fbfisher

Mobil 1 0W-40 is hard to find on the shelf at gas stations and auto parts stores. There are times when oil should be added but only 15W-50 is available.

Would you add one or two quarts of 15W-50 to a crankcase with 0W-40 already in it? P-Car dealer mechanic says "no problem."

What do you say?

914und993

There should not be a problem. Your resulting oil viscosity will be pretty close to the weighted arithmetic average of the viscosities of each oil.

Chip

JimBob Jumpback

Yo bubba,

dont yall be doin dat cuz it bein awl messeded up. wen yall mixn da erl, yall gotz ta added da nummernuts togedder. so 15w plus naughtW is 16W and 50 pluss 40 is pert neer 97 so yaall be gittn 16W-97 erl an dat no bein no gooder fer yur moter.

yur fren
JimBob

fbfisher

Thanks JimBob, you have just redefined the meaning of "new math."

So, one "yes", one "no." Anyone care to break the tie?

ca993twin

As much as I respect and admire JimBob's math and tortured use of the English language, Chip and your P-car mechanic have it right. In Los Angeles, however, you should be using 15-50W all year round. At least, that's what I've been told by many knowledgable folks. JimBob... what's your take on that?

fbfisher

Fartus - this oil weight thing has me spinning. Techs at Auto Gallery in Woodland Hills only want to put 0W-40 at oil change.

As you know, road temps can often exceed over 110F in the summer, and though this has been a cool spring, air temps in the 70-80 range for most of the year are not uncommon.

As the car is a daily driver I need the oil to be helping as much as possible. What to do?

914und993

Choice of oil weight is controlled in part by engine designers. Air cooled engines, because of their wider range of operating temperatures have looser tolerances and require higher viscosity oils.

Lower viscosity oil is actually better for an engine - i.e. reduced frictional losses and reduced wear - up until that point where because of high temperatures and loads the film breaks down and results in metal to metal contact, which of course is very bad.

Higher viscosity oils will resist film breakdown under high temperature/load conditions better than low viscosity oils, but they may actually reduce engine output, and under non-severe conditions cause more wear to the engine.

Thus we see Porschephiles who track their cars using 15W-50 instead of the currently recommended 0W-40 synthetics because they want that extra bit of insurance against catastrophe. Is it necessary? Heck if I know. Porsche seems to think 0W-40 is fine for 150 mph on the Autobahn, but if I were running at the track in August in Oklahoma, I would be using 15W-50. For street use, 0W-40 is fine for me.

Chip

DJF1

Porsche changed their recomendation lately. That means that while our 993's were produced the recomendation was for 15-50. There have been many threads as to which oil to use, on some of them I took the time to write in length my story about 0-40 dealer oil change and what condition this oil was after 2k miles on my car.
To sum up my observations in hot climates, when tracking the car or daily high volume traffic my 30+ year experienced mechanic refuses to put anything but 15-50 and so do I. If I was at winter temps of 32 or so and below I would change to 0-40 for these months only.
Porsche may need to sell more spare parts for our aging bulletproof cars, I do not want to pay for them.

Flying Finn

I'm with Danny & others, in your temps, stick with that 15w-50. Simple as that.

914und993

I remember Danny's post on his experience with 0W-40. It certainly would have been interesting to actually have a formal oil analysis on that sample to see exactly what was going on - high temperature damage, shear-induced viscosity breakdown, fuel contamination, or what. I guess only the nose knows....

But there is plenty of anecdotal experience around here, you'll have to read it and come to your own conclusions.

Chip

bet

I just got back from the Visit 3.0 in bowling green where we held a round table discussion/question and answer session with many of the PCA national tech advisors (including Bruce Anderson) and very some very well respected tuners. I posed the question what is the best oil for the 993 and asked them to comment on the oil change intervals.

Short answer: 0w-40 is much better for the lifters, and that unless you vehicle is seeing lots of track time and/or extreme heat that is probably the best choice. Neither is bad.

The most important thing mentioned was that the oil change intervals have come about from environmental pressures on "total pollution from a car" and that in reality more frequent oil changes can not be stressed enough.

They all recommended every 3000-5000 (max 7500) for oil change frequency. The more the oil temp is cycled (very hot/cool/very hot) the more frequent the oil change. It didn't matter what oil (0w40 or 15w50) you should still change it frequently. It was a fairly detailed talk and more was said but that was the short answer.

fbfisher

This is a great thread, thanks to all for your contributions. Since the topic has come up, what would you define as "extreme temps" in terms of engine operating temp. My oil temp gauge can go from the third mark (about 7:30) to about the 9:30 position, higher on hot days in traffic.

By the way, my engine tray has been removed and I didn't notice much change.

Ray Calvo

Personally, I gotta go along with Brian and his experts. Ages ago (pre or early synthetic) , heavy oil was needed to avoid breakup at high temperatures. This isn't the case anymore; light synthetics can take the higher temperatures that Dino and early synthetics couldn't. So, now that I can get 0W40, I will be using it.

My oil temp gauge rarely goes higher than about the 9:30 position.

The engine undertray supposedly had a bigger difference on the old 964 than the 993, but to me still looks like a air block so it stays off. By the way, this undertray started back about '86-'87 as a sound shield; now Porsche is trying to convince you it's an aerodynamic device so you don't take it off.

Edward

I fully understand the virtues of a thinner oil, but I'm still not convinced that the 0W is not merely Porsche's concession to the wasser boxer crowd. I was speaking to someone "in the know" some time ago of Porscheland stuff, and when I brought up the Factory Recommendation to 0W, he went off about how too many 986/996 owners complained of noise, especially in colder climates and on those cars not driven daily. It's his belief that Porsche simply went to that recommendation to quell the noise (of the owners, that is).

Take this for what it is.....

Bottom line is one's own climate, driving habits, and track schedule should also be figured in the decision of which oil to use instead of just swapping weights "just cause the factory said so"...IMHO, of course.

Anyone want to volunteer their own hard-earned 993 as long-range testbed for 0W/40? Must be in warm weather, track reasonably often, and willing to suffer the conseqences...

Edward

Don Magee

It would be useful to run an oil analysis on 0w-40 and then 15w-50 run over the same number of miles and compare results. We might be surprised. The 0w-40 meets some stringent specs that the 15w-50 does not.