Safe to use synthetic oil on my Ebay truck?

[Randee of the Redwoods]

Mileage now stands at 183,000. Wow. The only downer is the service history. You've all heard the stories of the "whacka-whacka-whacka" I have to listen to in the morning. It goes away by the time I get to work about 10 milutes and 4 miles later.
Well, seems the local Advance doesn't stock normal Rotella all the time, but the have a buttload of synthetic. The syn oil is 5-40, much thinner at startup. Would it be safe to switch over assuming normal Rotella has been run in the oil in the past? Oil change is due now so oil testing will probably have to wait for the next 2000 miles. I THINK normal Rotella has been used in this truck in the past because the oil change minder sticker on the windshield, which is current, has the Shell Rotella T logo on it.

[moedog]

IF YOU KNOW WHAT THE PREVIOUS OWNER USED I WOULD CONTINUE WITH THAT KIND OF MILEAGE. IF YOU DO USE THE SYNTHETIC I RECOMMEND THE DELVAC MOBIL FOR DIESELS. ITS ALL I USE. IF YOU SWITCH AND THE NOISE GOES AWAY OR GETS WORSE, LET US KNOW!!!

[richard7]

You can use either no problem.

Whatever diesel oil you chose, if you permit, I suggest you do an engine flush to clean carbon and varnish deposits that have accumulated over the years. You can even do 2 treatments in a row if the inside of the engine is bad. This will usually reduce engine noise (because the lifters will work more freely) and can decrease oil consumption and add compression if the rings were stuck in the carbon. This has worked multiple times on older engines I did.

After the flush, this is a good time to introduce synthetic oil as it is keeping the engine cleaner than mineral oil. But using a recognized mineral oil is adequate too.