Which Oil???

[rgunson]

I have a 1971 2.2S with a completely rebuilt engine that I am running in using 15W-40 Shell Oil, although I think the question relates to all early 911s

What is the 'best' oil to use?

My mechanic understands that the fully synthetic oils with their associated lower viscosity are niot suitable for the early engines. While I understand this from a 'oil might leak out in strange places' perspective (although surely the risk is minimal on a fresh rebuild), I do not understand it from an engineering perspective. i.e. will the oil pressure drop/other abnormal effect due to unsuitable oil pump etc - i don't know I am just trying to think of possible reasons as I don't really accept this point of view

On the otherhand I know a guy who used to build kart engines for racing & feels that I should be using 10W

Finally, still others think you used the most advanced oil you can get your hands on (a fully synthetic Mobil 1/Shell Helix/etc)

I note on the Mobil 1 website there is a facility whereby you can search for the correct oil for you vehicle. For all pre-1980 911s it recommends a version of Mobile 1 that is targeted at high load applications (incl trucks, etc), which incidentially is a 10W version of Mobil 1.

I am well aware that opinions on this subject a diverse, but would still like to post this question and see what comes back - I can't find a post that addresses this directly, so please correct me if it has already been directly addressed in some detail elsewhere

Thanks.

[B D]

Personally I believe any oil with a high zinc content is best. The zinc is what protects parts during metal to metal contact (mainly startup). Valvoline Racing has the highest content I am aware of. Valvoline Racing, Kendall, Castrol, and Chevron have high zinc content and are what many run in their cars. I run Chevron 20-50 it has the high zinc content it's cheap (under $20 a case) and is available almost everywhere. Check the Pelican Parts BBS there have been several threads on oil over there, but no real conclusion.

FAQ and Charts on oil: http://www.atis.net/oil_faq.html

[72targa]

First, some basics...

1) 10W-30, 15W-40, etc. are multigrade oils. This means that at low temperatures (at start-up), they function like the lower number (essentially, the smaller the number, the less viscous the oil at a given temperature). And then at higher temperatures (operating temperature), the oil functions like the higher number. Thus, at start-up, your 15W-40 oil functions as a relatively "light" SAE 15W oil and when the engine warms up, your oil functions like a relatively viscous SAE 40 oil. This multigrade variation is accomplished by using polymers called viscosity index improvers. All multigrade oils use them.

2) In the US, oils like SAE 5W-20, 5W-30 and 10W-30 are the primary automotive recommendations with 5W-30 and 10W-30 as the main players and 5W-20 growing. SAE 20W-50 and 10W-40, as well as single grade oils (SAE 30 and 40) are still made but are not recommended by any auto OEMs. Castrol, you may remember, was big on SAE 20W-50 but the ILSAC requirements pushed OEM recommendations to oils with either 5W or 10W as the first number. On those oils, you will see the "Starburst" on the front of the bottle. However, you won't see this on SAE 10W-40 as OEMs stopped recommending this oil some time ago due to deposits found in engine tests on this grade.

In the UK, most of the same grades are available, but of course, there are differences. Whereas in the US, SAE 15W-40 is primarily directed at heavy duty, on-highway trucks, in the UK, 15W-40 is a bit more universal.

3) The significance of the viscosity grade is the amount of oil film it provides to the moving parts at operating temperature. When the engine is cold, you don't need much. When it's hot, you need more. If, for instance, you have an engine that runs very hot, you could need a very viscous oil so as to maintain a proper oil film. That's one of the reasons why drag racers are known to use SAE 50 or 60 oils (another reason is fuel dilution, but we won't get into that). For your 911, a 30 or 40 weight oil (remember, the second number of a multigrade oil) will be just fine at operating temperatures.

4) The word synthetic is a challenging one now for sure. You used the term "fully synthetic". I assume you mean "made from PAO (polyalfaolefins)" as historically that was what it meant. PAO base oils are quite capable at finding places to leak from relative to their petroleum based counterparts. On a new or reebuilt engine where everything is "tight", that should not be a concern. The primary reason for the PAO oil's ability to find leaks is due to its affect on seals. Petroleum oils tend to cause seals to swell. PAO's tend to cause them to shrink (ever so slightly). Thus, leaks can occur when switching from petroleum based oils to PAO based oils.

