Synthetic oil is meant for extended drain intervals. If your gonna change it at 5000k don't bother with the added cost and go with conventional. And there is no harm in going back and forth from syth to Dino oil. That is nothing but a fairy tale. Red line is good AMSOIL and royal purple. Mobil 1 is not a real synthetic as it uses hydrocracked Dino oil as base stock. Join the bob is the oil guy forum. There is some enlightening info there.

My preference goes like this
Amsoil
RP
Mobil 1

Of coarse each to their own

I use Mobil 1. As long as you buy brand name oil and change it when needed you will be fine. Synthetic doesn't hurt but I don't believe in using it to extend the distance between oil changes. It still gets dirty no matter what it is.

I used Castrol Synthetic Blend 5w-30w, mind you I don't have a Gt.

yea but i bet that 4.0 is in better shape than most GTs :tup

I totally disagree with there being no harm in going back and forth from Synthetic to regualr engine oil, and actually to take that it a step further, I would not even switch brands of oils. You need to understand that every oil company uses different chemicals, and different processes, to refine their oil, and in some specific cases, these chemicals cannot be mixed, and if they are mixed, even in the slightest, it can cause a major reaction in the viscosity of the oil, and possibly result in damage to your engine! Also, do not, I repeat, DO NOT use additives. Here is a link I posted a couple years ago on this forum, and it talks about engine oils, and aditives.

http://www.carbibles.com/additives.html

Oh yeah, I forgot, I use Mobil 1 synthetic, and would suggest either that, or Amsoil. Both very good engine oils.

Essentially it is just like it came off the show room floor, with about $10,000.00 other goodies on it. For a sleeper she purrs along pretty good.

I tend to agree with you regarding not switching brands. But sometimes you are let with no choice. For example from the time I got the 05 until early last year I was using Quaker State 5w-30w High RPM Oil as this was the oil that was recommended in Mustangs and Fast Fords. In the fall of 2009 Quaker State for whatever reason discontinued the High RPM Oil so I had no choice but to switch to a similar product by Castrol. I have used castrol before in my other mustangs and have no problem with the Castrol product. I would rather have had the Quaker State High RPM Oil because I am not a fan of switching oils, unfortuanately, I along with probably several thousand others was left with no choice.:?

I have the oil changed at the dealership (I know lol ) and they use 5W50 Mobil 1 Synthetic and I have no problems with their selection. I generally put no more than 500-800 miles on per year so the oil is in good/great shape when dumped. With fuel/oil prices going up I wonder what the oil change will cost me this year. Last year for 7 liters and a filter the bill came to 112.00. I will let you know in 2 months.