Ultimate Motor Oil Thread or Why we hate CJ4/SM oils

[db_cooper]

I'd use at least the weight oil that was recommended at the time the car was sold, that would be 20w -50 through the end of '89 811 production

I'm not quarreling and yes, 20w50 is recommended for use between 15*F outside ambient air temperature and above, off the scale at 110*F

15W40 and 15w50 are recommended from 5*F and off the scale at the top too and is interchangeable with 20w50 at high temperatures.

From the owners 1980's 3.2 manual.

When it gets cold outside, I really don't want 20w50 in the crankcase. Ever leave a bottle of 20w50 outside when it gets below freezing? It pours like molasses. Can't imagine what it would be like at 15*.

I would quarrel with the engineer who specified that requirement.

On topic..yes we need ZDDP. No it is not enough ZDDP quantity in Mobil1 0w40.

[Bill Verburg]

Originally Posted by db_cooper

I'd use at least the weight oil that was recommended at the time the car was sold, that would be 20w -50 through the end of '89 811 production

I'm not quarreling and yes, 20w50 is recommended for use between 15*F outside ambient air temperature and above, off the scale at 110*F

15W40 and 15w50 are recommended from 5*F and off the scale at the top too and is interchangeable with 20w50 at high temperatures.

From the owners 1980's 3.2 manual.

When it gets cold outside, I really don't want 20w50 in the crankcase. Ever leave a bottle of 20w50 outside when it gets below freezing? It pours like molasses. Can't imagine what it would be like at 15*.

I would quarrel with the engineer who specified that requirement.

On topic..yes we need ZDDP. No it is not enough ZDDP quantity in Mobil1 0w40.

Of course, If you drive your car when it's that cold then adjust the oil accordingly, many if not most of us don't

[richardlw]

Originally Posted by db_cooper

I'd use at least the weight oil that was recommended at the time the car was sold, that would be 20w -50 through the end of '89 811 production

I'm not quarreling and yes, 20w50 is recommended for use between 15*F outside ambient air temperature and above, off the scale at 110*F

15W40 and 15w50 are recommended from 5*F and off the scale at the top too and is interchangeable with 20w50 at high temperatures.

From the owners 1980's 3.2 manual.

When it gets cold outside, I really don't want 20w50 in the crankcase. Ever leave a bottle of 20w50 outside when it gets below freezing? It pours like molasses. Can't imagine what it would be like at 15*.

I would quarrel with the engineer who specified that requirement.

On topic..yes we need ZDDP. No it is not enough ZDDP quantity in Mobil1 0w40.

All books, manuals, etc. need to be read in relation to what was known and available at the time of printing. I once worked for a company that tried to solve that problem. Every 6 months we sent out thousands of little stickers to registered owners with instructions as to which page to paste the corrections. On field visits I saw about 30% were applied.

Before good synthetic technology and group II base oils, getting a 30 point spread in a multigrade (20W-50) meant a lot of polymers, and little was know as to which polymers could resist shear. So if your engine design was for a 50 at operating temperature, you had to spec 20W-50 and hope for the best. Some brands used the expensive polymers, others not. Group II oils didn't become common place until the 90's or later. Once polymer technology improved and group II oils became more standard, you could be more assured of less shear, but sticking with brands that concentrate on quality instead of price. (group II uses less polymers) With the design of good, affordable, synthetics, you can have low temp protection and high temp protection.

I've measured a 4 second difference in oil to bearings between 15W-40 and 20W-50 at 25C. Not something worth playing with.

[db_cooper]

My point being the 3.2 911 engine was really engineered with a 40w in mind rather than a 50w.

The owner's manual even has the ranges for single grade oils. There is no range for straight 50w. Straight 40w was recommended between 70*F outside ambient air temperature and off the scale at +110.

There is a paragraph on "fuel efficient oils" and talks about synthetic or hydrocrack oils. The range is -10*F to max 110*F for 10w40 or 10w30.

I would not completely agree about 10w30 there too.

I use 5w40 synthetic HDEO year round. Big additive package and ZDDP.

I think 20w50 is too much unless you are racing in the heat of summer.

[Bill Verburg]

Originally Posted by db_cooper

My point being the 3.2 911 engine was really engineered with a 40w in mind rather than a 50w.

The owner's manual even has the ranges for single grade oils. There is no range for straight 50w. Straight 40w was recommended between 70*F outside ambient air temperature and off the scale at +110.

There is a paragraph on "fuel efficient oils" and talks about synthetic or hydrocrack oils. The range is -10*F to max 110*F for 10w40 or 10w30.

