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Discussion Starter #1
First read:
http://www.lamborghini-talk.com/vbforum/showthread.php?t=778


Motor Oil 104
Part Four. It is not what we thought.

Now let us finish talking about the differences of mineral verses synthetic oils. I will compare the same weigh or grade of oils showing that the operating viscosities are the same whereas the startup viscosities vary:

Mineral oil:

Oil type...Thickness at 75 F... at 212 F...at 302 F

Straight 30..........250....................10..........3
10W-30...............100....................10..........3
0W-30..........There are none in this range......



Synthetic oil:

Oil type...Thickness at 75 F... at 212 F...at 302 F

Straight 30...........100...................10...........3
10W-30.................75...................10...........3
0W-30...................40...................10...........3

Since the synthetic oil thickens less on shutdown your startup will be easier and so will the stress on your engine. This is perhaps the best thing the synthetic class has over the mineral based oils.

People sometimes use a thicker oil to minimize gasket leaks. This seems obvious to me. Repair the gasket. Do not destroy your engine with an oil that is too thick for proper function.

Some people have said they use thicker oils because they only use their cars every 2, 3 or 4 weeks. They are afraid that thin oils will fall off the engine parts and result in a lack of lubrication at startup. Think about your lawn mower over the winter. I gets gummed up solid. The oil and fuel thicken over time resulting in engine failure. Anyway, oil on the surface of parts does not lubricate. It is the FLOW of oil between parts that lubricates. Thick, old, waxy oil can only be bad.

I have seen several car owner manuals that are now stating that oils do not need to be changed but every 7,500 miles or more. The same manual also states OR every 12 months, whichever occurs first. My feeling is that you can probably go 5,000 miles on the average (in a sports car) but you must change your oil in the spring time at a minimum, particularly up north. Oils form waxes in icy cold weather. There is a permanent thickening of the oil.

Some automotive manufacturers are backing down on oil change intervals to 5,000 miles or less and some advocate changing the oil at least every 6 months as well. I think this is because of the tendency for oils to thicken in very hot engines (not ambient conditions, just hot engines). Also because of thickening from the cold of winter and from sludge build up that cannot be filtered out.

I truly believe that oil is much better being too thin than too thick. Over the years we have been going to thinner and thinner oils despite hotter engines with turbos and the like. The tendency is that people figure they need a 40 weight oils but then use a 50 instead. Better thinking is that if you think you need a 40, use a 30 weight oil instead. I firmly believe this based on all I know about oils.

As it turns out synthetic oils do cling to parts better as they have higher film strength than mineral oils. Synthetics are thinner overall. They have greater slipperiness. Yet they stick better to engine parts. Again, this concept is the opposite of normal thinking.

The thickness of moving oil is measured in centiStokes or cS. Most engines want the oil viscosity to be around 10 cS at normal operating temperature. The really thick multigrade oils have a viscosity of 20 cS at operating temperature. One is not twice as thick as the other, it is only 10 cS thicker

continued....
 

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As we increase the heat from 212 F to 302 F the most commonly recommended oil thins from 10 cS to 3 cS. The thicker oil drops from 20 cS to 4 cS. Note that in a very hot engine the difference between the two oils is now only 1 - 2 cS. In other words they have about the same thickness. There is little advantage to a thicker based oil as a 20W-50 at very high temperatures. No, the 4 cS oil is not twice as thick as the 2 or 3 cS oil. This difference is almost insignificant.

There is a huge advantage of using the thinner, 10W-30 at startup where 90 percent of the engine wear occurs. At 75 F the thicker oil has a viscosity in the range of 250 cS while the thinner oil has a viscosity of 100 cS. The thicker stuff is 150 cS thicker. This is a very big difference. I am using the 20W-50 as my thicker oil example here.

People are always asking about adding things as Slick 50 into the oil tank. Do not do this. The oil companies and engine manufacturers work together very hard to give you the product you need. Engines are running hotter, longer with more BHP from less CID. Smaller, more efficient engines are getting us more MPG and yet better acceleration. These engines last longer and are more reliable.

Part of that reason is the nature of the lubricants. There is a lot of competition to get us the best working motor oil. Independent additives cannot make the oil better and in many cases makes things worse. There have been engine failures as a result of adding some of these aftermarket additives to motor oil.

Motor oil that is labeled for RACING ONLY is not usable for every day driving. Often these have more additives that are toxic to your catalytic converters and the environment. These oils generally do not have detergents. These are very important for your engine unless you plan on taking it apart every few weeks and cleaning every single surface. The oils do not meet the API / SAE requirements for ratings as SJ, SL or now SM.

You do not need to use the exact oil type and brand that your car manual tells you to use. Oils are pretty general. They are not that different. Ferrari is married to Shell. If you call them up and ask to use Valvoline instead they will tell you that they have not tested that brand in their cars. They only tested the engine with Shell oils. They cannot comment on the performance of other oils in their engines. This is a fair statement. The reality is that the Shell and Valvoline oils of the same specification (viscosity, API and SAE ratings, synthetic or not) are very similar. ( I do have my bullet proof vest on ).

People often say that their old 1980 car manual says to use a specific Brand-X motor oil. They keep trying to locate these older oils. First, just about any oil brand that meets the original specifications will do. Second, all oils are much, much better now. They are all much better. One could say that synthetic oils are better than mineral oils but is is hard to say that one brand is that much better than any other. Personally, I do stick to the big names. It does not mean that small motor oil companies are not as good. They could be better for all I know.

