Fuel system cleaner yay or nay?

Will a fuel system cleaner added to the gas tank cause any negative effects? Other than maybe a dirty fuel filter. Is it even necessary?

Will a fuel system cleaner added to the gas tank cause any negative effects?

If used as directed - NO.

Is it even necessary?

Every once in a while it might be a good idea. Especially if you have a newer back-flow filter system. The filter is in the tank and you don’t want that failing - because you have to pull the tank to replace it.

On a fuel injected engine it might be worthwhile to add a good fuel system cleaner occasionally as preventive maintenance. A bottle of Techron or Sea Foam might prevent varnish from accumulating on check valves and injectors and it won’t harm anything. For the meticulous add a bottle at oil change time. For the “if it ain’t broke don’t fix it” crowd odds are you won’t benefit from the cost.

I’ve never seen any evidence that it provides any benefit on a properly maintained vehicle driven often enough to keep the gas fairly fresh, but I’ve also never seen it do any harm as long as it’s properly used.

Maybe I am superstitious, but I believe in a you treat them well and they will treat you well. I do an occasional dose of seafome and use mid grade, sure it is a waste of money, kind of like flowers that will die for the wife, hoping there is a payoff in the end but there are no guarantees.

I’d only use it if there is a reason to do so. Not as routine maintenance.

I'd only use it if there is a reason to do so.

By then it’s too late.

I think additives have their place. They can be invaluable for squeezing an extra six months or more out of a worn out old beater. But I don’t think they have any place or serve any purpose in a well maintained decent vehicle. Cars today are well designed to operate on the fluids provided by the manufacturers and on pump gas, and gasolines are blended with sufficient detergents to keep a car running well.

I’ve experienced Techron smoothing out a rough idle. It also restored power in my chainsaw.
I put a bottle in my car’s gas tank once a year.