How much ZDDP is in your Porsche?

By James Renfrew

If you care about the longevity of your motor, especially the air cooled motors, you should know what I’m talking about.

Since the catalytic converter was introduced oil manufacturers have been reducing the amount of ZDDP, or Zinc dialkyldithiophosphates, in their lubricants.  Most off the common off the shelf oils now contain less than 800PPM versus 12-1400PPM that was found in oils of the 1980’s.  ZDDP is particularly important on Porsche motors that have flat tappet cams or non-ceramic valve train.  That’s you Mr. Air-cooled and other vintage water cooled guys.

Porsche recommends Mobil 1, so it’s safe…  Right?  While Mobil 1 is now starting to increase it’s levels of ZDDP in their higher end  oils again, the general consensus of Porsche engine builders is no.  Having done a lot of research myself and always been a Mobil 1 fan, I’m not convinced it’s the best choice for my vintage cars anymore. There are oils available now that don’t cost anymore but offer superior protection.  Porsche has had ties with Mobil oil going back over 30 years now and as such it’s not a tie they would break easily.  Which is why I suppose Porsche still recommends it for vintage Porsche’s and supplies it in the motor of every new Porsche too.  But that’s my own personal conjecture.

The top two favorites among Porsche engine builders today seems to be Swepco 306, specifically 15W40, and Brad Penn 20W50.  While the Brad Penn being the most expensive, I did find a comparison guide between Mobil 1 and Brad Penn.  Out of 50 oils tested, it put Brad Penn only one notch up from Mobil 1.  Unfortunately the same guide did not compare the Swepco oils.

Is your vintage Porsche equipped with a catalectic converter(s)?  You might want to stay with the Porsche recommended Mobil 1 oil simply because high levels of ZDDP reduce converter efficiency.  Mobil 1 still offers some of the highest ZDDP levels available off the shelf, but not as high as say the Swepco or Brad Penn.  Which would still make the Mobil 1 a better choice than “the other guys”.

New motor in your vintage Porsche?  You should be VERY concerned about the ZDDP levels.  Running a modern low Zinc oil could destroy the motor within hours.  There are break-in oils specifically formulated for you.  Alternatively running a race formulated or other similar high ZDDP level oil is ideal for your new motor break in period.

While ZDDP isn’t the end all be all of motor oil performance, it’s a significant factor in the longevity of older motors.  Newer engine designs with roller cams or ceramic cam components are specifically designed to run with lower ZDDP levels and as a result are not typically affected by running low ZDDP oils.

*Update* This past summer of 2014, Porsche now offers their own line of oils for older Porsche cars.   However it’s very pricey even with the club discount.  Just the oil on my 928 was over $150 so a 911 I imagine will run you roughly $200.  I’ve seen some chemical analysis reports of the Porsche brand and they do have significantly higher levels of ZDDP than “the other guys”.  But still not quite as high as some of the quality race oil brands I’ve mentioned in the original article.   It’s certainly a great choice for your car, if not your wallet though.

James Renfrew
VIR South Island Director

Reference material for this article…

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