TLTrance

My first two oil changes (around 5.2k and 10.7k) used Dino oil... My third oil change at 16.3k, I used Mobil 1 synthetic...

My question is: Is it okay to switch back to Dino for my 20k (actually its closer to 21.8K) oil change?

I'll still be using my own filter, but the reasons I'm asking this is:

1. Sometimes I just won't have time to get the synthetic..
2. I plan on following the MID anyways, hence dino should just do fine (I don't plan on doing extended drains, contrary to what I thought before)
3. Mobil 1 syn is hard to get around here (I tried in 4 separate places, three times, and no go except for the last time around)

Boulder GT3

Mobil 1 is hard to find in SJC?

It's fine to switch although the precision and tolerences of the TL motor are best served by M1. Oil reports are tedious beyond belief but the net is that syns really do have much better sheer levels especially at high temps.

Some people say that old engines will develop leaks in the seals and gaskets if you switch back and forth between dino and syn. I've never seen it and tend to not believe that but it's a legend.

KJSmitty

Switching will not hurt a bit TLFrance. Not sure what you plan on using but many mechanics have suggested sticking with one brand once you start is better than not.. Once again though, your one oil change with M-1 will not make a difference
Overall, all oils/brands are mandated by law to be compatible with each other etc..

In older engines and initial blends of synthetic oils, going from Dino to synthetic actually would cause leaks.. Not the case now. In the past it had to do with an incompatibility between seals and synthetic.. I can't remember but the seals either got really soft or really hard... Either way they leaked afterwords.. Don't remotely think you will have this issue though..

I myself tend to switch between Castrol full synthetic and their "Syntec blend".. Like you, it all depends on what they have in the 5 quart jug that day on the shelf at Walmart... I too however stick with one filter,, the M110.