Synthetic oil..

[mora]

Yep, good synthetics will last 10,000 miles/1 year in almost any engine and sometimes much longer. In the US the service intervals are shorter because of lower quality oil. Infact it's a good way for manufacturers to milk the customers by not demanding the use of synthetics, as they can require shorter service intervals. All the new gasoline powered cars sold here have 12,500 ml or 18,500 ml service intervals.

[storch]

The function of oil, besides the obvious lubricating properties is also to suspend and neutralize the by-products of combustion and other contaminants that make their way into the engine.  

The oil filter strains out a portion of these but in time it (the filter) becomes clogged from these harmful deposits.  Once the filter cloggs up then the oil in the engine will continue to flow but it will no longer be filtered.  Guess where these harmful deposits end up.  

The maximum I would go with an oil change interval would be 3 months irrespective of miles/hours driven.  This is because as your engine cools water condenses within it.  This water when combined with the combustion by-products becomes an acid.  This acid wreaks havoc with your crankshaft bearings and other moving parts.  The water also causes electrolisys between dissimilar metals. Frequent use at operating temperatures evaporates the moisture therefore in that sense frequent use is beneficial to the overall life of an engine.

The less you drive a vehicle the more important it becomes to change your oil frequently.  

I sometimes drive up to 200 miles in a day and seldom less than 100 miles every day, 6 days a week.  I drive fairly fast (70-80 mph/ 120-140 kph on the interstates slightly slower on county roads and a little slower still on streets and parking lots) given the conditions and if they permit as I live in a high poplulation density area.  many of the my fellow motorists are from the third world and are known to de driving at under 40 mph/75 kph on the interstates and even slower on the county roads.  I try to sprint past these types of drivers to obtain a better position at the next light.  I can usually cross town in a fraction of the time it takes other drivers to cover the same distances.  I do quite a bit of up and down shifting consequently.  

My engines get a great workout every week.  As I've stated before I manage to have structural failure on my vehicles due to oxydization but never engine failures.  Current vehicle is a 1999 Toyota Tacoma current mileage is 240,000 +  Never fails.  And yes I'm sure this exceeds the Mfg's. MTBF expectataions.  Do you think I'll get as many miles from the Toyota as I did from the Ford?  The Toyota is already showing some rust.

[mora]

"The function of oil, besides the obvious lubricating properties is also to suspend and neutralize the by-products of combustion and other contaminants that make their way into the engine.  

The oil filter strains out a portion of these but in time it (the filter) becomes clogged from these harmful deposits.  Once the filter cloggs up then the oil in the engine will continue to flow but it will no longer be filtered.  Guess where these harmful deposits end up. "

Correct. If you use the same filter long enough that's what happens, that will take 20,000 miles though. That is why engines with longer oil change intervals are fitted with bigger filters.

"The maximum I would go with an oil change interval would be 3 months irrespective of miles/hours driven.  This is because as your engine cools water condenses within it.  This water when combined with the combustion by-products becomes an acid.  This acid wreaks havoc with your crankshaft bearings and other moving parts.  The water also causes electrolisys between dissimilar metals. Frequent use at operating temperatures evaporates the moisture therefore in that sense frequent use is beneficial to the overall life of an engine. "

That is an issue...but 3 moths is overkill. If you wan't to be on the safe side then you might want to change it every 6 months.

[lazs2]

I use mobil one and redline.

I change oil every 4 months or so regardless..  the reason that you can't use synthetic in a new engine is because it prevents heat and wear so well that nothing will seat.

lazs

[Wanker]

I use Mobil One 5w30 in the winter, and 15w50 in the summer. I seem to get better mileage using the synthetic, and for cold weather starting, nothing is better.

[rpm]

I use Valvolene 15W40, but I also add Prolong. That stuff is GREAT!