Dave R.

Information supporting Adrian's philosophy of oil changing:

Hit this link to see an empirical test of Mobil 1. M1 lasted a long time - 18k, verified by oil analysis every 1k. Test of Amsoil is ongoing.

Note his observation (apparently consistent with FoMoCo observations) that the most engine wear per mile occurs during the first 3k on an oil change. In other words, engine wear *decreases* as oil ages (to a point). In particular see this page and note both the summary at the top, and the discussion of "Interpreting Wear Metals" at the bottom.



-Dave
'90 C2

garrett376

I wonder if the "study" findings would not directly apply to our "oil-cooled" cars - I think a 911 engine puts oil through the ringer a little harder than a water cooled engine. Might this change the interval slightly?

But, that was interesting, thanks!

Arjan B.

I made a few oil test in the lab myself at the TOTAL/FINA test lab [a French oil company]
In the test results [mobil 1 oil] was shown that the oil, which was running for about 20.000 kilometers, still was in good health. I only had a high % of copper n the oil back then, but that source was located later.

Mobil one is good oil.

We use it in the road cars [Opel Vectra/Vauxhall Vectra diesel for about 50000 kilometers without a oil change. No problem.

Arjan B.

Dave, send me your e-mail adress in a pm, and I will send you the test results from back then.

springer3

I don't think this type of test is informative, because it does not address number of cold starts, variation in trip time and city versus highway driving. These variables have a far greater effect on proper drain interval than mineral versus synthetic oil.

For exclusive highway use, 25,000 miles or more between changes is possible and has been documented. For short trips around town, and no highway runs to drive off condensed water and acids, even a 3000 mile interval is problematic.

Consider:

Every time the spark plugs fire, a small amount of combustion gas gets past the rings and into the crankcase. The gas is mostly CO2 and H20, but also contains NOX, unburned hydrocarbons, Sulphur, and other contaminants. When the hot gas contacts cold engine parts, the H2O condenses to water. Condensation stops only after the engine heats up enough to keep the water vapor from condensing. Then, the crankcase vent system handles it. Sulphur, NOX, and hydrocarbons combine with the water to form nitric, sulphuric, and other acids. Oil additives include buffers to neutralize the acids, but over time the buffers are depleted and the oil will become acidic (and start to attack metals). You need to change the oil to replace the additive package, and remove any other contaminants not removed by the filter.

If I had to chose between mineral oil with frequent changes, and synthetic oil with extended changes, I would pick the mineral option. Synthetics are better, but the benefit is debatable if the drain interval is extended.

Dave R.

Arjan, you have a pm!

Garrett,

it might, given higher oil temperatures especially on the track. On the other hand, our engines have nearly twice the quantity of oil than most. Mobil 1 also appears stable at higher temperatures so maybe our engines don't faze it as much as they would conventional dino oil.

What's really got me curious is the theory that changing the oil too often (e.g. every 3k miles instead of 10k) accelerates engine wear.


-Dave

Dave R.

Springer,

your points are well taken.

The tester does provide some information, e.g. "Its miles are split nearly 50/50 between city and highway, about 60 to 80 miles a day in spurts of 15 to 30 miles per trip. It tends to get around 20 mpg over the course of a month."

Regards,
-Dave

springer3

Go with what is in the owner's manual. That is based on research performed by professionals, and it can be trusted.

I give no credibility to a test run by amateurs or journalists on shoe string budgets. Too many critical variables are not measured or controlled. This is entertainment at best. The results cannot be trusted.

Dave R.

Springer, the factory owners manual that came with my '90 C2 recommends 15k miles between (mineral) oil changes.

How often do you change your oil?

springer3

Porsche 964: Six months (2000 - 3000 miles)
VW New Beetle (wife's): 5000 - 6,000 miles
Honda Passport (boat hauler): 7,000 miles
Boat (1/year, sadly only about 20 hours)
Mercedes 300 E (my beater) 5,000 miles
Kubota Tractor: 1/year (100 hours)
Lawn equipment 1/year

Using Mobile 1 10w-30 in all of them.

Bill Wagner

One of the things that I've noticed on fuel injected cars is that when I check the oil, it always smells like gasoline. It doesn't smell badly of gasoline, but enough (in my opinion) to make me wonder if a small amount of fuel isn't constantly leaking into the oil. Needless to say, over time this would (I assume) tend to dilute the oil.

I just breezed through the write up those guys had, and it appeared they were just using one car as a "sample". They probably should have done this on several different types of cars since factors that effect oil degradation (gas leaking in from injectors, temperature variations, normal operating temperature, etc.) will all play a factor and may vary considerably from car to car (especially with our air-cooled 911s that NEVER have a consistent running temperature).

Arjan B.

Dave R,

If you want, you may display the oil test results overhere. I can not upload them overhere because it's a pdf file.

JasonAndreas

Arjan,
Create a free Rennlist member site HERE and then you can upload any file type you want, upto 20 megabytes.

Arjan B.

Thanks for your help Jason. I have to find my way around there.

Arjan B.

Bill,

You're right, the smell of fuel is most of the time in every engine. If you start a engine, and let it run for 2 minutes, stop it and put you nose in the oil fill area, you will smell fuel.

The fuel comes with the engine ventilation system in the oil. Only if you use your car for a long drive, it will be hardly to notice. The HC's will burn then.