I would not completely agree about 10w30 there too.

I use 5w40 synthetic HDEO year round. Big additive package and ZDDP.

I think 20w50 is too much unless you are racing in the heat of summer.

M1 15w-50 will be fine for the vast majority of us that don't drive our cars through an Alaskan winter. I'm sure there are lots of folks that use lighter oils, whatever floats your boat.

[Nick Triesch]

My 85 Carrera just turned 140,000 on the clock. It better well go another 140,000 or I will be ticked off! That darn oil better do it's dang job! BTW, I notice that here in SO CAL, even with our great climate (72 year round average) you just do not see 1985 cars around. They are all long ago flattened. But I sure do see a lot of older, classic P-cars!

[Jimmysidecarr]

Good afternoon.

I just wanted to pass on some information related to this thread topic since we (Royal Purple) recently reformulated our SAE/API street oils and although both old and new formula are still often able to be found, a little checking of the back label for the API license will be worth doing.

Due to the reduction in anti wear from the API-SM cap of 800ppm phosphorus our SAE/API-SM and SN street oils are no longer the best choice for flat tappet performance engines with lifts above .500". We do not recommend our SAE/API-SN 20W-50 (part #01250, quart bottle) or SAE/API-SN 10W-40 (part #01140, quart bottle) for those applications any longer.

There are still multiple Royal Purple oils available that are appropriate and though exact levels are proprietary, typical zinc and phosphorus are in excess of 1200ppm.

Those appropriate and recommended oils for air cooled Porsche engines are as follows.
If you can still find the old formula Royal Purple API-SL SAE 10w-40 and API-SJ 20W-50 those are fine and though they are not your best choice(from us) they will still be better than many other oils on the shelves these days.

As you go down the list the level of performance and protection increases and the price will too.

Royal Purple HPS 10W-40 (part #31140, quart bottle)(new)
Royal Purple HPS 20W-50 (part #31250, quart bottle)(new)

Royal Purple Max Cycle 10W-40 (part #01315, quart bottle)(unchanged)
Royal Purple Max Cycle 20W-50 (part #01315, quart bottle)(unchanged)

Royal Purple XPR 10W-40 (part #01041, quart bottle)(unchanged)
Royal Purple XPR 20W-50 (part #01051, quart bottle)(unchanged)

If you have any questions please feel free to contact me at the Royal Purple technical support department 8-5 mon-fri @ 888-382-6300

or via email : jmorrissey@royalpurple.com
or the general tech department email: rpautotech@royalpurple.com

Thank you for allowing me to share this important update.

Jim Morrissey
Technical Services
Royal Purple, Inc.

[HarryD]

Jimmy,

Thanks for the update. One question, will the labelling on the front of the bottle help us make the right choice or will we need to delve into the fine print.

[cnavarro]

Originally Posted by Jimmysidecarr

Good afternoon.

I just wanted to pass on some information related to this thread topic since we (Royal Purple) recently reformulated our SAE/API street oils and although both old and new formula are still often able to be found, a little checking of the back label for the API license will be worth doing.

Due to the reduction in anti wear from the API-SM cap of 800ppm phosphorus our SAE/API-SM and SN street oils are no longer the best choice for flat tappet performance engines with lifts above .500". We do not recommend our SAE/API-SN 20W-50 (part #01250, quart bottle) or SAE/API-SN 10W-40 (part #01140, quart bottle) for those applications any longer.

There are still multiple Royal Purple oils available that are appropriate and though exact levels are proprietary, typical zinc and phosphorus are in excess of 1200ppm.

Those appropriate and recommended oils for air cooled Porsche engines are as follows.
If you can still find the old formula Royal Purple API-SL SAE 10w-40 and API-SJ 20W-50 those are fine and though they are not your best choice they will still be better than many other oils on the shelves these days.

As you go down the list the level of performance and protection increases and the price will too.

Royal Purple HPS 10W-40 (part #31140, quart bottle)(new)
Royal Purple HPS 20W-50 (part #31250, quart bottle)(new)

Royal Purple Max Cycle 10W-40 (part #01315, quart bottle)(unchanged)
Royal Purple Max Cycle 20W-50 (part #01315, quart bottle)(unchanged)

Royal Purple XPR 10W-40 (part #01041, quart bottle)(unchanged)
Royal Purple XPR 20W-50 (part #01051, quart bottle)(unchanged)

If you have any questions please feel free to contact me at the Royal Purple technical support department 8-5 mon-fri @ 888-382-6300

or via email : jmorrissey@royalpurple.com
or the general tech department email: rpautotech@royalpurple.com

Thank you for allowing me to share this important update.

