Mobil 1 15w-50: Extended Performance (Gold Cap) vs. Silver Cap, Formerly Red Cap

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15 Nov 2012 10:29 #12562 by Kiln_Red
There has been an evolving conversation going on concerning Mobil 1 15w-50 and its ZDDP levels recently. The discussion started here and it has since migrated to Rennlist. There have been a number of suggestions that Mobil had recently tweaked Mobil 15w-50 in a way to conform to GL-4/GL-5 standards. This is not entirely accurate. For a time, there was a product called Mobil 1 15w-50 Extended Performance (Gold Cap) that was readily available and it is true that this formula followed GL-4/GL-5 standards. ZDDP levels exceeded no more than 800ppm; not suitable for our flat tappet lifters.

Before the emergence of this new formula, Mobil only offered one oil of the same viscosity. Mobil 1 15w-50 (Red Cap) which has since been replaced by Mobil 1 15w-50 (Silver Cap). This is an entirely different oil. The only thing it shares with its Extended Performance couterpart is the viscosity. To my knowledge, the red cap formula and the silver cap formula are the same oil. Both the silver and red cap M1 15w-50 are specifically formulated for older flat tappet lifters such as our 928 engines. ZDDP level is 1300ppm; suitable for our engines. When the Extended Performance formula hit the shelves, many say that M1 15w-50 became increasingly harder to find or that it was removed from the shelves entirely in some areas. It appears safe to assume that this was to market the Extended Performance oil of the same viscosity. A lot of people apparently blew the whistle or cried foul considering that Mobil was practicing bad ethics for this marketing attempt if that's what you want to call it. That is your opinion to make.

It is obvious that many folks in the 928 community do not know the specifics of the different formulas. Clearly, they are different formulas. That is all that I wish to highlight. I am not endorsing Mobil or any other oil brand. My only motive has been to get the facts as this conversation has evolved. Many of you may have already known this information. My suspicion is that many of you did not.

If you have any doubts about the oil you are using and its ZDDP content, I would suggest getting an MSDS unless the information can actually be found on a container or the manufacturer website. There are many oils suitable for the 928.

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15 Nov 2012 18:17 #12570 by mm928
Thanks for that Austin, good to know. In your experience have you heard of issues going from Dino to Syn in 16v engines? I do not have leaks that currently require immediate attention. I never have to add oil before my yearly change. Just wondering about that part should I try Royal Purple or M1 Silvertop.

1983 928S - 16v 4.7L L-Jetronic
Dark Grey w/ Blue Leather
85/86 exhaust manifolds
Y-Pipe
SS Hi-perf Cat
S4 springs
Bilstein shocks
Air pump delete
VIN: WP0JB0926DS861180
- - Isn't Life great? - -

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15 Nov 2012 18:30 #12571 by Kiln_Red

Thanks for that Austin, good to know. In your experience have you heard of issues going from Dino to Syn in 16v engines? I do not have leaks that currently require immediate attention. I never have to add oil before my yearly change. Just wondering about that part should I try Royal Purple or M1 Silvertop.


What dino oil are you using now? My experience with non P cars is that it is critical to know what oil was used originally. I'm sure Brad, Wally, or any other mechanics here would agree.

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15 Nov 2012 22:00 #12574 by 928mac
I am not stuck on any one brand as long as it meets or exceeds the manufactures requirements.
ILL dump anything in my tundra :p

When I first brought my 928 home and found the forums on the net, I remember seeing the threads on USE THE RIGHT OIL
I can not remember where but I followed some links and did some searches and read where some oil brands are rebuked by Porsche.
I had to laugh at the mobile comment as EXXON is one of the main owners where i work.

I did not know about the requirement for high ZDDP at first,
but by reading what I found on the net and what some of the long time Porsche owners have posted,
then comparing that to the advice of the guys in the lab at work,
I decided that If I do not follow their best practices, I will be buying new cam-shafts at the very least.
did I mention that as of Oct. I review and advise to all the oil samples at work (now that can get boring, but it is very critical)


Last year when I was ready to bring it out of storage,
I could not find any oil up hear that met the requirement of 1100 or more ZDDP,
well not normal automotive oil that is, ...
so I used diesel truck Amsoil because it is high performance oil
but just has a lot of detergents in it but met the high pressure requirements.
I think I ran it for around 3 weeks until the Z-rod Amsoil came in.

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It drove me nuts, and I babied the car.
Ya it cost me $150 for oil and filter that I dumped after 3 weeks
But thats better then 3G for cams that get burnt or pitted from the friction .

The other issue with these cars is how hot the engines can get and the high oil pressure.
If you run to thin of oil, not only will it not cool as well, but you will be pumping more then you need into the valve covers.
I do not say that I understand why the pressure is so high compared to other high performance engines or what will exactly go wrong if you use wally world oil, if anything, Just saying that I wont run cheep stuff in the 928 because its just to dam hard to get parts for and to expensive to repair.

I think there are lots of good oils out there, Royal P, The big Q, Mobil,Castrol Motor Oil, or anything that meets the viscosity and pressure requirements

The above is just 1 guys opinion ;)

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15 Nov 2012 22:15 #12575 by Kiln_Red
I think you are absolutely right on all points, Brad. Both as it concerns oil suitable for the 928 and as an assessment of oil in general.

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15 Nov 2012 22:22 #12576 by the flying scotsman
Glad the ZRod is working out for you Brad.

I drove the GTS to Witchita and back in 100F temps, 6000kms in 10 days, never used a drop :)

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