Synthetic oil is definitely the way to go in my opinion. However be aware
that the claims of longer life are both true and false. It is true that
the oil itself lasts longer before breaking down but... It still gets
dirty at the same rate based on usage, so don't go thinking you can run it
for 20k miles before changing.
My wifes newest Jetta is a Syntec user. Honestly though the car sits most of the time (less than 3k per year). Her work Jetta is an '85 that I got from the original owner with only 96k miles in '99, he ran only Mobil 1 since new. Since then she has put another 150k on it and it gets Syntec every 5k. Other than normal (anal) maintainence on my part it just keeps going. The head has never been off and it still has 140-145 psi compression in all cylinders.
There is a downside to switching over on an older car. You can expect to see increased oil leakage. If there's a hole it'll find it. Any quality brand should do the job just fine. Just don't try "Billy Bob's Super Duper motor oil". ;)
As for the "high mileage" oils, with all the cars I see going through my shops I can't see any benefit in them. The only difference I'm aware of is chemicals to soften your seals to decrease leaks. You can do the same with oil additives for less money. Hope this helps, good luck.
I'm trying to decide whether or not to switch to synthetic motor oil.
I know there are lots of opinions out there but it looks like the majority points to using the more expensive stuff. I have an older car (1991 Jetta with 125K) and a newer car (2002 VW Eurovan with 10K) so I'm wondering if I should use synthetic in the new car and keep using regular in the older? There are now "high mileage" motor oils available too. It's very difficult to decide with all the info out there.
Assuming that synthetic is the way to go, does brand matter? Costco sells Mobil 1 and the price is extremely competitive. I've always used Castrol in my older car so should I stick with Castrol and go to the Syntec?
I would really appreciate your advice.