My car (a 2008 Scion tC) says to have its oil changed every 5K miles or 5 months. I just took a new job and commute into the city by bus so I'm driving a whole lot less. I was told that if I got full synthetic oil on my next oil change, I could simply wait for 5K miles before my next change and forget about the whole 5 months. Is this true?
The synthetic oil should last longer without degrading, so if you are doing less miles this should safely extend the oil change period.
Check with your garage that you get the correct synthetic oil.
I think it really depends. If you live in an area that can get into lower temperatures (way below freezing) it'd be wise to get lighter oil put in by winter time, and thicker oil by summer time. If the climate is relatively stable this isn't as much of a concern. This is a case where, not necessarily 5 months, but bi-yearly would be a good idea.
When you do end up driving your car be sure it can get up to normal operating temperatures. Otherwise the water (and whatever else) that has collected with the oil in't removed and can lead to oil sludge.