Extreme STIHL String Trimmer Durability Test: Can the FS 91 Survive It All?
When it comes to string trimmers, the STIHL FS 91 has built a reputation for being a rugged and dependable tool. But how tough is it really? To answer this question, we took the FS 91 through a series of intense durability tests designed to push this professional-grade string trimmer to its absolute breaking point. From bumping it against asphalt over 5,000 times to completely submerging it in water, this machine went through it all. Here's how the STIHL FS 91 held up in some of the harshest tests imaginable.
The Bump Head Test: How Much Is Too Much?
First up was the bump head test, where the goal was to see just how many line feed "bumps" the head could endure before running out of trimmer string. Spoiler alert: it didn’t take long. After numerous bumps on hard concrete, the string was gone in no time—but the trimmer head stayed intact. Even with consistent abuse, the FS 91’s bump-feed mechanism kept doing its job.
Would you ever bump your trimmer this many times in a real-world scenario? Probably not. For a machine to hold up to this level of use is a testament to STIHL’s engineering.
Testing Against Asphalt and Concrete
Next, we decided to ramp things up. First, we trimmed along asphalt, then moved to concrete, pushing the FS 91 well beyond what a normal user would ever put it through. The edges of the bump head started melting under the heat and friction, but the trimmer remained operational. Even after repeated abuse, we were able to restring it and keep going.
At this point, the FS 91 was scorching hot—but it still showed no signs of slowing down. When the asphalt proved too soft for our liking, we moved to jagged concrete for an even tougher challenge. The FS 91 kept up, despite the flexing of its handle and the extreme friction.
Dragging and Dropping: Stress Testing the Shaft
To test the shaft's resilience, we dragged the FS 91 across hard surfaces and performed drop tests to simulate real-life accidents. Sure, the shaft got a slight curve and a noticeable "waffle," but you could still start the trimmer with ease. One pull, and it was good to go.
People often say STIHL trimmers might be sensitive to light impacts due to their valve train assembly. We decided to put that theory to the test with some serious drops and rough handling. The FS 91 didn’t miss a beat. Though it was worse for wear cosmetically, its performance remained unaffected.
Making It Hot and Wet: Submersion in Water
Because why stop at asphalt and concrete? We took the FS 91 to a retention pond and submerged it fully in water—with its air filter still on. Amazingly, it started up again after just one pull. Even though the motor had been running hot, the water didn’t stop it. At one point, the trimmer stopped briefly, but the quick restart proved its resilience.
The submersion test showed exactly how the FS 91 handles extreme conditions. Whether you're caught in the rain or trimming near damp areas, this machine is built to operate.
Dirt, Sand, and Neglect
If you've ever wondered how a trimmer handles when it's completely neglected, we answered that too. After removing the air filter, we introduced dirt directly into the airbox and even threw in some sand for good measure. While no machine likes this much abuse, the FS 91 kept running for a while longer, proving it could handle more than its fair share of poor maintenance.
For those curious about whether abuse like this mimics real use, the truth is: probably not. But it’s always good to know your tools can handle these extremes if needed.
Throwing It Across a Parking Lot
Because dragging wasn’t enough, we gave the FS 91 some air time. We launched it about 30 feet across a parking lot. Despite a bent handle and a cracked carburetor, it still tried to keep running. While the carburetor finally gave out after this level of extreme abuse, it’s safe to say you’d never encounter these stresses during routine lawn care.
Final Thoughts: Is the STIHL FS 91 Really That Durable?
The STIHL FS 91 proved itself as a reliable and durable string trimmer through every test, no matter how extreme. From asphalt and concrete abuse to submersion in water and dirt-filled air filters, this trimmer kept pushing through conditions that no homeowner or professional would normally encounter.
Of course, no tool is indestructible. At a certain point, even the most durable machines will fail under enough pressure. But what this test showed is that the STIHL FS 91 isn’t just tough—it’s built for the long haul. If you're looking for a string trimmer that can handle your toughest jobs (and then some), this might just be the one.
Got a product you want to see put to the test? Let us know! We’re always up for pushing the limits to see what’s really built to last.
Product Discussed In The Video
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