Jim Morrissey
Technical Services
Royal Purple, Inc.

Yet another reason to safely say that motorcycle oils are a good backup choice with the usual suspects (Brad Penn, Swepco, etc.) are not readily available.

[mystro]

The RP XPR 10w40 is my first choice in oil.

[911pcars]

Goes to show that oils can be reformulated at will. What is contained last week can be added or removed the following week.

Sherwood

[timchar]

Is it true that Brad Penn is not to be used on cars with catalytic converters? Tim

[Reiver]

Originally Posted by timchar

Is it true that Brad Penn is not to be used on cars with catalytic converters? Tim

Higher zddp that protects flat tap motors, like our air cooled P's, has a neg effect (can plug up) cats...that is why it was removed or lowered in most 'modern' oils and why we are having this whole discussion.
I don't know if the P's cat is adversely affected by it or what the time line may be. I've removed mine so no idea.

[dshepp806]

Originally Posted by richardlw

All books, manuals, etc. need to be read in relation to what was known and available at the time of printing. I once worked for a company that tried to solve that problem. Every 6 months we sent out thousands of little stickers to registered owners with instructions as to which page to paste the corrections. On field visits I saw about 30% were applied.

Before good synthetic technology and group II base oils, getting a 30 point spread in a multigrade (20W-50) meant a lot of polymers, and little was know as to which polymers could resist shear. So if your engine design was for a 50 at operating temperature, you had to spec 20W-50 and hope for the best. Some brands used the expensive polymers, others not. Group II oils didn't become common place until the 90's or later. Once polymer technology improved and group II oils became more standard, you could be more assured of less shear, but sticking with brands that concentrate on quality instead of price. (group II uses less polymers) With the design of good, affordable, synthetics, you can have low temp protection and high temp protection.

I've measured a 4 second difference in oil to bearings between 15W-40 and 20W-50 at 25C. Not something worth playing with.

How was this measured? 4 seconds is seemingly forever,.. wondering what it is at 30 degrees?

Best!

Doyle

[timchar]

My car has a cat, I'm trying to find out what is the best oil for the motor that wont damage the cat? I have read some of this thread but, 4 years worth will take me forever to possibly find my answer. Thanks if anyone can chime in... . Tim

[HarryD]

Originally Posted by timchar

My car has a cat, I'm trying to find out what is the best oil for the motor that wont damage the cat? I have read some of this thread but, 4 years worth will take me forever to possibly find my answer. Thanks if anyone can chime in... . Tim

Tim:

What year is your car?

Generally speaking, the downside of using high ZDDP oil is a POSSIBLE early demise of your Cat. But here some food for thought:

Cats have been in cars since the '70's;
There is no reason not to expect a Cat to last 75-100k+ miles regardless of the oil selected;
Until the mid 90's, most all motor oils contained high levels of ZDDP;
The cost to replace a dead cat is around $2k;
The cost to rebuild an air cooled engine is $10-20k;
High ZDDP will kill your cat prematurely;
Low ZDDP will kill your flat tappet engine prematurely.

Based on these facts, this is how I see it.

ZDDP has not been an issue for cat life until the mid 90's. The cost to rebuild an engine is an order of magnitude higher than replacing a cat.

If I had to choose, I would gladly kill the cat to preserve my engine.

What about you?

[timchar]

Harry, its an 86, I just purchased two months ago. It has 180 k motor rebuilt 25 k ago. I agree with you, better to cook the cat instead of the motor. It was about 10 k to rebuild motor. Thank you for breaking this 5 year thread down to a few paragraph answer that makes perfect sense. I can order my oil now. Tim

[HarryD]

Tim:

Glad to help.

[RWebb]

one thing to add to Harry's comments is that EPA is concerned about long term functionality of the catalytic converter- 50,000 or 100,000 miles

I would use an oil with ZDDP and figure that the car would continue to meet its emissions specs. for many decades at the miles/year that most drive.

[richardlw]

Originally Posted by dshepp806

How was this measured? 4 seconds is seemingly forever,.. wondering what it is at 30 degrees?

Best!

Doyle

It was seemingly forever. First just an observed shocking difference that it took 6 seconds for the light to go off (when I knew it always went off in 2 seconds). So then I looked at my watch, about 4 starts a day for 4 days. That's when I changed back to 15W-40 and total time went back to 2 seconds. Could it have been 6.5 or 5.5, sure. I was not intended to be a study. Just turned out to be.