Is it unnecessary to use both Sea Foam and sta-bil at the same time in two stroke and four stroke engines, or is it advantageous to take advantage of the properties of both? Both products claim to clean internal engine parts.
Sta-Bil and Seafoam are made to do do two different things, but there is some overlap. If you are regularly driving or using a vehicle, there is no real need to utilize Sta-Bil. Its purpose is to keep moisture from contaminating the fuel. Moisture is the main enemy of fuel. When you are burning through your fuel on a regular basis, it won't have time to absorb much moisture so it won't contaminate your fuel. I have never heard of Sta-Bil causing engines any issues.
The purpose of Seafoam is to clean the intake tract (to include injectors) of the engine. It does a little bit of fuel stabilization, just like Sta-Bil does a bit of engine cleaning. There is no need to use both at the same time, though it wouldn't hurt anything if you did. I routinely use Sta-Bil in the gas for my generator and other small power equipment. It keeps fuel good for at least two years. I use Seafoam only when I need to clean the engine.