Currently, though, very few 'synthetic' oils are made from PAO. Most are made with "Group III" oil that is a highly refined petroleum oil. This oil delivers the same high and low temperature properties as PAO and is considered to be created by a synthetic process of rearranging molecules and has thus earned the right (literally and in the court of law) to be called 'synthetic'. Mobil 1, for instance, is still PAO-based, though. Read the label.

5) Zinc is certainly an important component. It represents the Z in ZDDP (zinc dialkyl dithiophosphate). This is the primary antiwear additive found in many oils. Suffice it to say, enormous amounts of engine tests have shown the proper amount of ZDDP to put in an oil. This amount has to be balanced with the amount of phosphorous in the oil (another part of ZDDP). Currently, emissions systems do not allow for more than 300 ppm phosphorous. Thus, you are limited in the amount of ZDDP in an engine oil.

6) One thing to consider is what is the oil primarily built for. Heavy duty truck oils tend to have much more dispersants/detergents that those built for passenger cars (due to the type of fuel and length of service). Thus, they will have a greater capability to keep the innards of an engine clean. However, most are not readily available in automotive SAE grades (5W-30, for instance) but are instead only available in typical "Class 8" truck grades (such as 15W-40). So, it's a tradeoff...you can't meet an auto warranty requirement when using them but they can function well in an automotive application. Most heavy duty truck oils will have both a diesel rating (API CI-4) and gasoline rating (API SL)

Also, some of the European (especially Mercedes Benz) can be quite severe so if an oil meets MB p229.31, for instance, that's nothing to sneeze at. Likewise, there are significant Japanese (JASO) and European (ACEA) specs as well.

*****************

As you might be able to tell, I could go on and on with this subject. So what's all of this mean for our old cars? In simplest terms, no one of is dealing with any warranty requirements. We can pick and choose what we want to use. In my experience, since my car has never been under warranty during my ownership, I went with what I thought would be the best of both worlds. I use an SAE 15W-40 motor oil in my car. It has the automotive API SL rating mentioned above, slightly higher average oil vis than specified by the automotive OEMs (I'm old school) and it has the incredible cleaning abilities of a heavy duty engine oil. Combine that with regular oil changes (every 2000-3000 miles...OIL IS CHEAP), and I think I'm in good shape.

[Chuck Miller]

rgunson,

Check this out...

http://d240157.u39.zeonhost.com/foru...ht=kendall+oil

Cheers,

[rgunson]

ok, so if i u/stand it correctly;

1. there is no real downside from moving to fully synthetic, other than the possibility of a leak or 2
2. many upsides to using a full synthetic
3. zinc is good, but not too much (refering to link on oils provided - excessive zinc content can form deposits, etc)
4. the numeric differential between the upper and lower ratings should be a narrow as possible, and in all cases less than 30 (which raises questions as to why oils like 15W/50 are still on the market?!)

I understand the basics of the rating codes, i.e. the 'W' number represents the viscosity in lower temperatures - the lower the number the better for cold starts when the oil is at its most viscous.

However, I am guessing that the oil in an air cooled 911 reaches a much higher temp than in a water cooled vehicle driven in a similar manner in the same weather conditions.

This raises the question, is there a minimum value for the second rating number that we should not go below for early 911s, as I understand this represents how well the oil handles at maximum operating temps (i.e. resistance to breaking down & losing its lubricating properties at high operating temps). The higher the value the better the oil handles the maximum operating temp is my understanding.

Any ideas?

[rgunson]

Hi there 72 Targa

This is the oil I had in mind, but does it fall foul of you comments in point 2 above about 'wide-range' multi-grade oils i.e. 20W/50 and wider?

http://www.mobiloil.com/USA-English/...SUV_5W-40.aspx

Thanks



Reiss.

