i have an 84 el camino that has 10w-30 oil can i switch to mobil 1 synthetic without any harmful side effects?

Yes you can switch. I ran the LT1 in my El Camino with dino oil for the first 3000 miles. Now it's running Mobile 1. That's all I've used in my Camaro and with about 49k miles it's still running great.

Sexy84;

Question: How many miles on the engine? Has it been rebuilt?

The Synthetics are good oils and hold up well under heat. They are also a more consistent sized molecules. They do not stop leaks or repair worn out parts.

Because the Molecules are more uniform they can show a leak or make a small leak look worse than it did with Dino oil. Dino oil is fine too if you keep a regular change 3000 to 4000 miles and clean filters.

Mobile 1 impressed me a long time ago. I wouldn't bother with it in a old used engine that already had a lot of miles. It is more expensive and if your engine burns oil or leaks then you'll pay a lot more to keep oil in it with the Synth oils.

Just my input

my engine has 76,000 miles and the engine runs fine so far and never has been rebuilt