I have an old toilet that has a tank that hold approx 3.8 gallons of water. When I flush the toilet an enormous bubble comes up before it flushes.

A handyman checked the roof exhaust pipe as well as the one in the ground and said there did not appear to be an blockages. He recommended getting a new toilet.

I had a plumber look at it and he said the same thing, new toilet.

Does this seem logical. Friends have said that seem ridiculous and unlikely to be the cause of a gigantic bubble.

Thank you!

Actually, I had a toilet that did the same thing. It was a cheap entry level toilet. I replaced it with a American Standard Cadet and the "bubble" disappeared.

Welcome to The Plumbing Page at AMHD.com.This was a working toilet, correct? I don't think that replacing the toilet with a new one will solve your problem.
You have a partial clog in the drainage line. Let me explain what's happening. You flush the upstairs john, The discharge picks up speed and bangs into the partial clog in the line and starts to rebound back pushing a bubble of air ahead of it. This is what you see in the f toilet. Then, because it's not completely blocked the discharge drains away before anything overflows. This can only get worse. The drainage line that services the toilet needs to be snaked out or if you're on a septic tank it should be checked to see if it needs to be pumped. Hope this helps and thank you for rating my reply. Tom