I have 160000 miles on my 1997 Marquis that has a c12 cat engine.  I have changed the oil regularly at about 15 to 18 thousand miles and only have to add a quart between changes.  I now am ready to change and am thinking about synthetic oil.  Do any of you folks use synthetic oil and if so what are your thoughts.  They would be appreciated.
David Fischer

Go to the http://catrvclub.org/tech_tidbits.htm CAT RV Club Tech Tidbits and there is a lot of information there. The CAT RV Forum on yahoo URL under links above has a lot of discussion on it also.

The CAT RV service representatives reccomends synthetic as long as it meets the standards specified by CAT.

I use either Amsoil or Mobil One on all of my modes of transportation other than the motor home.  I have never had an engine problem due to lubrication and that includes boats, snowmobiles, trucks and cars.  Firm believer in synthetics, will probably convert Beaver also.  Previous owner changed oil (Shell Rotella) every 5,000 miles and I change (Shell Rotella) before I head South every Winter which works out to be the same.   The biggest difference is much more expensive on a motor home vs. a car, but a motor home engine is much more expensive also.

I read a tear down report on a C12 engine used in an over the road truck that saw normal heavy duty service compared to our RVs. Cat bought the motor to look at wear tolerances at roughly 1.25 million miles using standard approved oil. Their conclusion was that the main bearings, rings, valve train stc. was still within tolerance and had several hundred thousand miles of life at the current wear rates before needing any work. My conclusion is good diesel approved oils like Rotella or Delo changed at rational intervals are just fine and given the wear rates with those oils we will never reach end of life of internal components. Save your money.

I think that only using Cat filters for oil and fuel is a far better choice than the rest of the market place. Cat put a lot of effort into fuel filter technology with very high capture rates at .5 miicrons. Their oil filters by design are highly efficient and have excellent seals and very heavy well designed metal interfaces.

If I had to guess what we could do to provide excellent life it would be, watch fluid levels, belts, idler pulleys (pull the belt and rotate them by hand to see if they have smooth rotation) hoses, watch for any leaks, clean air filters, don't idle too long, until oil is up to temp be easy on the throttle, and avoid starting the engine unnecessarily. We are far more likely to have something external break that does damage than anything internal. Last but not least drive them at least once a month for 20 miles or so if you are not traveling. Just my 2 cents....

Later Ed

One important thing I forgot to mention is that the CAT representative did say that the use of synthetic oil does not increase the reccomended oil change frequency requirement for warranty purposes.