Once a year because if I did it by mileage, it probably would be at least every two years, which I think is too long time-wise. I'm no petroleum expert, but changing every 3,000 miles for synthetic seems extreme to me.

BTW isn't the factory recommendation every 15K miles - 15K, 30K, 45K, 60K, etc services with the 15K and 45K being only oil changes?

 

Here we go...

 

I find it funny, the factory stated 15kmi as normal. That was with 15 years or so oil. Oil has come a long way since then.

We are doing it at least once a year & with in 3-8kmi, that is at least HALF the recommended interval. With 2 oil filters, & 11+ qts of oil, it's fine. I had my oil tested last year on my C4 around 7000mi, & it was perfect. If the oil analysts comes out fine, the oil is fine to be in the car. What does surprise me is the fact that most people don't ever get the oil analyzed, it's the BEST way to see who the engine & systems are doing.

 

Exactly!

Under normal use conditions, changing the oil at 3K or 5K is a waste of money and resources. Even though the 993 has an air cooled engine, if the engine oil is in line temperature-wise, it won't break down any faster than on any other modern engine.

Furthermore, we have an incredible 11.5 liters of oil to share the workload in a tiny engine.


A co-worker has been running 25K kilometers (15.5K miles) between synthetic oil changes on the 2000 BMW 330Ci that he bought new. He has the oil analyzed in our labs and the according to them the oil is still good. Ten years later with almost 140K miles, his car is running just fine.

In Europe where cars tend to lead a harder life, where cars "cruise" at 125 MPH, the oil change intervals are 20K kms running on synthetic oil.

Mileage aside, I will change it once a year.

 

YIKES! A dreaded oil thread!!!

OK, I'm new to 993, but hardly new to oil threads or intense engine oil topics. My POV is that it depends upon use. Our 993 is a GT only type of car. Once the engine starts, it will be on for many miles plus we don't use the engine in a highly competitive manner. In fact, our usage would be classed as 'ultra light' by an oil guy because the oil never gets too hot but always remains hot enough to evaporate off the bad stuff.

Benz either does or used to have an oil sensor saying when the oil needs changing rather than the obsolete time or miles measure we're talking about here. My info is the general miles a Benz goes before it needs its oil changes, based on the oil sensor, is 18k miles. We should go longer if we aren't in competition or driving like we are.

In general use, we probably can easily go 15k miles between changes. Any more oil change benefits our senses more than it does the engine.

However, intense driving like on a track or daily driving where the oil doesn't reach temp - either changes the picture wholly.

 

A 993, by virtue of using 1 qt per 2K miles, changes half its own oil every 12K miles.

 

Once a year, just immediately prior to storing it for the winter. Mileage-wise it turns out to be only about 2000 - 2500 miles a year.

 

What causes oil to get bad after a few months in your car?

 

Where does one get oil anylized and what is the cost?

 

It doubt its a sensor analyzing any aspects of the oil chemistry. If its anything like the BMW system (based on my limited knowledge here) a computer analyzes the engines operating conditions to determine the oil change time.

I would be shocked if oil analysis after 5000 miles (on synthetic) didn't indicate that we are changing the oil well before it is required as far as viscosity goes. I can't say when a reduction in the wear additives occurs but an analysis could. The concern, valid or not at 5000k, is that high acid levels will hurt the engine while in storage thus the need for a pre-storage oil change. Again, for $150 I'll do the change in the fall whether it needs it or not.

 

http://www.blackstone-labs.com/

It's $25

 

I"m not against changing the oil, but I still contend it's due to us giving a gift to the cars / bikes we love rather than a need.

I have never heard that oil which is used lightly, like ours is (never short trips) has any significant acid level which can hurt an engine. Oil also doesn't get acid over time. That is, the idea of changing every X months no matter usage is, IMO, utterly silly. It MAY make sense in other cars, though.

Let's take a car used by a tubby housewife. She lives 4 blocks from the grocery store but uses her car to go there and back 3x week. Then there are a few other short trips she uses it for. After 6 months she's got 2k miles doing this but by now the oil is gone gone gone.

Now compare to our 993. I doubt the engine has been started w/o it going at least 50 miles. We haven't tracked the car so it's been used within the easy range of the engine's capacity. That's ultra light use where the oil gets hot enough to remove the water and acid from the last shutdown but never too hot to break it down.

As to the Benz tech, I"m completely ignorant. I would like to know it but also even if it analyzes engine use / conditions, I think it valid.

 

If you have one, could you post a PDF of your oil analysis so that some on here can see what they are about ?

 

I got some recently from Charles at LN (Staveley Services) -- no results yet
http://www.lnengineering.com/oiltesting.html

 

I looked at the sample PDF on their site and could not understand a thing without some reference point for my car or oil.