I've been using Mobil 1 in my '63 super 88 w/394 cu in engine.
I recently saw an article that said that synthetic oil may not be good for engines with "flat tappets". I'm not technically astute. But, does the 394 engine contain flat tappets?

 

Never heard that one and yes your olds 394 does fit the discription. Where is the article. I would like to read it.

 

Was your 394 rebuilt anytime within the past few years.

Syn oil is much thinner than conventional of the same weight, it can find holes in gaskets and leak out pretty quick

 

I have the 63 super 88 for 5 years. It was a frame off restoration about 15 years ago. I have pictures with the engine and transmission out of the car, but don't know if the engine was rebuilt. When I got the car, there was an occasional tapping at highway speeds. A mechanic who worked on the car took off the valve covers and said that everything was perfectly clean. He advised me to use Mobil 1 (10-30). Since then, I haven't heard a noise and haven't had any leaks. But, on 1/2/09 in New York's Newsday newspaper, in the car question section, an ASE certified Master Tech stated that synthetic oil is great for late model engines with roller camshafts and lifters. But recommended that special additives be added to engine oil of older cars. I read another article, which I don't recall the source, that stated that synthetic oil should not be used in engines with flat tappets. I haven't had any problems. Does anyone have any info pro or con? Thanks.

 

ALL current fossil oils need additives for safe use in older engines. Anything past API SJ rating needs them. SL/SM are fine for roller cam engines. I'm even leery of newer "clean" diesel-rated oils, though they still have more anti-scuff additive than any modern spark rated oil.

That was always one of the big selling points on synthetics, that they had better lubricity and would not drain off engine components like dino oils. Except for the aforementioned leak-finding propensity, a synthetic should run fine in a flat tappet engine. That's all that were available when synthetic oil formulations first came out and those engines did fine on synthetics.

If the engine runs quiet and uses no appreciable oil, I think you'll be OK to continue using synthetic in it. If you go back to dino oil you may create a whole new set of problems.

Upper valvetrain noise is common on 394, as is heavy blowby after they get some miles on them. The synthetic may actually help those conditions.

 

The engine starts right up, runs quietly, doesn't smoke, and doesn't burn oil. I've been using Mobil 1 (10-30) for five years.
Thanks for the replies