I might have killed my 65 Chevy, synthetic v/s conventional oil

I thought to myself what a great idea, let’s change from conventional oil to synthetic nothing but the best for my old 65, c-10, 6 cylinder. Now she smokes all the time. Tell me it is not too late to switch her back to conventional oil. I have been told yes I can and no I cannot. Can someone give me the skinny on what I may have done that can or cannot be undone?

Yes you can switch back. But closely monitor the amount of smoke. If it continues to be the same, then I would try a heavier weight oil to see if it helps.

The synthetic oil shouldn’t matter one bit…But if you think it does…just switch back…it won’t matter at all.

Assuming you use the correct viscosity, you can switch from conventional to synthetic, and back again, at will. You can even mix them if you choose. The engine doesn’t care.

Personally, I don’t see any benefit in using synthetic unless the owner’s manual specifies it, and I continue to use conventional oil in my vehicles. What made you want to switch?

I can’t explain the smoke.

What color is the smoke?

My guess would be valve seals, because I can’t think of a reason that synthetic oil would affect oil scraper rings. They may get a little better after you switch back, but don’t count on it. If they don’t improve, replacing the valve seals on that engine won’t be a big deal.

I know that the synthetic oil enthusiasts are certain that switching to synthetic oil in an older car does not cause oil leaks, but my personal experience indicates otherwise.

Those who say you can’t switch between synthetic oil and conventional oil are perpetuating a myth. You can switch as often as you like, and it won’t make a difference.

There is a strong chance this was coincidence, and it wasn’t caused by the oil, but you should switch back to rule it out as the cause.

The folks who believe that you can’t switch from synthetic to conventional motor oil are probably the same folks who think that placing a knife underneath your bed will cut your pain in half. Old wives’ tales are best left to history, rather than believing them.

Dino oil and synthetic oil are chemicaly exactly the same. the only differences are that synthetic has fewer impuities and its molecular size is allegedly more consistant. They can be switched back and forth and even blended. You can even buy them already blended.

As to your oil burning issue, the synthetic had nothing to do with that. On an old engine without a turbocharger there are two common passages for oil to get into the combustion chambers and burn.

One is past the piston rings. Typically a piston has two compression rings and one oil wiper ring (actually an assembly with two wipers and a spacer). The wiper rings are designed to press out against the cylinder walls with spring tension and wipe excess oil from the walls as the piston comes down. They can, due to wear of the cylinder walls and the rings as well as loss of spring tension, begin to perform their function less than efficiently. That, combined with wear and loss of spring tension of the compression rings, can leave too much oil on the cylinder walls that can be allowed to remain on the walls as the piston recedes and pushed back up into the cylinder and burned with the fuel. Typically this will show up as grey smoke upon acceleration.

The second is valve stem seals. Oil that lubricates the valvetrain flows back down to the oil pan through “returns”, which are simply drain channels. It’s kept out of the cylinders by seals arouond the valve stems. If these seals wear, they can allow oil to be drawn past the valves and into the cylinders during the intake strokes. Typically this will show up as smoke on start up, because overnight the oil runs onto the back of the closed valves and into the open chanbers and burns upon startup, and/or as smoke on deceleration, because during deceleration vacuum spikes and pulls the oil past the worn valve stem seals at every intake stroke.

I suppose it is possible that you “washed” gummed up oil rings with the synthetic and exascerbated an existing problem, but the real cause is wear. I’d suggest a compression test of the engine as well as a vacuum test. Together they should give you an idea of the general condition of the insides of the engine.

I think some of the myths about synthetic oil may have started back in the 1950s when detergent oil became popular. My dad switched to detergent oil in his 1949 Dodge and the oil consumption shot up drastically. The detergent did have a tendency to remove carbon from the oil rings in engines that had been using non-detergent oil. However, unless you were using non-detergent in your Chevrolet, I doubt that the switch to synthetic caused your engine to smoke. It would be interesting to know what viscosity oil you had been using and the viscosity of the synthetic oil you put in the crankcase.

Thanks for all the input. Looks like we going to replace the valve stem seals. A freind came by last night and put me at ease. He as Waterboy strated with the what color smoke and explained going digging backwards what dould be the issue.
Thanks to everyone who placed a comment for me.