The Stovebolt Site Forums The Shop Area Engine Shop Chevy 235. Is Synthetic oil damaging or safe?

not sure if this has been asked but whats the deal with synthetic? a old friend of mine says it will damage the main bearings. i have a newly rebuilt 235 from 1954. solid lifters, upgraded main bearings, brand new seals etc. it only has 5,000 miles.
i dont have an issue with rotella or the high ZDDP valvoline but im just wondering what makes these older engines "incompatible" so to speak. obviously if you ran synthetic in a old engine not rebuilt it would leak more, but other than that i dont see an issue. the technology has evolved an extreme amount since the 70s, which alot of these old timers are still in education wise. there was a gentleman i met who ran royal purple in his (original) 57 chevy with no issues. is it all a bunch of outdated and conflicting knowledge or is synthetic genuinely harmful to older (but rebuilt) engines? please let me know. i dont know all that much about oil, and if they phase out non synthetic, i want to have knowledge for the future.

Most synthetic oils are extremely thin in consistency, even if they have a high "hot" viscosity rating. They're still water-thin, no matter what the operating temperature of the oil happens to be. Stovebolt engines have minimum oil clearance specifications when freshly rebuilt that are beyond "worn out" numbers on modern engines. Most synthetics simply don't provide enough cushioning effect between parts to prevent noisy operation and possibly low oil pressure and damage from parts hammering each other due to the extreme thinness of the oil.

For instance, 5W-30 or similar viscosity synthetics simply don't have the physical thickness of the 15W-40 oil I use in every engine on my place, from Diesel farm tractors to cars, trucks, lawn mowers, welders, pressure washers, and a few other pieces of equipment with 4-stroke engines, even a Harley soft tail with an EVO engine. No oil-related problems in over 30 years, and it's a lot less expensive in 5-gallon pails from the local farm store!
Jerry

If your engine is otherwise in good shape, clearance wise, the only thing synthetic will damage is your pocketbook. It's too darn expensive to consider even in modern engines. There's really no benefit, but also no real potential for damage.

Another oil debate. I'm no expert but I'd side with Jerry about the viscosity unless you can find a synthetic with a higher cold viscosity. I'll have to respectfully disagree with Kevin about there being no benefit. Everything I've read indicates far superior wear protection with full synthetic. I use 15W40 Delvac oil in my 38 and 53 for the higher cold viscosity but full synthetic in my 18 year old pickup (since my first oil change). I'm still using dino oil in my Charger since that's what's called out in the service contract. When the service contract is up I'll be switching to synthetic in it as well. I use Walmart brand synthetic. It's MUCH cheaper than the name brands and meets the same spec. The Walmart brand full synthetic is also cheaper than dino oil in 5 qt. cans.

If you don't drive a lot of miles every year, the synthetic might be a good a choice. I run Mobil 1 in everything I have including the 250 in my '37, have been for many years. I don't drive a lot miles, but I do a lot of short trips. Can't say if it helps or not, but my newest vehicle is 18 years old and still running strong. If you watch for sales, synthetic is not that much more money. Valvoline makes NAPA oil, so its always a little cheaper then the rest.

Yes, 15 is greater than 5

Here is my personal experience with synthetic oil. In October 2001 I became the Police Chief of a small town about 30 miles south of my home. As is with most small towns we drove old worn out castoffs from out of state hiway patrol departments. High mileage crown vics. We were changing oil every 3000 miles and adding 2-3 quarts between changes. I convinced the town council to try synthetic oil on my unit since it was being driven the most. Oil consumption went to zero in the 3000 between changes and the rest of the fleet was changed to synthetic at their regular change. Each unit saw the same results. This is just my observation and not meant to be an endorsement of any synthetic oil.

My opinion. I drive a 2000 silverado with the 5.3. Have used synthetic since the first oil change in 2000. Have 235000 miles now and still runs like a champ. Never any internal engine work done up to this day. Costly yes. But so are engine repairs

I found in using synthetic for the life of one of my vehicles that it kept the internals very clean .l had a valve cover leak and the cover was one with a built in gasket so I got a older valve cover that used a gasket from the junk yard and I could not clean the inside of that cover to get it clean compared to the one that was on my vehicle .the car lasted 25 yrs and went to the scrap yard with a rusty body and a perfect running engine .I would be careful if you put synthetic in a engine that had regular oil used for many miles maybe use a synthetic blend for a few oil changes then go to synthetic.

after a good amount of research, the type of oil really doesn't matter in a old flat tappet engine, as long as 2 things are kept in check: proper viscosity for the driving conditions, and a proper amount of ZDDP, which provides the cushioning effect for the cam and any other loose clearance parts in the engine. its also important that your seals are good if its a particularly old engine with a lot of miles or age, as synthetic can cause more consumption of oil or leaks.
after knowing all of this i will be making the switch to valvolines racing high ZDDP oil. diesel oil is perfectly fine but it seems to hold more of the deposits created by the engine, despite having a good filter. its not too much more and for someone who wants a lot of life out of my 235, that's what i will go with.
i change my oil every 2000 miles anyway, which is every couple months, as my truck is a daily driver, and i dont feel like adding ZDDP to my oil every time i do a change.
i also use a quart of lucas oil stabilizer, which would add the necessary viscosity to any synthetic i might ever add to it. it also helps my oil pressure and overall cling of the oil.

The synthetics are fine for a modern motor, they were designed to use them. But our older motors were designed for Dino oil, at a certain thickness, a certain viscosity, certain flow characteristics, with certain additives. As pointed out by hotrod Lincoln, the thinner full synthetics find the path of least resistance and have a higher tendency to leak, think that pesky rope seal, don’t provide the appropriate amount of cushioning, and thus may not be the very best choice.

There is one alternative, brad Penn, now called penn grade 1, is a Dino based oil, with the zinc for the cam, and a synthetic additive package. Termed a semi synthetic. I run that stuff in my 235 and 261 motors and have done so for quite a few years, and I am not easy on my motors. Not a single hiccup on any motor I have used it in. They also make what I think is a terrific break in oil.

Just an alternative.