Using an oil that is less thick at startup has other benefits. Let us compare a synthetic 10W-30 to a mineral based 10W-30. Both give you a viscosity of 10 cS at normal engine operating temperatures. They both thin to 3 cS at high temperatures. At 75 F tomorrow morning the story will be different. The startup viscosity of the synthetic will be 50 whereas the mineral based 10W-30 will be 75. Again, both are too thick at startup but the synthetic will cause less startup time period wear and tear. You will get a little better gas mileage too.

The synthetic lubricated engine will turn over easier. This has the effect of using less power from your starter motor. It will last longer. Your battery has less of a current draw. This will also last longer. The battery was discharged less during the start so the alternator will rob less power from your engine to recharge. The alternator lasts longer and you get a little better gas economy. The only downside of synthetic lubricants is the cost. They cost 2 or 3 times as much as mineral based oils. Never-the-less I use plain Pennzoil multigrade mineral based 5W-20 in my Ford Expedition. This oil is thin enough at startup to have many of the attributes I just mentioned.

aehaas
 

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Discussion Starter #3
Just to show some of the parameters that are tested in automotive gasoline engine oils I was able to get permission to reproduce the following from ASTM D 4485-03a. Most people do not get to see this data as the documents cost money and are of course copyrighted. With permission however:

From Table 2, S Engine Oil Categories
API SL CATEGORY (my note - most areas that give a measurement in mm = micrometers. It was difficult to transform the data into web friendly stuff.)

Engine Test Method.....Rated or Measured Parameter.....Primary Performance Criteria
Sequence IIIF.....Kinematic viscosity, % increase at 40°C, max.....275
...............Average piston skirt varnish rating, min....................9.0
...............Weighted piston deposit rating, min.........................4.0
...............Screened average cam-plus-lifter wear, mm, max.....20
...............Hot Stuck Rings....................none
...............Low temperature viscosity performance ..........report
Sequence IVA.....Cam wear average, mm, max........120
D 5302 B..........Cam wear average, mm, max...........127
(Sequence VE AD).....Cam wear max, mm, max ......380
D 6593
(Sequence VG) .....Average engine sludge rating, min.....7.8
...............Rocker arm cover sludge rating, min...............8.0
...............Average piston skirt varnish rating, min..........7.5
...............Average engine varnish rating, min.................8.9
...............Oil screen clogging, %, max...............20
...............Hot stuck Compression rings..........none
...............Cold stuck rings......................report
...............Oil screen debris, %...............report
...............Oil ring clogging, %.................report
D 6709 Bearing weight loss, mg, max..........26.4
(Sequence VIII) Shear stability..........footnote


Bench Test and Measured Parameter....................Performance Criteria

Test Method D 6557 (Ball Rust Test), average gray value, min.....100
Test Method D 5800 volatility loss, % max...................................15
Test Method D 6417 volatility loss at 371°C (700°F), % max.....10
D 6795 (EOFT), % flow reduction, max...............50
D 6794 (EOWTT), % flow reduction, max
..........With 0.6 % H2O..........50
..........With 1.0 % H2O..........50
..........With 2.0 % H2O..........50
..........With 3.0 % H2O..........50
Test Method D 4951 or D 5185, phosphorus % mass, max.....0.10
Test Method D 892 foaming tendency (Option A)
Sequence I, max, foaming/settling........10/0
Sequence II, max, foaming/settling........50/0
Sequence III, max, foaming/settling......10/0
Test Method D 6082 (optional blending required) static foam max, tendency/stability.....100/0
Test Method D 6922 homogeneity and miscibility..........footnote
High temperature deposits (TEOST MHT-4), deposit wt, mg, max.....45
Test Method D 5133 (Gelation Index), max ...............12

“Extracted, from ASTM D 4485-03 Standard Specification for Performance of Engine Oils, copyright ASTM International, 100 Barr Harbor Drive, Wets Conshohocken, PA 19428, USA.”

I was going to show more but it is a pain to make it work right. Anyway you can get an idea of how many things are tested. A lot of work goes into motor oils to make sure we get the best engine performance.

aehaas
 

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what about mixing oils?

This is all very useful information - please keep it coming!
What happens if you mix oils of slightly different weights? For example your car is filled with say 10 litres of 0-40 synthetic oil and when you check the oil level halfway through a long journey you notice that the level is low, but the only oil that the service station has is 10-40 or 10-30. So you add a litre of the 10-40.
Will this be OK? I'm assuming that the different oils will mix and that you end up with a kind of 5-40 type mix?
Regards
William
 

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Discussion Starter #5
Mixing oils.
The best choice is to plan ahead, bring a few cans with you in your travels, particularly if your oil is one that evaporates a lot.

If you are forced to add oil of a different type there are rules.

Use the same type and brand if you can. If you are using Mobil 1 then it is OK to mix different grades but use a close grade when possible. It is not a good idea to mix say 1/2 your oil tank with 0W-30 and 1/2 with 15W-50. This is a no-no.

If there is no Mobil 1 available then use mineral based oils next, preferably Mobil as first choice then any other name brand next.

The last choice is to mix a synthetic of another brand. They specifically say this should not be done.

Good question.

aehaas
 

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Dr Haas: Are you saying that it is okay to add some mineral based oil to your synthetic oil should you need to add??

If there is no Mobil 1 available then use mineral based oils next, preferably Mobil as first choice then any other name brand next
 

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Discussion Starter #7
Yes, if you need oil and cannot find the same synthetic then your next best choice is a can of mineral based oil.

The worst choice is adding some other brand of synthetic oil.

aehaas
 
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