lehmkuhler

Does anyone have the time to give me the skinny on oil viscosity. I have been given a number of opinions about what to use. My mechanic (non-dealer) said to use 20W-50. Car is driven about 20mi five days a week.

Thanks,
Monte '91 C2

Kevin

Monte;

I have had good luck running Mobile 1, 15w-50 in all my 911's. Besides it is the factory oil of choice.

Jim Michaels

I run the same oil that Kevin does, but our common preference doesn't necessarily make your mechanic wrong (Check your owner's manual). Modern 20W-50 dino oils apparently also do a good job in relatively mind winters (VA). If you lived in MN, you might want to go to 10W-30, or an even lower first number. Some use a 10W-30 in winter and a 20W-50 in summer. Mobil 1 now makes synthetic 0W-somethings.

Drew_K

I would also go with whatever the manual recommends, which is probably 15W-50. As compared to 20W-50, 15W-50 will flow better at startup which is a critical time to protect from engine wear.

Here's why (in case you didn't know): Viscosity is a measure of thickness, or how well a fluid flows. A higher viscosity means the fluid doesn't flow as well. Picture honey; very viscous.

For rating purposes, an oil's viscosity is rated at two different temperatures, 0 and 210 degrees F (low and high temperature). If an oil meets the SAE standard for flow at low temperature, it is given a "W" and a rating (e.g., "10W"). The second number is its rating at high temperature (e.g., "30"). Thus, "10W-30" oil, with the first number being the low temperature viscosity rating and the second number being the high temperature viscosity rating.

Some oils do not meet SAE standards at low temperature and therefore do not get a "W" rating (e.g., straight 30 weight oil). Also, oils that have both a high and low temperature rating are multiviscosity oils, indicating the oil is actually a blend of two different viscosity oils.

Between a 15W-50 and 20W-50 oil, the 15W-50 should give better protection at startup because it has a lower cold temperature rating. The lower the rating, the more easily the fluid flows. A "0W-xx" oil would give even better startup protection but may not be good at high temperature.

That's my best recollection of oil ratings. Anyone please feel free to jump in and clarify/correct me.

Drew
92 C2 Coupe

BradfordD

Monte,

I also have had good luck with Mobile 1 15w-50 (Porsche's factory oil)... However I have recently changed to Swepco #306 15w-40 on the recomendation of my local speedshop. Based on mild winter and weekend driving... Seems to be running very well cold and hot, and I am not adding as much (less than a quart in 1,500 mi so far).

John K

I've never heard of swepco oil. Where did you get it and how much was it?

BradfordD

John,

Got mine from S-Car-Go Racing in Marin County (they're the local distributer) 415-485-6026. Purchaed by the case, it works out to $6.25/Qt... Here's Swepco's website...

<a href="http://www.swepcousa.com/lubesite/highperf.htm" target="_blank">http://www.swepcousa.com/lubesite/highperf.htm</a>

Happy Trails,

Young_Turk

Great, while we are talking about oils.
I am trying to make a decision about whether to switch from Dino to synthetic. I have a 1990 C4with 90,000 miles. I have searched these posts to find some answers regarding leaks with the synth. I like the idea that it is slippery, but fear the leaks. Should I continue with Dino, and change more frequently, or should I switch over?
I drive aout 5,000 mile annually. Also, the only Mobil 1 that I can find at a reasonable price here is 10W30. I live in a warm climate and it can also be used in my Volvo. Any advice would be appreciated.

John Turk

Adrian

The choice of oils depends greatly on your local environment. Dino or synthetic. Well that is something else. Only US versions of the 964 were delivered with Dino oil. I have no idea why. ROWs were delivered with Synthetic. Shell. I run 5W 30 all season synthetic. The new oil from Mobil is OW 40. This is not recommended, certainly here in Europe for older engines. This is a tad thin.
If you decide on Dino oil you have to do oil changes every 3000 miles. Running a good synthetic you can expand this to 12500 miles for normal road use,
Ciao,
Adrian
911C4

Christer

MY Porsche Specialist uses a Castrol 15-40W in mine, after asking what kind of driving I did. I think he meant to put Mobil 1 in if I only did short trips.

I guess viscosity is more important than the make...?

lehmkuhler

Thank you very much for the feedback. I enjoy the forum, and I hope to be able to one day make a contribution instead of just asking questions. On a final note, would any of you consider it to be a mistake to add a different type of oil between now and when I get the next oil change?
Also, what does Dino mean?

Thanks,
Monte

samk

Autometrics of Charleston, SC. just ran th 24 Hours of Daytona on Schaffers Syn (993) with little or no wear on the bearings after tear down. I have been running it for 6 years and changing it every 6K miles. It gets dirty just as fast as non-syn. oil.
It feels like it adds about 20 HP. to my engine.
Hope this helps. Sam

Adrian

Dear Monte,
Dino stands for Dinosaur. You know what the oil started as.
I am personally not a fan of mixing oils. It "can" lead to problems. We do not do it on our aircraft engines which are dry sumped so I apply the same principles to my Porsche engine. In an emergency you may not have a choice but do an oil change to do the job properly.
For the record I change my oil every 20000km or 12500 miles. My current oil consumption is 1 litre per 15,000km.
Ciao,
Adrian
911C4

lehmkuhler

Thanks for your help everyone.

Monte

Paul Hewitt

I use Castrol GTX 20-50 in my 90 C2 daily driver. I drive about 40 to 50 miles a day in NC. This was recommended by my mechanic.