[72targa]

From rgunson:

1. there is no real downside from moving to fully synthetic, other than the possibility of a leak or 2 - True
2. many upsides to using a full synthetic - Only if you really need it (very high temps or very low temps)
3. zinc is good, but not too much (refering to link on oils provided - excessive zinc content can form deposits, etc) - Specifically, zinc does not cause deposits. The phosphorous in ZDDP can cause a catalytic converter to fail if the phosphorous is >300 ppm in the oil. As our cars have no catalytic converters (yeah!), this point is moot. However, current oils are blended with catalytic converters in mind so you don't really have a choice.
4. the numeric differential between the upper and lower ratings should be a narrow as possible, and in all cases less than 30 (which raises questions as to why oils like 15W/50 are still on the market?!) - Good question. The answer is "not really". Whereas the auto OEMs have found that 10W-30 is good but 10W-40 is bad (and hence they do not recommend it), plenty of customers still want 10W-40 and so the oil companies still make it. Depends on who you believe. I tend to believe the OEMs and the millions of $$ of testing that has gone into their recommendations. Specifically, the greater the numeric differential between the upper and lower ratings, the wider the temperature range that the oil can properly function in.

***************************************
Also from rgunson:

I understand the basics of the rating codes, i.e. the 'W' number represents the viscosity in lower temperatures - the lower the number the better for cold starts when the oil is at its most viscous. - Yes, that's why you'll also see some newer oils with 0W (yes, zero) for the first number. From the OEMs standpoint, this number is also key to meeting CAFE standards (i.e. - an SAE 0W-20 would offer the least resistance and thus the best gas mileage).

However, I am guessing that the oil in an air cooled 911 reaches a much higher temp than in a water cooled vehicle driven in a similar manner in the same weather conditions. - I tend to agree with that. As Chuck Miller pointed out, a recent survey showed most users on this board use SAE 20W-50. An SAE 50 oil give the thickest oil film at our average engine's operating temperature. I personally have raced for some time quite successfully using SAE 15W-40. I would most likely NEVER put an SAE 5W-20 oil in my car.

This raises the question, is there a minimum value for the second rating number that we should not go below for early 911s, as I understand this represents how well the oil handles at maximum operating temps (i.e. resistance to breaking down & losing its lubricating properties at high operating temps). The higher the value the better the oil handles the maximum operating temp is my understanding. - See above.

[72targa]

Hi there 72 Targa

This is the oil I had in mind, but does it fall foul of you comments in point 2 above about 'wide-range' multi-grade oils i.e. 20W/50 and wider?

http://www.mobiloil.com/USA-English/...SUV_5W-40.aspx

Thanks

Reiss.

Another excellent question. I would expect it to work well. The reason why this product has such a wide range is that it is based on PAO. It does not need VI improvers (or as much) to get the cold-hot vis range you see. PAO's exhibit this viscosity range "naturally".

[boxster03]

seems like a lot of the old school Porsche mechanics are staying away from the synths for our old iron and pushing 20/50 at least here in So.Cal. Maybe they would move to the 10/40 in colder climes. if you are going to change your oil every 2-3k syn oil might be a bit expensive, but then again it does have advantages for longer term storage. my 2cents worth..

[rgunson]

Thank-you to everyone who replied. As Boxster03 mentions they seem to be pushing the heavier oil for the older cars (in the UK too). I raised this topic because I couldn't understand what the mechanical justification would be if the engine was a complete rebuild. This is especially so in my case as I have replaced all 6(ouch!) pistons & sleeves & rings. I discovered that Porsche now only sell Nikasil pistons & sleeves (yes, incl the 2.0, 2.2, 2.4, etc). This suggests to me that a modern oil must be the best solution as they are a very snug fit. I had also been told that the early oil pumps dont pump the thinner oils as well as the heavier oils, etc - all of which looks to be unfounded on fact. The way I see it the lower the 'winter' number the easier it is for the pump to send it round a cold engine in those first critical seconds of metal-metal contact on start-up. I also agree with targa72 in his comments about the high temp number, and would never use an oil with a '20' rating - unless i lived in the arctic circle perhaps! I also think the if you take a product from a major producer like Exxon/Mobil, Shell, or BP/Castrol you probably can't go too far wrong. Please note that all my conclusions relate to a rebuilt engine - I can quite understand that putting a synthetic oil into well-worn engine that has been running on a heavier mineral oil is likely to cause leaks, and possible dislodgement of sediments that may clog/block oilways. I have decided to go with Shell Helix 5W/40, although I would be just as happy with the equivalent Mobil product I posted earlier - it is just that my mechanic only uses Shell oil (and has done for 30+years). I will let you know how I get on. Again many thanks, Reiss.