I was a quart low in oil and found some unused Castrol Syntec in my garage and I used it to top off the Mobil 1 Sythetic currently in my car. Should I be ok. Both were 5w-50. Just wanted to get folks opinion on this.

 

Bump.

Hmm. Setting the stage for fighting oil additives perhaps?

Seriously, I'd like to know about this question as well.

 

When I did my European delivery of our Boxster S we spent 2 weeks travelling around the Alps. After about 2000 miles I suddenly noticed that I was a quart low and desperately tried to find the factory fill Mobil 1 0W-40 to no avail. Eventually I found a synthetic Shell oil in the correct weight and finished the trip without incident.
When I got home I was going to do an oil change anyway and decided to ask the head of Ethyl Oil Co R&D department (who was a client and good friend) if I did anything wrong.
The short answer was that it was probably OK and certainly better than not putting anything in the car but it would be a good idea to change it out which I did.
Hope this helps.

 

To meet spec they have to be fully compatible. For my daily driver/beater oil changes I have often made a 'Wapatui' of whatever lefotver oils I had laying around and never had any sort of oil-related problems with them. The shopping cart related problems I had, were probably not a result of the oil mixture.

I frequently mix synthetic and dino oil, but I try to stay with the same company. I might fill with Rotella T synthetic and top off with Rotella, for example. But I have topped off many cars with any good oil. No problems. Remember there is a ton of oil left in the car after you drain so oils have to get along.

Again to meet the spec they have to be fully compatible.
-Joel.

 

Seems kinda late to be asking after the fact!!