when cold. Both will THIN to a 30 weight at operating temperature.
 

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2001 530i E39 now has an oil leak after switching to Mobil 1 0W-40 synthetic :eek:

Last owners ran synthetic blend of 5w30, Leak looks like back of engine and front. Front looks to be the oil filter housing gasket and back? I hope it's not my rear main seal.

I'm going to change the oil filter housing gasket but I don't know about my rear main? Maybe i'll try two bottles of AT-205 or drain the oil and fill it back with 5w30 synthetic blend high mileage oil what are your guy's thoughts?

The AT-205 stuff looks good, it claims it doesn't over-swell the rubber gaskets
Could just be a fluke or unrelated. My car has only run synthetic oil from day one, and has occasionally had leaks I have had to fix (or pay to have fixed) over the years, including valve cover gaskets, vanos gaskets, rear main seal, and upper timing chain gaskets.

If the car leaks, I would fix it...the car is designed to run on synthetic oil, and that is what BMW specifies. "LL-01 approved", specifically. It comes in various weights of 0w-30, 5w-30, 5w-40 and 0w-40 depending on brand.
 

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Actually, that's basically what I was saying. At operating temps, it becomes the second number. When it's cold, at start up, it's the first number: 0,5, etc.
 

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Sorry you are incorrect. Synthetic oils THIN as they get hotter...and thicken when cold. Please reread the link I provided in a previous thread, which explains how oils (and synthetic oils) work. PLEASE read the first two chapters (though I think when you get into it, you may want to read the entire article ;) ) http://www.bobistheoilguy.com/motor-oil-101/

(since you bashed the link previously because it was on a Ferrari forum, here it is presented on bobistheoilguy forum, that you are familiar with. :)

If you are comparing a 0w-30 to a 5w-30, the only difference is the 0w-30 thickens less when cold. Both will THIN to a 30 weight at operating temperature.
Excuse me, but no I was not incorrect!! Per Bob's The Oil Guy: "Viscosity is the thickness or "weight" (w) of an oil. It is represented as a number such as "10w-30." Polymeric thickeners (AKA viscosity improvers or VI's) are added so the oil will thicken as it gets hotter."

That is exactly what I was referring to!
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1146784

Scroll down to the large post with the explanation on VI's and why oil thickens when it get hot.
 

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Discussion Starter #17
Oh f$$k yeah it was only my oil filter housing gasket I guess it was dropping oil enough for it to run to the back of the engine making me think it was the main seal. Since changing it and cleaning up everything with degreaser it hasn't dropped any oil. I'm happy and lovin my e39 again :)
 

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Oils get thinner when they get hotter. The viscosity improvers (VI's) that actually do get thicker with higher temperatures. VI's are what makes a multi-viscosity oil. Although, synthetic is naturally multi-vis (less change in viscosity with temperature than petroleum oil).

The SAE viscosity index numbers are a function (line on a graph) of viscosity with temperature. A multi-vis oil will be below the "W" function at 32F (0C) and above the non-W function at 212F (100C).

Here's a graph of a SAE 5, an SAE 40, and an SAE 5W-40. The VI's flatten out the line, but the line still goes down with higher temperatures.

BMW LL01 is the schnizzle. But, you might get the leaks under control with a short oil change cycle of Mobil 1 "High Mileage" oil. That stuff has special additives that cause rubber seals to soften up and swell up to stop small leaks.
 

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Excuse me, but no I was not incorrect!! Per Bob's The Oil Guy: "Viscosity is the thickness or "weight" (w) of an oil. It is represented as a number such as "10w-30." Polymeric thickeners (AKA viscosity improvers or VI's) are added so the oil will thicken as it gets hotter."

That is exactly what I was referring to!
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1146784

Scroll down to the large post with the explanation on VI's and why oil thickens when it get hot.
Yes, you are mistaken...you may be reading, but not understanding. Viscosity Improvers (VI) help prevent oil from thinning too much, but do not make them actually thicker as temperatures increase.

"Thickeners and viscosity index improvers are polymeric, and are added to lubricants to reduce the degree of change in viscosity seen at high and low temperatures. Mineral oil lubricants become less effective at high temperatures because heat reduces their viscosity and film-forming ability."

Try reading this:
http://www.machinerylubrication.com/Read/1327/viscosity-index-improvers

Better yet, read the first two chapters of the linked article I have previously provided to you multiple times. ;)
It really is a good read...I personally do not believe the writer's promotion of using thin oils, but his explanation of how multi-viscosity oils function is very useful information.
 

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Excuse me, but no I was not incorrect!! Per Bob's The Oil Guy: "Viscosity is the thickness or "weight" (w) of an oil. It is represented as a number such as "10w-30." Polymeric thickeners (AKA viscosity improvers or VI's) are added so the oil will thicken as it gets hotter."

That is exactly what I was referring to!
http://www.bobistheoilguy.com/forums/ubbthreads.php?ubb=showflat&Number=1146784

Scroll down to the large post with the explanation on VI's and why oil thickens when it get hot.
Here is a simple experiment. Start your Corvette up from cold, let it idle..what is the oil pressure reading? Make a note. Go for a drive for 30 or 40 minutes, pull over, and park, with the engine idling. What is the oil pressure now? If the oil was thickening, why is the oil pressure lower when the engine is hot?
 
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