Changing her engine oil to synthetic

[71CHEVYSHORTBED402]

Just some history. She blew a cork the day I was fired because the boss was a Dk. Abusive guy, they didn't need a reason and didn't, short I saw him in his office getting a lap dance. Geez, lost my Sheba two days later. On the bright side, it allowed time to tend her, and the place hired me back a month later for more $.

I was fairly green mechanically, but my buddy helped me R&R at his place and equipment, all while I sprayed parts, and an engine bay without taping stuff off 0F-30F for days☺....Actually held-up, and what a poor job That was 1993, I believe 99K on the 402, daily driver following a rough winter.

The engine rebuilder was real good, I caught him before meth took his skills away, and life literally. 40,900 on that engine today, in short I had no reason to replace it for a restoration. I used Durablend 10-40 and 20-50 with great results. Short too many leaks Come to think of it, our R&R couldn't have been that great, standard gaskets perhaps, even old Durablend will find leaks. Today's best gaskets>>>standard, and on that note, the pans take longer bolts, so ARP>>>factory bolts for the job too.

She purred with 20-50, but they changed the formula, so I found information on this website pushing Mobil-1 Full S 5-30. At your own risk, miles may vary. But here's the thing, my experience. I didn't like the way my engine felt and thought bummer. But is what it is, once full synthetic engine oil, I've heard you can never go back.

So happened this was the last oil change before the engine was put to sleep 6-7 years, for a restore, seems perhaps another for a very short duration.

With the maiden start, the engine felt better than I remembered, and really, it's been changed another three times over 900 miles Today its never ran better. No leaks with the good gaskets, so far

It's just that in my experience, IMO, when you switch oils, especially to full S, run it a short while, and then change it again.

[Willshook]

Just remember that if you have a flat-tappet cam, you need 1000 - 1300 PPM ZDDP - which that oil does not have.

https://www.mobil.com/lubricants/-/m...5A6CCC91BE38D9

Synthetic oils tend to have a higher solvency - it's one of the reasons that when you tear down an engine that's had a steady diet of synthetic it's incredibly clean.

When you swap on an older engine, two things tend to happen. 1) the higher solvency tends to clean out quite a bit of gunk and a change after a few thousand miles is a good idea. 2) it sometimes cleans gunk away from marginal seals - so you hear sometimes that an engine only started to leak after synthetics; this is often the cause.

[un4gvn!]

I have a ZZ454 in my 69CST. The booklet that came with the engine said to run full synthetic oil, so I did. Ran it for years with that type of oil. Last summer I changed the oil to convential. Seemed to run the same up until Labor Day weekend. I checked the oil and it looked super thick on the dip stick. I was done for the summer and fall. I pulled the engine figuring on putting in a ZZ502 cam swap , timing chain, roller rockers and complete tear down just to check every thing out. It started leaking oil, so all new gaskets from GM Performance also. I used their gaskets because of the aluminum Heads. What I'm getting to because I change oil types is when I pulled the oil pan, the oil looked like real thick pudding. It was a pia to clean up. It was all through the engine. I had to take the whole engine apart to clean it out. So my suggestion is don't mix the oils. I'm not sure if thats what happen, but I never saw this happen in all my years of working on engines. I didn't have any engine damage. Maybe I got to it before it would happen. I installed the engine right before Christmas and it seems to run good so far. I won't really know how it runs til the weather gets warmer. Just my 2 cents.

[70STOVEBOLT]

Why would you not be able to switch back to dino oil from synthetic?

[un4gvn!]

I changed to convential from synthetic. There's always left over oil in the engine from the last oil change. My guess is when the left over synthetic mixed with the new oil something happened. I also use top name brands of oils. I'm not saying that's what happened to my oil, but it was the only thing I changed.