The Stovebolt Site Forums The Shop Area Engine Shop If I change from reg. oil to synthetic do I have do

anything special, like a special flush?? 235 chevy engine restored.

Done this many times. If the engine has been "run in" on break in oil and changed a couple of times. PIck your synthetic with adequate levels of Zink and phosphorus. I use Amsoil 10w40 which has plenty of both, there are others.

I thought switching back to Dino oil improved your leaks? Why would you go back to synthetic?

JW. it is in furtherance of my effort to determine why my MPG has dropped. I plan to drive to Dayton Ohio next Saturday for the Vintage Truck Show before I make further changes. I replaced the PCV the other day. I am thinking of replacing the HEI but for the $200.00 it cost I can buy a lot of fuel. New shocks are being installed Monday and I am reasonably sure that is not the cause of the MPG drop. .

Going from memory of the other thread.....this is the first major highway trip since your mechanic found and (hopefully) fixed a carburetor issue.

My 2 cents:
* Change one thing at a time so you know what's what. Let this be the trip to evaluate the carb thing.
* Oil isn't going to change MPG by a measurable amount. If it needs changed, change it with whatever you're running now....just to keep it a constant.
* Unless there's solid evidence to suggest at HEI problem, leave that alone for this trip.

When it comes to mechanical things....I am very prone to throwing "stuff" at the wall just to see what sticks. It's an urge I am slowly learning to resist. Most recent example for me is my backup chainsaw that suddenly stopped running. Trying to methodically test and eliminate theories about compression, spark, and fuel.

I believe there are a lot more downsides to synthetic oil in a stovebolt than the alleged advantages. Just go flush a few bucks down the toilet- - - -it's easier and quicker than wasting the same amount of money changing oil.
Jerry

Synthetic vs. Dino oil has been debated since synthetic existed. Lots of guys on the Diesel forums swear by synthetic and do extended oil changes.
The main advantage is it has a wider viscosity range (called viscosity index in the trade) than Dino oil. Where you can get say 5W-30 or 15W-40 in Dino, you can get 0W30 or 5W-40 in Syn

The myth about synthetic leaking more than Dino oil is just that -- a myth.

Like Jerry said, you might as well flush the money you'd spend on Syn oil.

It's normal for the old engines to burn about a quart per 1000 miles. Why burn the expensive stuff? Use the Dino oil.

Back in the 50's Prestone came out with a manufactured oil. The American way "if it cost more it must be better." Cadilac dealers started using it in all their cars. They soon found out the upper piston rings started wearing out. They had to do a bunch of o-hauls under warranty. It was soon discontinued. That has always left a bad taste in my mouth about synthetic oil.
Some things are just better naturally. Wood is still one of the best building materials. Cotton & wool are still the best fabrics. Remember the Dacron suits from the disco days. I stick with Petroleum motor oil except my late model car that specifies Synthetic. The only real advantage to syn. is it doesn't leave carbon deposits from high temperatures.

George

There is nothing special that needs to done to start using synthetic oil. I think its more important to pick an oil with a good additive package and Heavy Duty Engine Oils are recommended for flat tappet valve trains by the Corvair Oil Guide. See Engine Wear. An excellent synthetic HDEO is Rotella T6 5W-30 and I like semi-synthetic Petro-Canada DURON SHP 10W-30.

Nondetergent oils were used when Stovebolts were new so any modern multigrade oil would be vastly better. ZDDP is the antiwear wear additive in engine oil and its actually the phosphorus that provides the antiwear function. OEM-style valve trains don't need much more than 800 ppm of phosphorus and amounts over 1400 ppm are not beneficial. See Engine Oil Myths - GM TechLink.

If your engine uses much more than 1 quart between oil changes, I would be more inclined to stick with a lower cost conventional HDEO.

See YouTube: Is Synthetic Motor Oil Good for Everyday Cars?

If your fuel economy suddenly dropped, the cause should be reasonably easy to determine. It's not clear whether you already have an HEI ignition system or are thinking about upgrading. HEI is an excellent ignition system and is very reliable, especially if the ignition module is kept cool.