Originally Posted by zztopgun
Got my 05 GC 5.7 with 90k on it and I have no idea if the previous owner used synthetic or not. I heard it can be bad to use full synthetic if it wasn't previously used. I'm just looking to get optimum engine performance and protection. I currently have a blend in it but most places don't offer blends for oil changes and I don't trust the jeep dealers. My local lube shop only offers regular or full synthetic. Any opinions and advice are greatly appreciated!
I would suggest using Seafoam or some other oil treatment before you cut over from synth blend to full synth. However, you could just use ordinary oil for changes and keep a bottle of good synth for topups, particularly if your dealer leaves it a bit low.
If you've been running oil good enough for the MDS, your engine should be pretty clean internally, enough you could cut over, and if you've been using a good synth blend, that would also do a good job of cleaning it out.
Still if it were my hemi, I'd Seafoam the oil soon after a change, run it a few hundred or less, then change again. If you are ultracareful, use your blend and keep an eye on it for contamination, then just cut over to full synth.
A good independent mechanic that knows the hemi's with mds should be able to tell you if you need to worry about cutting over.